The Building Regulations 2000
Structure
APPROVED DOCUMENT
A1 Loading
A2 Ground movement
A3 Disproportionate collapse
2004 EDITION
MAIN CHANGES IN THE 2004
EDITION
This edition of Approved Document A,
Structure, replaces the 1992 Edition (with 1994
and 2000 amendments edition). The main
changes are:
Use of Guidance
a. Eurocodes: an announcement is given
regarding the forthcoming introduction of
the Structural Eurocodes and their
National Annexes.
b. House construction: reference is made
to the intended publication of guidance
by industry of alternative forms of house
construction to that of traditional
masonry.
A1 and A2
Traditional dwellings
c. The guidance on the sizing of timber
floors and roofs for traditional house
construction has been removed as the
Timber Tables are now published by
TRADA. However, the TRADA Tables are
referenced under Section 2B.
d. A revised map of basic wind speeds in
accordance with BS6399:Part 2 replaces
the superseded map which was based on
BS CP3 Chapter V.
e. Stainless steel cavity wall ties have been
specified to all houses regardless of their
location.
f. The guidance on masonry walls to
dwellings has been extended to enable
the rules to be applicable when using
either the appropriate British Standards
or the emerging BS EN CEN Standards.
g. The guidance on concrete foundations to
houses has been revised to align with the
recommendations given in the British
Standards and other authoritative
guidance. Recommendations on minimum
foundation depths have also been
included to counter the impact of
predicted climate changes.
h. The guidance on the design and
construction of domestic garages has
been extensively updated to reflect
modern practice.
A3
i. Disproportionate collapse: the
Application Limit to the Requirement (ie.
the 5 storey limit) has been removed so
as to bring all buildings under control of
the A3 Requirement.
The modified guidance has been
developed from commissioned research
and consideration of the
recommendations given in the
forthcoming Eurocode EN1991-
Accidental Actions.
Structure Approved Document A
PAGE
Use of Guidance 3
Loading and Ground Movement 5
The Requirements 5
Guidance 6
Introduction 6
Section 1: Codes, Standards and other
references for all building types 7
Loading 7
Structural work of timber 7
Structural work of masonry 7
Structural work of reinforced, pre-
or plain concrete 7
Structural work of steel 7
Structural work of aluminium 7
Foundations 7
Ground Movement (Requirement A2(b) 8
Existing buildings 8
Section 2: Sizes of structural elements
for certain residential buildings and
other small buildings of traditional
construction 9
General 9
Definitions 9
Section 2A: Basic requirements for
stability 10
Section 2B: Sizes of certain timber
members in floors and roofs for
dwellings. Areas at risk from House
Longhorn Beetle 11
Sizing of members 11
House Longhorn Beetle 11
Section 2C: Thickness of walls in
certain small buildings 12
Application 12
Wall types 12
The use of this section 12
Conditions relating to the building of
which the wall form part 12
PAGE
Thickness of walls 13
Conditions relating to the wall 16
Construction materials and workmanship 17
Loading on walls 24
End restraint 24
Openings, recesses, overhangs and
chases 26
Lateral support by roofs and floors 27
Interruption of lateral support 30
Small single storey non-
buildings and annexes 30
Section 2D: Proportions for masonry
chimneys above the roof surface 34
Height to width relationship 34
Section 2E: Foundations of plain
concrete 35
Conditions relating to the ground 35
Design provisions 35
Minimum width of strip foundations 35
Minimum depth of strip foundations 36
Section 3: Wall Cladding 37
General 37
Technical Approach 37
Loading 37
Fixings 37
Further Guidance 38
Section 4: Roof Covering 39
Materials 39
Recovering of roofs 39
DISPROPORTIONATE COLLAPSE 40
The Requirement 40
Guidance 41
Performance 41
Introduction 41
Section 5: Reducing the sensitivity
of the building to disproportionate
collapse in the event of an accident 42
Alternative Approach 43
Contents
1
A
Approved Document A
PAGE
DIAGRAMS
1. Size and proportion of residential
buildings of not more than 3 storeys 13
2. Size and proportion of non-
buildings and annexes 14
3. Determination of wall thickness 15
4. Parapet walls: height 16
5. Maximum floor area enclosed by
structural walls 17
6. Map showing wind speeds in m/s 18
7. Maximum height of buildings 19
8. Measuring storey and wall heights 20
9. Compressive strength of masonry
units 22
10. Declared compressive strength of
masonry units 23
11. Maximum span of floors 24
12. Differences in ground level 25
13. Openings in a buttressing wall 26
14. Buttressing 27
15. Sizes of openings and recesses 28
16. Lateral support by floors 29
17. Lateral support at roof level 30
18. Size and location of openings 31
19. Wall thickness 32
20. Horizontal and lateral restraint at
roof level 33
21. Proportions for masonry chimneys 34
22. Elevation of stepped foundation 35
23. Piers and chimneys 35
24. Foundation dimensions 35
25. Area at risk of collapse in the event
of an accident 44
PAGE
TABLES
1. Areas at risk from House Longhorn
Beetle 11
2. Wall types considered in this section 12
3. Minimum thickness of certain
external walls, compartment walls,
and separating walls 15
4. Imposed loads 17
5. Cavity wall ties 21
6. Compressive Strength of Masonry
Units complying with BS EN 771-
to 5 21
7. Normalised compressive strength
of masonry unit of clay and calcium
silicate blocks complying with BS
EN 771-
8. Value of factor ‘x’ 28
9. Lateral support for walls 28
10. Minimum width of strip foundations 36
11. Building Classes 42
Structure Approved Document A
2
A CONTENTS
THE APPROVED DOCUMENTS
This document is one of a series that has been
approved by the First Secretary of State for the
purpose of providing practical guidance with
respect to the requirements of Schedule 1 to
and Regulation 7 of the Building Regulations
2000 (SI 2000/2531) for England and Wales. SI
2000/2531 has been amended by the Building
(Amendment) Regulations 2001 (SI 2001/3335),
by the Building (Amendment) Regulations 2002
(SI 2002/440), by the Building (Amendment)
(No. 2) Regulations 2002 (SI 2002/2871), by the
Building (Amendment) Regulations 2003 (SI
2003/2692) and by the Building (Amendment)
Regulations 2004 (SI 2004/1465).
At the back of this document is a list of all
the documents that have been approved and
issued by the Secretary of State for this
purpose.
Approved Documents are intended to provide
guidance for some of the more common
building situations. However, there may well be
alternative ways of achieving compliance with
the requirements. Thus there is no obligation
to adopt any particular solution contained in
an Approved Document if you prefer to meet
the relevant requirement in some other way.
Other requirements
The guidance contained in an Approved
Document relates only to the particular
requirements of the Regulations which that
document addresses. The building work will
also have to comply with the requirements of
any other relevant paragraphs in Schedule 1 to
the Regulations.
There are Approved Documents which give
guidance on each of the parts of Schedule 1
and on regulation 7.
LIMITATION ON REQUIREMENTS
In accordance with regulation 8, the
requirements in Parts A to K and N of Schedule
1 to the Building Regulations do not require
anything to be done except for the purpose of
securing reasonable standards of health and
safety for persons in or about the buildings.
MATERIALS AND WORKMANSHIP
Any building work which is subject to
requirements imposed by Schedule 1 to the
Building Regulations should, in accordance
with regulation 7, be carried out with proper
materials and in a workmanlike manner.
You may show that you have complied with
regulation 7 in a number of ways. These
include the appropriate use of a product
bearing CE marking in accordance with the
Construction Products Directive (89/106/EEC)1
as amended by the CE Marking Directive
(93/68/EEC)2, or a product complying with an
appropriate technical specification (as defined
in those Directives), a British Standard, or an
alternative national technical specification of
any state which is a contracting party to the
European Economic Area which, in use, is
equivalent, or a product covered by a national
or European certificate issued by a European
Technical Approval Issuing body, and the
conditions of use are in accordance with the
terms of the certificate. You will find further
guidance in the Approved Document
supporting regulation 7 on materials and
workmanship.
Independent certification schemes
There are many UK product certification
schemes. Such schemes certify compliance
with the requirements of a recognised
document which is appropriate to the purpose
for which the material is to be used. Materials
which are not so certified may still conform to
a relevant standard.
Many certification bodies which approve such
schemes are accredited by UKAS.
Technical specifications
Building Regulations are made for specific
purposes; health and safety, energy
conservation and the welfare and convenience
of disabled people. Standards and technical
approvals are relevant guidance to the extent
that they relate to these considerations.
However, they may also address other aspects
of performance such as serviceability, or
aspects which although they relate to health
and safety are not covered by the Regulations.
When an Approved Document makes reference
to a named standard, the relevant version of
the standard is the one listed at the end of the
publication. However, if this version has been
revised or updated by the issuing standards
body, the new version may be used as a source
of guidance provided it continues to address
the relevant requirements of the Regulations.
The appropriate use of a product which
complies with a European Technical Approval
as defined in the Construction Products
Directive will meet the relevant requirements.
Use of Guidance
Approved Document A Structure
3
THE BUILDING REGULATIONS 2000 A
1 As implemented by the Construction Products
Regulations 1991 (S.1. 1991/1620).
2 As implemented by the Construction Products
(Amendment) Regulations 1994 (S. 1. 1994/3051).
The Department intends to issue periodic
amendments to its Approved Documents to
reflect emerging harmonised European
Standards. Where a national standard is to be
replaced by a European harmonised Standard,
there will be a co-
which either standard may be referred to. At
the end of the co-
standard will be withdrawn.
THE WORKPLACE (HEALTH,
SAFETY AND WELFARE)
REGULATIONS 1992
The Workplace (Health, Safety and Welfare)
Regulations 1992 contain some requirements
which affect building design. The main
requirements are now covered by the Building
Regulations, but for further information see:
Workplace health, safety and welfare, The
Workplace (Health, Safety and Welfare)
Regulations 1992, Approved Code of Practice
and Guidance; The Health and Safety
Commission, L24; Published by HMSO 1992;
ISBN 0-
The Workplace (Health, Safety and Welfare)
Regulations 1992 apply to the common parts of
flats and similar buildings if people such as
cleaners and caretakers are employed to work
in these common parts. Where the
requirements of the Building Regulations that
are covered by this Part do not apply to
dwellings, the provisions may still be required
in the situations described above in order to
satisfy the Workplace Regulations.
OTHER FORMS OF HOUSE
CONSTRUCTION
This Approved Document includes guidance on
structural elements of residential buildings of
traditional masonry construction. It is
recognised, however, that there are other
suitable forms of construction in use in the
housing sector some of which (e.g. timber
framed) have been in common use for a
number of years and have demonstrated an
adequate performance in compliance with the
A1 requirement. Such alternative forms include
prefabricated timber, light steel and pre-
concrete framed construction.
A number of guidance documents relating to
these alternative forms are presently being
developed by industry. The intention is to
reference these in this Approved Document as
soon as they become available and are
approved by the Secretary of State.
EUROCODES
The British Standards Institution will shortly be
publishing a series of Structural Eurocodes,
together with their National Annexes. These
Eurocodes are CEN Standards comprising
many Parts which, when used in conjunction
with their National Annexes and when approved
by the Secretary of State, are intended to be
referenced in this Approved Document as
practical guidance on meeting the Part A
Requirements.
Structure Approved Document A
4
A THE BUILDING REGULATIONS 2000
This Approved Document deals with the
following Requirements which are contained in
the Building Regulations 2000 (as amended by
SI 2001/3335, SI 2002/440, SI 2002/2871 and
SI 2003/2692.
The Requirements
Approved Document A Structure
5
LOADING AND GROUND MOVEMENT A1/2
Loading
A1. (1) The building shall be constructed so that the combined dead,
imposed and wind loads are sustained and transmitted by it to the
ground -
(a) safely; and
(b) without causing such deflection or deformation of any part
of the building, or such movement of the ground, as will
impair the stability of any part of another building.
(2) In assessing whether a building complies with sub paragraph (1)
regard shall be had to the imposed and wind loads to which it is likely
to be subjected in the ordinary course of its use for the purpose for
which it is intended.
Ground Movement
A2. The building shall be constructed so that ground movement
caused by :-
(a) swelling, shrinkage or freezing of the subsoil; or
(b) land-
shrinkage), in so far as the risk can be reasonably foreseen,
will not impair the stability of any part of the building.
Requirement Limits on application
Introduction
0.1 In the Secretary of State’s view the
requirements of A1 and A2 will be met by
following the recommendations given in the
documents listed in Section 1 or by adopting
the guidance in Sections 2-
a. Section 1 is relevant to all building types
and lists Codes, Standards and other
references for structural design and
construction but, where they do not give
precise guidance, consideration should be
given to paragraph 0.2.
b. Section 2 give sizes of structural
elements for certain residential buildings and
other small buildings of traditional
construction.
c. Section 3 gives guidance on the support
and fixing of wall cladding
d. Section 4 gives guidance where roofs are
to be re-
defined in the Regulations.
0.2 The safety of a structure depends on the
successful combination of design and
completed construction, particularly :
a. The design should be based on
identification of the hazards to which the
structure is likely to be subjected and
assessment of the risks. The selection of
relevant critical situations for design should be
made reflecting the conditions that can
reasonably be foreseen during future use.
b. Loading. Dead load, imposed load and
wind load should be in accordance with the
current Codes of Practice referred to in Section
1 of this document.
c. Properties of materials
d. Detailed design and assembly of the
structure
e. Safety factors
f. Workmanship
The numeric values of safety factors, whether
expressed explicitly or implicitly in design
equations, or design values, should be derived
from considerations of the above aspects of
design and construction as a whole. A change
in any one of these aspects may disturb the
safety of structure.
Loads used in calculations should allow for
possible dynamic, concentrated and peak load
effects that may occur.
0.3 Grandstands and structures erected in
places of public assembly may need to sustain
the synchronous or rhythmic movement of
numbers of people. It is important to ensure
that the design of the structure takes these
factors into account so as to avoid the
structure being impaired or causing alarm to
people using the structure.
Interim guidance on the design of grandstands
may be found in “Dynamic performance
requirements for permanent grandstands
subject to crowd action, Interim Guidance on
assessment and design” published by the
Institution of Structural Engineers, November
2001.
Supplementary advice on the dynamic testing
of grandstands and seating decking has been
published in an Advisory Note by the Institution
of Structural Engineers June 2002.
Guidance
Structure Approved Document A
6
A1/2 LOADING AND GROUND MOVEMENT
Introduction
1.1 This section is relevant to all building types
and lists codes, standards and other references
for structural design and construction.
References
1.2 Loading:
a. Dead and imposed loads
BS 6399 : Loading for buildings :
Part 1 : 1996 Code of practice for dead and
imposed loads.
b. Wind Loads
BS 6399 : Loading for buildings:
Part 2 : 1997 Code of practice for wind loads
BRE Digest 436 : Parts 1, 2 and 3 (Brief
guidance for using BS 6399 : Part 2).
c. Imposed roof loads
BS 6399 : Loading for buildings:
Part 3 : 1988 Code of practice for imposed roof
loads.
1.3 Structural work of timber:
BS 5268 : Structural use of timber :
Part 2 : 2002 Code of practice for permissible
stress design, materials and workmanship.
Part 3 : 1998 Code of practice for trussed
rafter roofs.
BS 8103 : Structural design of low-
buildings.
Part 3 : 1996 Code of practice for timber floors
and roofs for housing.
1.4 Structural work of masonry:
BS 5628 : Code of practice for use of masonry:
Part 1 : 1992 Structural use of unreinforced
masonry.
Part 2 : 2000 Structural use of reinforced and
prestressed masonry.
Part 3 : 2001 Materials and components,
design and workmanship.
BS 8103 : Structural design of low-
buildings:
Part 1 : 1995 Code of practice for stability, site
investigation, foundations and ground floor
slabs for housing.
Part 2 : 1996 Code of practice for masonry
walls for housing.
1.5 Structural work of reinforced, prestressed
or plain concrete:
BS 8110 : Structural use of concrete:
Part 1 : 1997 Code of practice for design and
construction.
Part 2 : 1985 Code of practice for special
circumstances.
Part 3 : 1995 Design charts for singly
reinforced beams, doubly reinforced beams and
rectangular columns.
BS 8103 : Structural design of low rise
buildings: Part 4 : 1995 Code of practice for
suspended concrete floors for housing.
1.6 Structural work of steel:
BS 5950 : Structural use of steelwork in
Building:
Part 1 : 2000 Code of practice for design in
simple and continuous construction : hot rolled
and welded sections.
Part 2 : 2001 Specification for materials,
fabrication and erection, hot rolled sections.
Part 3 : Design in composite construction :
Section 3.1 : 1990 Code of practice for design
of simple and continuous composite beams.
Part 4 : 1994 Code of practice for design of
composite slabs with profiled steel sheeting.
Part 5 : 1998 Code of practice for design of
cold formed thin gauge sections.
BRE Digest 437 -
mezzanine and raised storage.
1.7 Structural work of aluminium:
BS 8118 : Structural use of aluminium:
Part 1 : 1991 Code of practice for design.
Part 2 : 1991 Specification for materials,
workmanship and protection.
1.8 Foundations:
BS 8002 : 1994 Code of practice for earth
retaining structures.
BS 8004 : 1986 Code of practice for
foundations.
Section 1: Codes, Standards and
References for all Building types
Approved Document A Structure
7
CODES, STANDARDS AND REFERENCES A1/2
Ground Movement (Requirement
A2b.)
1.9 There may be known or recorded
conditions of ground instability, such as that
arising from landslides, disused mines or
unstable strata which, if ignored, can have a
devastating effect on the safety of a building
and its environs. Such conditions should be
taken into account in the design of the building
and its foundations. Attention is drawn to DOE
Planning Policy Guidance Note 14
Development on unstable land (obtainable from
the Stationary office), which sets out the broad
planning and technical issues relating to
development on unstable land.
The Department has also sponsored a series of
reviews aimed at determining the scale and
nature of problems arising from mining
instability, natural underground cavities and
adverse foundation conditions. Databases of
both subsidence incidents and subsidence
potential produced from these reviews are
available from the following licence holders :
British Geological Survey, Sir Kingsley Dunham
Centre, Keyworth, Nottingham NG12 5GG.
Landmark, 7 Abbey Court, Eagle Way, Exeter,
Devon EX2 7HY,
Peter Brett Associates, 16 Westcote Road,
Reading, Berkshire RG20 2DE.
Catalytic Data Ltd., The Spinney, 19 Woodlands
Road, Bickley, Kent BRI 2AD
The reports from these reviews, which include
1:250,000 scale maps showing the distribution
of the physical constraints, are available from
the following organisations :
Arup Geotechnics, 1991. Review of mining
instability in Great Britain.
Obtainable from Arup Geotechnics, Bede
House, All Saints, Newcastle-
2EB.
Applied Geology Ltd., 1994. Review of
instability due to natural underground cavities
in Great Britain.
Obtainable from Kennedy & Donkin Ltd., 14
Calthorpe Road, Edgbaston, Birmingham Bl5
1TH.
Wimpey Environmental Ltd., and National
House Building Council, 1995. Foundation
conditions in Great Britain, a guide for planners
and developers. Obtainable from ESNR
International Ltd., 16 Frogmore Road, Hemel
Hempstead, Hertfordshire HP3 9RW.
Existing buildings
1.10 Compliance with Part A (Structure) is
required in certain classes of change of use of
a building, subject to the control of Regulations
5 and 6. Guidance relevant to structural
appraisals related to ‘change of use’ is given in
the following documents :
a. BRE Digest 366 : Structural Appraisal of
Existing Buildings for Change of Use.
b. The Institution of Structural Engineers
Report Appraisal of Existing Structures, 1996.
Note: With reference to the item ‘design
checks’ in the above mentioned Institution of
Structural Engineers report the choice of
various partial factors should be made to suit
the individual circumstances of each case.
Structure Approved Document A
8
A1/2 CODES, STANDARDS AND REFERENCES
General
2.1 This Section is presented as follows:
Section 2A
Basic requirements for stability.
Section 2B
Sizes of certain timber members in floors and
roofs for dwellings.
Areas at risk from house longhorn beetle.
Section 2C
Thickness of masonry walls in certain
residential buildings of not more than 3 storeys,
small single storey non-
and annexes.
Section 2D
Proportions for masonry chimneys.
Section 2E
Foundations of plain concrete.
2.2 Section 2A gives general rules which must
be observed in following Sections 2B and 2C.
Sections 2B to 2E may be used independently
of each other.
Throughout this section the diagrams are only
illustrative and do not show all the details of
construction.
Definitions
2.3 The following meanings apply to terms
throughout this Section:
Buttressing wall A wall designed and
constructed to afford lateral support to another
wall perpendicular to it, support being provided
from the base to the top of the wall.
Cavity width The horizontal distance between
the two leaves of a cavity wall.
Compartment wall A wall constructed as a
compartment wall to meet the requirements of
regulation B3(2).
Dead load The load due to the weight of all
walls, permanent partitions, floors, roofs and
finishes including services, and all other
permanent construction.
Imposed load The load assumed to be
produced by the intended occupancy or use,
including the weight of movable partitions,
distributed, concentrated, impact, inertia and
snow loads, but excluding wind loads.
Pier A member which forms an integral part of
a wall, in the form of a thickened section at
intervals along the wall, so as to afford lateral
support to the wall to which it is bonded or
securely tied.
Separating wall A wall or part of a wall which
is common to adjoining buildings, and
constructed to meet the requirements of
regulation B3(2).
Spacing The distance between the longitudinal
centres of any two adjacent timber members of
the same type, measured in the plane of floor,
ceiling or roof structure.
Span The distance measured along the centre
line of a member between the centres of any
two adjacent bearings or supports.
Supported Wall A wall to which lateral support
is afforded by a combination of buttressing
walls piers or chimneys acting in conjunction
with floor(s) or roof.
Wind load The load due to the effect of wind
pressure or suction.
Section 2: Sizes of Structural Elements for
certain residential buildings and other small
buildings of Traditional Construction
Approved Document A Structure
9
SIZES OF STRUCTURAL ELEMENTS A1/2
2A1 This section must be used in conjunction
with sections 2B and 2C and its principles
relate to all forms of low rise residential
buildings.
2A2 Adequate provision shall be made to
ensure that the building is stable under the
likely imposed and wind loading conditions.
This will commonly necessitate meeting the
following requirements:
a. That the overall size and proportioning of
the building are limited in accordance with the
specific guidance for each form of
construction.
b. That a suitable layout of walls (both
internal and external) forming a robust 3
dimensional box structure in plan is
constructed with restriction on the maximum
size of cells measured in accordance with the
specific guidance for each form of
construction.
c. That the internal and external walls are
adequately connected by either masonry
bonding or by using mechanical connections.
d. That the intermediate floors and roof are
of such construction and interconnection with
the walls that they provide local support to the
walls and also act as horizontal diaphragms
capable of transferring the wind forces to
buttressing elements of the building.
Note: A traditional cut timber roof (i.e. using
rafters, purlins and ceiling joists) generally has
sufficient built in resistance to instability and
wind forces (eg from either hipped ends, tiling
battens, rigid sarking, or the like). However, the
need for diagonal rafter bracing equivalent to
that recommended in BS 5268: Part 3: 1998 or
Annex H of BS 8103: Part 3: 1996 for trussed
rafter roofs, should be considered especially
for single-
greater than 40° pitch to detached houses.
Section 2A: Basic Requirements for Stability
Structure Approved Document A
10
A1/2 SIZES OF STRUCTURAL ELEMENTS
Sizing of Members
2B1 Guidance on the sizing of certain
members in floors and roofs is given in “Span
tables for solid timber members in floors,
ceilings and roofs (excluding trussed rafter
roofs) for dwellings”, published by TRADA,
available from Chiltern House, Stocking Lane,
Hughenden Valley, High Wycombe, HP14 4ND,
Bucks.
Alternative guidance is available in BS 5268:
Part 2: 2002 Code of Practice for permissible
stress design, materials and workmanship, BS
5268: Part 3: 1998, Code of Practice for
trussed rafter roofs and BS 8103: Part 3:
Structural design of low-
Practice for timber floors and roofs for
dwellings.
House Longhorn Beetle
2B2 In the geographical areas specified in
Table 1, softwood timber for roof construction
or fixed in the roof space, including ceiling
joists within the void spaces of the roof, should
be adequately treated to prevent infestation by
the House Longhorn Beetle (Hylotrupes bajulus
L).
Guidance on suitable preservative treatments is
given within the British Wood Preserving and
Damp-
revision), available from 1 Gleneagles House,
Vernongate, South Street, Derby DE1 1UP.
Section 2B: Sizes of certain timber
members in floors and roofs for dwellings.
Areas at risk from House Longhorn Beetle
Approved Document A Structure
11
SIZES OF STRUCTURAL ELEMENTS A1/2
Geographical Area
In the Borough of Bracknell Forest the parishes of Sandhurst and Crowthorne.
The Borough of Elmbridge
In the District of Hart, the parishes of Hawley and Yateley
The District of Runnymede
The Borough of Spelthorne
The Borough of Surrey Heath
In the Borough of Rushmoor, the area of the former district of Farnborough The Borough of Woking
Table 1 Areas at risk from House Longhorn Beetle
Application
2C1 This Section applies to the following
building types:
a. residential buildings of not more than
three storeys, and
b. small single storey non-
buildings, and
c. small buildings forming annexes to
residential buildings. (including garages and
outbuildings).
Wall types
2C2 Only the types of wall given in Table 2,
which must extend to the full storey height, and
parapet walls are considered in this section.
The use of this Section
2C3 When using this Section it should be
noted that:
a. this section must be used in conjunction
with Section 2A;
b. if wall thickness is to be determined
according to paragraphs 2C5 to 2C13, all
appropriate design conditions given in this
section must be satisfied;
c. walls should comply with the relevant
requirements of BS 5628: Part 3:2001, except
as regards the conditions given in paragraphs
2C4 and 2C14 to 2C38.
d. in formulating the guidance of this
section the worst combination of
circumstances likely to arise was taken into
account. If a requirement of this part is
considered too onerous in a particular case it
may be appropriate to consider a minor
departure on the basis of judgement and
experience, or to show adequacy by
calculation in respect of the aspect of the wall
which is subject to the departure rather than
for the entire wall;
e. the guidance given is based upon the
compressive strengths of bricks and blocks
being not less than indicated in Tables 6 and 7.
BS 5628 Part 1: 1992 gives design strengths
for walls where the suitability for use of
masonry units of other compressive strengths
is being considered.
Conditions relating to the
building of which the wall
forms part
2C4 This Section applies only to buildings
having proportions within the following
parameters (see Diagrams 1 and 2)
a. residential buildings of not more than 3
storeys:
i. the maximum height of the building
measured from the lowest finished
ground level adjoining the building to the
highest point of any wall or roof should
not be greater than 15m, subject to the
limits of paragraph 2C16,
ii. the height of the building H should not
exceed twice the least width of the
building W1,
iii. the height of the wing H2 should not
exceed twice the least width of the wing
W2 where the projection P exceeds twice
the width W2.
b. small single-
buildings: height H should not exceed 3m and
W (being the greatest length or width of the
building) should not exceed 9m (see Diagram
2), subject to the limits of paragraph 2C16.
Section 2C: Thickness of walls in certain
small buildings
Structure Approved Document A
12
A1/2 SIZES OF STRUCTURAL ELEMENTS
Residential buildings of up to three storeys
external walls
internal load bearing walls
compartment walls
separating walls
Small single storey non-
external walls
internal load bearing walls
Table 2 Wall types considered in this Section
c. annexes: height H as variously indicated
in Diagram 2 should not exceed 3m, subject to
the limits of paragraph 2C16.
Thickness of walls
2C5 General wall thickness may be determined
according to this Section provided:
a. condition relating to the building of which
the wall forms part (see paragraphs 2C4, 2C14
to 2C16, 2C38) and
b. condition relating to the wall (see
paragraphs 2C17 to 2C37) are met. (See
diagram 3)
2C6 Solid external walls, compartment walls
and separating walls in coursed brickwork
or blockwork: Solid walls constructed of
coursed brickwork or blockwork should be at
least as thick as 1/16 of the storey height.
Further requirements are given in Table 3.
2C7 Solid external walls, compartment walls
and separating walls in uncoursed stone,
flints etc.: The thickness of walls constructed
in uncoursed stone, flints, clunches, of bricks
or other burnt or vitrified material should not be
less than 1.33 times the thickness determine
by paragraph 2C6.
2C8 Cavity walls in coursed brickwork or
blockwork: All cavity walls should have leaves
at least 90mm thick and cavities at least 50mm
wide. The wall ties should have a horizontal
spacing of 900mm and a vertical spacing of
450mm, which is equivalent to 2.5 ties per
square metre. Wall ties should also be
provided, spaced not more than 300mm apart
vertically, within a distance of 225mm from the
vertical edges of all openings, movement joints
and roof verges. For selection of wall ties for
use in a range of cavity widths refer to Table 5.
For specification of cavity wall ties refer to
paragraph 2C19.
For external walls, compartment walls and
separating walls in cavity construction, the
combined thickness of the two leaves plus
10mm should not be less than the thickness
determined by paragraph 2C6 and Table 3 for a
solid wall of the same height and length.
2C9 Walls providing vertical support to
other walls: Irrespective of the material used in
the construction, a wall should not be less in
thickness than any part of the wall to which it
gives vertical support.
2C10 Internal loadbearing walls in
brickwork or blockwork: (except compartment
walls or separating walls) should have a
thickness not less than:
(specified thickness from Table 3)
-
2
Approved Document A Structure
13
SIZES OF STRUCTURAL ELEMENTS A1/2
if P is more than 2W2
then W2 to be not less than 0.5 H2
See para 2C4
W1 to be not less than 0.5 H
Maximum height Minimum height
H
not to
exceed
15m
lowest
ground level
W1 W1
W1 W2
H2
H H
P
Diagram 1 Size and proportion of residential buildings of not more than 3 storeys
Continued on page 16
Structure Approved Document A
14
A1/2 SIZES OF STRUCTURAL ELEMENTS
II
II
II
II
II
II
a. Non-
b. Annexes
See para 2C4b and 2C4c
Flat roof buildings
Flat roof annexes
annexe
PItched roof annexes
(type 1)
PItched roof annexes
(type 2)
annexe
annexe
Pitched roof buildings
Maximum roof
slope 40˚
Maximum roof
slope 40˚
Residential
building
Residential
building
H
3.0 m
max.
H
3.0 m
max.
H
H
H
H
3.5 m
max.
3.0 m
max.
4.5 m
max.
3.0 m
max.
H
3.6 m
max.
Note
Height H should be measured
from top of the foundation or
from the underside of the floor
slab where this provides effective
lateral restraint.
3.5 m
max.
3.5 m
max.
3.0 m
max.
Maximum roof
slope 40˚
Diagram 2 Size and proportion of non-
Approved Document A Structure
15
SIZES OF STRUCTURAL ELEMENTS A1/2
YES
YES
NO
NO
See para 2C5
Conditions – building
(a) limitations on size and proportion of building and
parts of the building (paragraph 2C4 and 2C38)
(b) maximum allowable floor areas (paragraph 2C14)
(c) maximum imposed and wind loads
(paragraphs 2C15 and 2C16)
Conditions – wall
(a) maximum allowable length and height of wall
(paragraphs 2C17–2C18)
(b) construction materials and workmanship
(paragraphs 2C19–2C22)
(c) loading on walls (paragraph 2C23–2C24)
(d) end restraints (paragraphs 2C25–2C27)
(e) openings, recesses, overhangs and chases
(paragraphs 2C28–2C31)
(f) lateral support by roofs and floors
(paragraphs 2C32–2C37)
(g) conditions relating to external walls of small
single storey non-
annexes (paragraphs 2C38)
Conditions relating
to the building of
which the wall
forms part
Conditions relating
to the wall
Are
condtions
relating to
the wall
satisfied?
Wall thickness
given in paragraphs
2C6 to 2C13
may be used
Outside scope
of this part
Outside scope
of this part
Are
condtions
relating to
the building
satisfied?
Diagram 3 Determination of wall thickness
Height of wall Length of wall Minimum thickness of wall
not exceeding 3.5m not exceeding 12m 190mm for whole of its height
exceeding 3.5m but not exceeding 9m not exceeding 9m 190mm for whole of its height
exceeding 9m 290mm from the based for the height of
one storey and 190mm for the rest of its height
exceeding 9m but not exceeding 12m not exceeding 9m 290mm from the based for the height of
one storey and 190mm for the rest of its height
exceeding 9m 290mm from the base for the height of
but not exceeding 12m two storeys and 190mm for the rest of its height
Table 3 Minimum thickness of certain external walls, compartment walls and
separating walls
except for a wall in the lowest storey of a three
storey building, carrying load from both upper
storeys, which should have a thickness as
determined by the equation or 140mm
whichever is the greatest.
2C11 Parapet walls: The minimum thickness
and maximum height of parapet walls should
be as given in Diagram 4.
2C12 Single leaves of certain external walls:
The single leaf of external walls of small single
storey non-
need be only 90mm thick, notwithstanding
paragraphs 2C38
2C13 Modular bricks and blocks: Where walls
are constructed of bricks or blocks having
modular dimensions derived from BS6649 -
1985, wall thicknesses prescribed in this
section which derive from a dimension of brick
or block may be reduced by an amount not
exceeding the deviation from work size
permitted by a British Standard relating to
equivalent sized bricks or blocks made of the
same material.
2C14 Maximum floor area: The guidance of
this Section assumes that no floor enclosed by
structural walls on all sides exceeds 70m2; and
that no floor without a structural wall on one
side exceeds 36m2. (See Diagram 5)
2C15 Imposed loads on roofs, floors and
ceilings: The design considerations given in
this Section are intended to be adequate for
the imposed loads given in Table 4.
2C16 Maximum height of buildings: The design
guidance in this section is based on BS 6399 :
Part 2 : 1997. The maximum heights of
buildings given in Table c of Diagram 7
correlate to various site exposure conditions
and wind speeds. A map showing wind speeds
is given in Figure 1 of Diagram 6.
Conditions relating to the wall
2C17 Maximum allowable length and height
of the wall: This Section does not deal with
walls longer than 12m, measured from centre
to centre of buttressing walls, piers or
chimneys providing restraint, or with walls
exceeding 12m in height. (see also Table 3).
Structure Approved Document A
16
A1/2 SIZES OF STRUCTURAL ELEMENTS
level of junction
of wall and
structural roof
Type A
Cavity
wall
Note: t should be less than or equal to T
See para 2C11
Hp
t1
t
T
t2
level of junction
of wall and
structural roof
Type B
Cavity
wall
Hp
t
T
Wall
type
Thickness
(mm)
Parapet height Hp
to be not more than
(mm)
t1 +t2
equal or less than 200 600
t = 150 600
t1 +t2
greater than 200
equal or less than 250 860
t = 190 760
t = 215 860
Diagram 4 Parapet walls: height
2C18 Rules of measurement for heights of
walls and storeys: The height of a wall or a
storey should be measured in accordance with
the rules in Diagram 8.
Construction materials and
workmanship
2C19 Wall ties: Wall ties should either comply
with BS 1243, DD 140, or BS EN 845-
should be material references 1 or 3 in BS EN
845 Table A 1 austenitic stainless steel. Wall
ties should be selected in accordance with
Table 5 of this A. D.
2C20 Masonry Units: Walls should be properly
bonded and solidly put together with mortar and
constructed of masonry units conforming to:-
a. clay bricks or blocks conforming to BS
3921: 1985 or BS 6649: 1985 or BS EN 771-
b. calcium silicate bricks conforming to BS
187: 1978 or BS 6649: 1985 or BS EN 771-
c. concrete bricks or blocks conforming to
BS 6073: Part 1: 1981 or BS EN 771-
d square dressed natural stone conforming
to the appropriate requirements described in
BS EN 771-
e. Manufactured stone complying with BS
6457: 1984 and BS EN 771-
2C21 Compressive strength of masonry
units: Minimum compressive strength
requirements for masonry units according to
BS Standards and BS EN Standards are given
in Diagrams 9 and 10 respectively.
With reference to Diagram 9, the compressive
strengths given for bricks and blocks are those
values in accordance with the appropriate
British Standards ie. BS 3921, BS 6073-
187, BS 5390 and BS 6649.
With reference to Diagram 10, the masonry
units indicated for Conditions A, B and C
should have declared compressive strengths of
not less than the values given in Table 6.
Normalised compressive strengths for block
sized clay and calcium silicate masonry units
not complying with brick dimensional format
are given in Table 7.
Approved Document A Structure
17
SIZES OF STRUCTURAL ELEMENTS A1/2
Area not
exceeding 70m2.
Area not
exceeding 70m2.
Area not
exceeding 70m2.
Area not
exceeding
36m2.
Area not
exceeding
36m2.
Area not
exceeding
36m2.
Area not
exceeding
36m2.
a. Structural walls on all sides b. Structural walls on three sides
See para 2C14
Diagram 5 Maximum floor area enclosed by structural walls
Element Loading
distributed loads
roof 1.00 kN/m2 for spans not exceeding 12m
1.5 kN/m2 for spans not exceeding 6m
floors distrubted load: 2.00kN/m2
ceilings distributed load: 0.25kN/m2
together with concentrated load: 0.9kN
Table 4 Imposed Loads
Continued on page 24
Structure Approved Document A
18
A1/2 SIZES OF STRUCTURAL ELEMENTS
Figure 2 Topographic zones for Factor T
See para 2C16
zone 2
0.25Lu
zone 1
0.25Lu 0.4Lu
zone 2
0.4Lu
zone 3
1.2Lu
Lu
Cliffs and
Escarpments
Wind direction
zone 2
0.4Lu
zone 1
0.4Lu 0.4Ld
zone 2
0.4Ld
Lu Ld
Wind direction
Hills and Ridges
Lu – is slope on upwind side
Ld – is slope on downwind side
Figure 1 Map of wind speeds in m/s
24
24
25
25
23
23
24
23
22
20
21
24
Newcastle
Carlisle
Preston Leeds
York
Liverpool Manchester
Sheffield
Stoke
Nottingham
Leicester
Birmingham
Aberystwyth Northampton
Bedford
Norwich
Kingstonupon-
Hull
Ipswich
Oxford
LONDON
Bournemouth Brighton
Bristol
Cardiff
Plymouth
Swansea
Diagram 6 Map showing wind speeds in m/s for maximum height of buildings
Approved Document A Structure
19
SIZES OF STRUCTURAL ELEMENTS A1/2
Diagram 7 Maximum height of buildings
See para 2C16
Road map
wind spread V
from Figure 1
diagram 6
Find the topographic
zone for the
site from Figure 2
diagram 6 and obtain
factor from Table a
Obtain value of
factor A
from Table b
Calculate
value of factor S
from:
S = V x T x A
Obtain maximum
allowable building
height from
Table c
Table b Factor A
Topographic category and average slope of whole Factor T
hillside, ridge, cliff or escarpment Zone 1 Zone 2 Zone 3
Category 1 : Nominally flat terrain, average slope < 1/20 1.0 1.0 1.0
Category 2 : Moderately steep terrain, average slope < 1/5 1.24 1.13 1.10
Category 3 : Steep terrain, average slope > 1/5 1.36 1.20 1.15
Table b Factor A
Site Altitude (m) Factor A
0 1.00
50 1.05
100 1.10
150 1.15
200 1.20
300 1.30
400 1.40
Table c Maximum allowable building height (m)
Factor Country Sites Town Sites*
S Distance to the coast Distance to the coast
< 10km 10–50km > 50km < 10km 10–50km > 50km
24 15 15 15 15 15 15
25 11.5 14.5 15 15 15 15
26 8 10.5 13 15 15 15
27 6 8.5 10 15 15 15
28 4.5 6.5 8 13.5 15 15
29 3.5 5 6 11 13 14.5
30 3 4 5 9 11 12.5
31 3.5 4 8 9.5 10.5
32 3 3.5 7 8.5 9.5
33 3 6 7.5 8.5
34 5 7 8
35 4 6 7
36 3 5.5 6
37 4.5 5.5
38 4 5
39 3 4
40 3
Note: Outside these zones factor T = 10
* For sites on the outskirts of towns not sheltered by other buildings use the values for Country sites
Structure Approved Document A
20
A1/2 SIZES OF STRUCTURAL ELEMENTS
See para 2C18
Top of foundation
Ground level
2.7m max.
H1 H2 H3
Hp II
II
II
D
C
B
A
Base of wall
(see note)
A1
B1
II
2.7m max.
2.7m max.
Line of base
of gable.
2.7m max.
Line of lateral
support to gable
wall along roof
slope.
Line of top
of gable.
Top of wall
or base of
parapet
Line of lateral
support to gable
at ceiling level.
Underside of
roof joist
Key
(a) Measuring Storey Heights
A1 is the ground storey height if the ground floor provides
effective lateral support to the wall i.e. is adequately tied to
the wall or is a suspended floor bearing on the wall.
A is the ground storey height if the ground floor does not
provide effective lateral support to the wall.
Note: If the wall is supported adequately and permanently
on both sides by suitable compact material, the base of the
wall for the purposes of the storey height may be taken as
the lower level of this support. (Not greater than 3.7m
ground storey height.)
B is the intermediate storey height.
B1 is the top storey height for wall which do not include a
gable.
C is the top storey height where lateral support is given to
the gable at both ceiling level and along the roof slope.
D is the topstorey height for the external walls which include
a gable where lateral support is given to the gable only
along the roof slope.
(b) Measuring Wall Heights
H1 is the height of an external wall that does not include a
gable.
H2 is the height of an internal or separating wall which is
built up to the underside of the roof.
H3 is the height of an external wall which includes a gable.
Hp is the height of a parapet (see Diagram 4). If Hp is
more than 1.2m add to Hp to H1.
Diagram 8 Measuring storey and wall heights
Approved Document A Structure
21
SIZES OF STRUCTURAL ELEMENTS A1/2
Normal cavity
Permissible type of tie
width mm Tie length mm Tie Shape in accordance BS EN 845-
(Note 1) (Note 2) with BS 1243* (Note 4)
50 to 75 200 Butterfly, double triangle or vertical twist Types 1, 2, 3 or 4 to DD
140-
76 to 90 225 Double triangle or vertical twist
selected on the basis of the design
91 to 100 225 Double triangle (Note 3) or vertical twist
loading and design cavity width.
101 to 125 250 Vertical twist
126 to 150 275 Vertical twist *Although BS1243 and DD 140-
151 to 175 300 Vertical twist withdrawn on 1 February 2005, the tie user classes
(types) given in Tables 1 and 3 of the latter
176 to 300 (See Note 2) Vertical twist style document can continue to be used after this date.
Notes
1 Where face insulated blocks are used the cavity width should be measured from the face of the masonry unit.
2 The embedment depth of the tie should not be less than 50mm in both leaves. For cavities wider than 180mm calculate the
length as the structural cavity width plus 125mm and select the nearest stock length.
3 Double triangle ties of this shape having a strength to satisfy Type 2 of DD 140-
should be consulted if 225mm long double triangle format ties are needed for 91 to 100mm cavities.
4 Where BS EN 845-
2, 3 or 4) relevant to the performance levels given in DD140-
Table 5 Cavity wall ties
Masonry Clay masonry units to Calcium Silicate masonry Aggregate Autoclaved Manufactured
Unit BS EN 771-
Masonry Masonry Masonry
Units to units to units to
BS EN 771-
Condition A (See diagram 10)
Brick Group 1 Group 2 Group 1 Group 2 6.0 –
6.0 9.0 6.0 9.0
Block See Table 7 See Table 7 See Table 7 See Table 7 3.1* 3.1
Condition B (See diagram 10)
Brick Group 1 Group 2 Group 1 Group 2 9.0 –
9.0 13.0 9.0 13.0
Block See Table 7 See Table 7 See Table 7 See Table 7 7.7* 7.7
Condition C (See diagram 10)
Brick Group 1 Group 2 Group 1 Group 2 18.0 –
18.0 25.0 18.0 25.0
Block See Table 7 See Table 7 See Table 7 See Table 7 7.7* 7.7
*These values are dry ground strengths to BS EN 772-
Notes
1. This table applies to Group 1 and Group 2 units.
2. For the EN 771 series of standards for masonry units the values of declared compressive strengths (N/mm2) given in Table 6 are
mean values.
3. Brick: a masonry unit having work sizes not exceeding 337.5 mm in length or 112.5 mm in height.
4. Block: a masonry unit exceeding either of the limiting work sizes of a brick and with a minimum bed height of 190mm. For blocks
with smaller bed heights, excluding cuts or make up units, the strength requirements are as for brick except for solid external
walls where the blocks should have a compressive strength at least equal to that shown for block for an inner leaf of a cavity wall
in the same position.
5. Group 1 masonry units have not more than 25% formed voids (20% for frogged bricks). Group 2 masonry units have formed
voids greater than 25%, but not more than 55%.
Table 6 Declared Compressive Strength of Masonry Units complying with
BS EN 771 -
Any unit complying with BS EN 771-
be acceptable for conditions A, B and C
Structure Approved Document A
22
A1/2 SIZES OF STRUCTURAL ELEMENTS
Hs
Hs
Hs
Hs
Hf
Hs
a. One Storey
b. Two Storeys c. Three Storeys
Underside
of
structural
roof
Underside
of
structural
roof
Underside
of
structural
roof
Topside of
structural floor
Topside of
structural floor
This wall to be at
least 140mm thick
in blockwork or
215mm thick in
brickwork below ground
floor level if height
Hf exceeds 1m.
See para 2C21
Key
Brick 5N/mm2
Block 2.8N/mm2
Brick 15N/mm2
Block 7N/mm2
Where
Hf Less than or equal to 1m – Brick 5N/mm2
Hf Less than or equal to 1m – Block 2.8N/mm2
Where
Hf Greater than 1m – Brick 7N/mm2
Hf Greater than 1m – Block 7N/mm2
Brick 7N/mm2
Block 7N/mm2
Cavity
wall
Internal
wall
Underside
of
structural
roof
Underside
of
structural
roof
Underside
of
structural
roof
Topside of
structural floor
Cavity
wall
Internal
wall
This wall to
be at least
140mm thick
blockwork or
215mm thick
brickwork.
Hs
Diagram 9 Compressive strength of masonry units
Notes
1 If Hs is not greater than 2.7m, the
compressive strength of bricks or blocks
should be used in walls as indicated by the
key.
2 If Hs is greater than 2.7m, the
compressive strength of bricks or blocks
used in the wall shall either be at least
7N/sq mm or as indicated by the key,
whichever is the greater.
3 If the external wall is solid
construction the masonry units should have
a compressive strength of at least that
shown for the internal leaf of a cavity wall in
the same position.
4 The guidance given in the diagram for
walls of two and three storey buildings
should only be used to determine the
compressive strength of the masonry units
where the roof construction is of timber.
Approved Document A Structure
23
SIZES OF STRUCTURAL ELEMENTS A1/2
Hs
Hs
Hs
Hs
Hf
Hs
a. One Storey
b. Two Storeys c. Three Storeys
Underside
of
structural
roof
Underside
of
structural
roof
Underside
of
structural
roof
Topside of
structural floor
Topside of
structural floor
This wall to be at
least 140mm thick
in blockwork or
215mm thick in
brickwork below ground
floor level if height
Hf exceeds 1m.
See para 2C21
Key
Condition A
Condition C
Where
Hf Less than or equal to 1m, Condition A
Where
Hf Greater than 1m, Condition B
Condition B
Cavity
wall
Internal
wall
Underside
of
structural
roof
Underside
of
structural
roof
Underside
of
structural
roof
Topside of
structural floor
Cavity
wall
Internal
wall
This wall to
be at least
140mm thick
blockwork or
215mm thick
brickwork.
Hs
Diagram 10 Declared compressive strength of masonry units
Notes
1 If Hs is not greater than 2.7m, the
compressive strength of bricks or blocks
should be used in walls as indicated by the
key.
2 If Hs is greater than 2.7m, the
compressive strength of bricks or blocks
used in the wall should be at least Condition
B, or as indicated by the key, whichever is
the greater.
3 If the external wall is solid
construction, the masonry units should have
a compressive strength of at least that
shown for the internal leaf of a cavity wall in
the same position.
4 The guidance given in the diagram for
walls of two and three storey buildings
should only be used to determine the
compressive strength of the masonry units
where the roof construction is of timber.
2C22 Mortar: Mortar should be:
a.
i. Mortar designation (iii) according to BS
5628:Part 3:2001
ii. Strength class M4 according to BS EN
998 -
iii 1:1: 5 or 6 CEM 1, lime and fine
aggregate measured by volume of dry
materials, or
b. of equivalent or greater strength and
durability to the specification in a. above.
Loading on walls
2C23 Maximum span of floors: The maximum
span for any floor supported by a wall is 6m
where the span is measured centre to centre of
bearing. (see Diagram 11)
2C24 Other loading conditions:
a. Vertical loading on walls should be
distributed. This may be assumed for concrete
floor slabs, precast concrete floors, and timber
floors designed in accordance with Section 2B,
and where the bearing length for lintels is
150mm or greater. Where a lintel has a clear
span of 1200mm or less the bearing length may
be reduced to 100mm.
b. differences in level of ground or other
solid construction between one side of the wall
and the other should be less than 4 times the
thickness of the wall as shown in Diagram 12.
c. the combined dead and imposed load
should not exceed 70kN/m at base of wall. (see
Diagram 12)
d. walls should not be subjected to lateral
load other than from wind, and that covered by
paragraph 2C24(b).
End restraint
2C25 Vertical Lateral Restraint to Walls
The ends of every wall should be bonded or
otherwise securely tied throughout their full
height to a buttressing wall, pier or chimney.
Long walls may be provided with intermediate
buttressing walls, piers or chimneys dividing
the wall into distinct lengths within each storey;
each distinct length is a supported wall for the
purposes of this section. The intermediate
buttressing walls, piers or chimneys should
provide lateral restraint to the full height of the
supported wall, but they may be staggered at
each storey.
2C26 Buttressing Walls
If the buttressing wall is not itself a supported
wall its thickness T2 should not be less than :
Structure Approved Document A
24
A1/2 SIZES OF STRUCTURAL ELEMENTS
Standard Condition (See diagram 10) Group 1 masonry units Group 2 masonry units
Clay masonry units to A 5.0 8.0
BS EN 771-
masonry units to BS EN 771-
C 15.0 21.0
Notes:
1 Values in this Table are normalised compressive strengths (N/mm2). Compressive strengths of masonry units should be derived
according to EN 772-
2 The Table applies to clay and calcium silicate block masonry units where the work size exceeds 337.5mm in length or 112.5mm in
height.
3 Group 1 masonry units have not more than 25% formed voids (20% for frogged bricks). Group 2 masonry units have formed voids
greater than 25%, but not more than 55%.
Table 7 Normalised compressive strength of masonry units of clay and calcium
silicate blocks complying with BS EN 771-
See para 2C23
a. Floor member
bearing on wall
centre line
of bearing
centre line
of bearing
b. Floor member
bearing on
joist hanger
floor span
floor
maximum 6m
floor span
maximum 6m
wall
floor
Diagram 11 Maximum span of floors
Continued on page 26
Approved Document A Structure
25
SIZES OF STRUCTURAL ELEMENTS A1/2
Retained
height
H
H should be less
than or equal to 1m
and less than or
equal to 4t
W
i)
t
Retained
height
H
H should be less
than or equal to 1m
and less than or
equal to 4t
Combined dead and
imposed load W should
not exceed 70kN/m at
base of wall.
W
iii)
t
Concrete fill
to wall cavity
Retained
height
H
H should be less
than or equal to 1m
and less than or
equal to 4(t1 + t2)
W
ii)
t1
t2
Clear wall cavity
(unfilled)
b. Maximum differences in permitted level
a. Situations where differences in level may occur
See para 2C24b
Combined dead and
imposed load W should
not exceed 70kN/m at
base of wall.
Ground
supported
floor slab
Retained
height
Suspended
ground floor
Void
To be level for
a distance of not
less than 1.25H
W
W W
H
i)
Suspended
ground floor
Retained
height
Retained
height
For value of H
see (b.) below
W
Void
ii)
iii)
Diagram 12 Differences in ground levels
Notes
1 Floor slabs in figure b have been
omitted for clarity and may be on either side
of the walls shown.
2 Cavity walls should be tied in
accordance with Table 5.
3 These recommendations apply only to
circumstances where there is a full storey
height of masonry above the upper retained
level.
a. half the thickness required by this section
for an external or separating wall of similar
height and length less 5mm, or
b. 75mm if the wall forms part of a dwelling
house and does not exceed 6m in total height
and 10m in length, and
c. 90mm in other cases.
The length of the buttressing wall should be at
least 1/6 of the overall height of the supported
wall and be bonded or securely tied to the
supporting wall and at the other end to a
buttressing wall, pier or chimney.
The size of any opening in the buttressing wall
should be restricted as shown in Diagram 13.
2C27 Design criteria for piers and chimneys
providing restraint:
a. piers should measure at least 3 times the
thickness of the supported wall and chimneys
twice the thickness, measured at right angles
to the wall. Piers should have a minimum width
of 190mm (see Diagram 14)
b. the sectional area on plan of chimneys
(excluding openings for fireplaces and flues)
should be not less than the area required for a
pier in the same wall, and the overall thickness
should not be less than twice the required
thickness of the supported wall. (see Diagram
14)
Openings, recesses, overhangs
and chases
2C28 General:
The number, size and position of openings and
recesses should not impair the stability of a
wall or the lateral restraint afforded by a
buttressing wall to a supported wall.
Construction over openings and recesses
should be adequately supported.
Structure Approved Document A
26
A1/2 SIZES OF STRUCTURAL ELEMENTS
the length of the
buttressing wall should be
at least 1/6 of the overall
height of the supported
wall
See para 2C26
an opening or recess greater
than 0.1m2 shall be at least
550mm from the supported wall
The opening height should not be more than
0.9 times the floor to ceiling height and the
depth of the lintel including any masonry
over the opening should be not less than 150mm.
buttressing
wall
there may be
one opening or
recess not more
than 0.1m2 at
any position height of
supported
wall
550mm
T2
Diagram 13 Openings in a buttressing wall
Notes
1 The buttressing wall should be bonded
or securely tied to the supported wall and at
the other end to a buttressing wall, pier or
chimney.
2 Openings or recesses in the
buttressing wall should be as shown – the
position and shape of the openings should
not impair the lateral support to be given by
the buttressing wall.
3 Refer to Diagram 8 for the rules for
measuring the height of the supported wall.
2C29 Dimensional criteria for openings and
recesses:
The dimensional criteria are given in Diagrams
15 and Table 8.
No openings should be provided in walls below
ground floor except for small holes for services
and ventilation etc. which should be limited to
a maximum area of 0.1m2 at not less than 2m
centres.
2C30 Chases:
a. vertical chases should not be deeper
than 1/3 of the wall thickness or, in cavity
walls, 1/3 of the thickness of the leaf.
b. horizontal chases should not be deeper
than 1/6 of the thickness of the leaf of the wall.
c. chases should not be so positioned as to
impair the stability of the wall, particularly
where hollow blocks are used.
2C31 Overhangs:
the amount of any projection should not impair
the stability of the wall.
Lateral support by roofs and
floors
2C32 A wall in each storey of a building should
extend to the full height of that storey, and
have horizontal lateral supports to restrict
movement of the wall at right angles to its
plane.
2C33 Floors and roofs should:
a. act to transfer lateral forces from walls to
buttressing walls, piers or chimneys, and
b. be secured to the supported wall by
connections specified in paragraphs 2C34 and
2C35.
2C34 The requirements for lateral restraint of
walls at roof and floor levels are given in Table
9 and guidance on satisfying the requirements
is given in paragraphs 2C35 and 2C36.
2C35 Walls should be strapped to floors above
ground level, at intervals not exceeding 2m and
as shown in Diagram 16 by tension straps
conforming to BS EN 845-
resistance purposes, the tension straps should
be material reference 14 or 16.1 or 16.2
(galvanised steel) or other more resistant
Approved Document A Structure
27
SIZES OF STRUCTURAL ELEMENTS A1/2
the buttressing wall, pier or
chimney should provide support
to the full height of the wall
from base to top of wall
See para 2C27
centre line of
buttressing wall
centre line of pier
(alternative arrangement)
centre line
of chimney
centre line
of pier
min
190mm
see
paragraph
2C27
H
T
min 3 x T
min 3 x T
min 2 x T
Diagram 14 Buttressing
Structure Approved Document A
28
A1/2 SIZES OF STRUCTURAL ELEMENTS
See para 2C29
centre line
of butressing
wall, pier or chimney
centre line
of butressing
wall, pier or chimney
outer face of
return wall
H
should not be
greater than
2.1 m
corner of two
L = length of wall external walls
opening
W1
opening
W2
recess
P1 P2 P3 W3
opening
P4 W4 P5
Diagram 15 Sizes of openings and recesses
Span of timber Span of concrete
Span of floor
floor into wall floor into wall
Minimum is parallel max max max max
Nature of Maximum thickness of to wall 4.5m 6.0m 4.5m 6.0m
roof span roof span (m) wall inner (mm)
Value of factor ‘X’
roof spans non 100 6 6 6 6 6
parallel to wall applicable
90 6 6 6 6 5
timber roof 9 100 6 6 5 4 3
spans into wall
90 6 4 4 3 3
Table 8 Value of factor ‘x’ (see diagram 15)
Wall type Wall length Lateral support required
solid or cavity: external any length roof lateral support by every roof forming a junction with the
compartment separating supported wall
greater than 3m floor lateral support by every floor forming a junction with the
supported wall
Internal load-
a compartment or separating wall)
Table 9 Lateral support for walls
Notes
Requirements (refer to Table 6 or values of factor
X).
1 W1 + W2 + W3 should not exceed 2L
3
2 W1 + W2 + W3 should not exceed 3m
3 P1 should be greater than or equal to W1
X
4 P2 should be greater than or equal to W1 + W2
X
5 P3 should be greater than or equal to W2 + W3
X
6 P4 should be greater than or equal to W3
X
7 P5 should be greater than or equal to W4
but should not be less than 665mm. X
8 Take the value of the fact X from Table 6, or it
can be give the value 6, provided the
compressive strength of the bricks or blocks (in
the case of a cavity wall – in the loaded leaf) is
not less than 7N/mm2.
specifications including material references 1
or 3 (austenitic stainless steel). The declared
tensile strength of tension straps should not be
less than 8 kN.
Tension straps need not be provided:
a. in the longitudinal direction of joists in
houses of not more than 2 storeys, if the joists
are at not more than 1.2m centres and have at
least 90mm bearing on the supported walls or
75mm bearing on a timber wall-
end, and
b. in the longitudinal direction of joists in
houses of not more than 2 storeys, if the joists
are carried on the supported wall by joist
hangers in accordance with BS EN 845-
restraint type described in BS 5628: Part 1 and
shown in Diagram 16(c), and are incorporated
at not more than 2m centres, and
c. when a concrete floor has at least 90mm
bearing on the supported wall (see Diagram
16(d)), and
d. where floors are at or about the same
level on each side of a supported wall, and
contact between the floors and wall is either
continuous or at intervals not exceeding 2m.
Where contact is intermittent, the points of
contact should be in line or nearly in line on
plan. (see Diagram 16(e))
2C36 Gable walls should be strapped to roofs
as shown in Diagram 17(a) and (b) by tension
straps as described in 2C35.
Vertical strapping at least 1m in length should
be provided at eaves level at intervals not
exceeding 2m as shown in Diagram 17 (c) and
(d). Vertical strapping may be omitted if the
roof:
a. has a pitch of 15° or more, and
b. is tiled or slated, and
c. is of a type known by local experience to
be resistant to wind gusts, and
d. has main timber members spanning onto
the supported wall at not more than 1.2m
centres.
Approved Document A Structure
29
SIZES OF STRUCTURAL ELEMENTS A1/2
See para 2C35
a. Tension Strap Detail -
c. Restraint Type Joist Hanger d. Restraint by Concrete Floor or Roof
e. Restraint of Internal Walls
Floors should be at or about the
same level on each side of the
wall
Lateral support is continuous where
joists are hard up to the wall
Where joists are not hard up to the wall
blockings at not greater than 2m centres
should be used at the same locations
on both sides of the wall
X X
X to be not less than 90mm
Joist blocked to wall
Noggings, minimum
38mm width to
extend at least 1/2
the depth of the joist
Internal leaf of external
cavity wall or internal wall
requiring lateral restraint
30 x 5mm galvanised mild
steel or other durable strap
at least 1200mm long and
held tight against masonary
wall
30 x 5mm galvanised mild
steel or other durable strap
held tight against masonary
wall and fixed across 3 joists
2m max spacing Diagram 16 Lateral support by floors
Interruption of lateral support
2C37 Where an opening in a floor or roof for a
stairway or the like adjoins a supported wall
and interrupts the continuity of lateral support,
the following conditions should be satisfied for
the purposes of Section 2C:
a. the maximum permitted length of the
opening is to be 3m, measured parallel to the
supported wall, and
b. where a connection is provided by means
other than by anchor, this should be provided
throughout the length of each portion of the
wall situated on each side of the opening, and
c. where connection is provided by mild
steel anchors, these should be spaced closer
than 2m on each side of the opening to provide
the same number of anchors as if there were
no opening, and
d. there should be no other interruption of
lateral support.
Small single-
buildings and annexes
2C38 Size and proportion
(i) General
The guidance given applies in the following
circumstances:-
a. The floor area of the building or annexe
does not exceed 36m2
b. The walls are solidly constructed in
brickwork or blockwork using materials which
comply with paragraphs 2C19 to 2C22.
c. Where the floor area of the building or
annexe exceeds 10m2 the walls have a mass of
not less than 130 kg/m2.
Note: There is no surface mass limitation
recommended for floor areas of 10m2 or less.
d. Access to the roof is only for the
purposes of maintenance and repair.
e. The only lateral loads are wind loads.
Structure Approved Document A
30
A1/2 SIZES OF STRUCTURAL ELEMENTS
See para 2C36 If h is greater than 16pt, provide
restraint here at not greater
than 2 metre centres
Tension strap at highest
point that will provide a
secure connection
Tension straps at
not more than
2 metre centres
(see (b))
each joist fixed to wall-
with framing anchors
or shew nails
gable end wall
strap anchored to
wall and turned
over wall plate
rafter fixed to
wall-
framing anchor
or truss clip
t = sum of thicknesses
of leaves + 10mm
x
h
x/2
x/2
nogging
pack
strap turned over
uncut block
strap anchored
to wall and rafter
a. Tension Strap Location
c. Vertical Strapping
at Eaves-
b. Effective Strapping
at Gable Wall
d. Vertical Strapping
at Eaves-
Diagram 17 Lateral support at roof level
f. The maximum length or width of the
building or annexe does not exceed 9m.
g. The height of the building or annexe does
not exceed the lower value derived from
Diagram 2.
h. The roof is braced at rafter level,
horizontally at eaves level and at the base of
any gable by roof decking, rigid sarking or
diagonal timber bracing, as appropriate, in
accordance with BS 5268 : Part 3.
i. Walls are tied to the roof structure
vertically and horizontally in accordance with
paragraphs 2C32 to 2C36 and with horizontal
lateral restraint at roof level in accordance with
paragraph (iv) below.
j. The roof structure of an annexe is
secured to the structure of the main building at
both rafter and eaves level.
Approved Document A Structure
31
SIZES OF STRUCTURAL ELEMENTS A1/2
See para 2C38
390mm min.
390mm min.
Wall with major
openings
Isolated column
No other openings
in this zone
2.0 m
Diagram 18 Size and location of openings
Notes
1 Major opening should be restricted to
one wall only. Their aggregate width should
not exceed 5.0m and their height should not
be greater than 2.1m
2 There should be no other openings
within 2.0m of a wall containing a major
opening.
3 The aggregate size of openings in a
wall not containing a major opening should
not exceed 2.4m2.
4 There should not be more than one
opening between piers.
5 Unless there is a corner pier the
distance from a window or a door to a
corner should not be less than 390mm.
(ii) Size and location of openings
One or two major openings not more than 2.1m
in height are permitted in one wall of the
building or annexe only. The width of a single
opening or the combined width of two
openings should not exceed 5m.
The only other opening permitted in a building
or annexe are for windows and a single leaf
door. The size and location of these openings
should be in accordance with Diagram 18.
(iii) Wall thickness and recommendations for
piers
The walls should have a minimum thickness of
90mm.
Structure Approved Document A
32
A1/2 SIZES OF STRUCTURAL ELEMENTS
See para 2C38
a. Wall without a Major Opening
b. Wall with a Single Major Opening
c. Wall with Two Major Openings
Bp
Ap Ap
3.0 m max 3.0 m max 3.0 m max
90 mm min
Bp
Bp G
Ap W
Ap
Ap G
Bp
Dotted outline indicates
range of wall positions
Orientation of piers with opening width G not
greater than 2.5 m
Orientation of piers with opening width G greater
than 2.5 m
Dotted outline indicates
range of wall positions
Bp
Ap Cc
Cc
Diagram 19 Wall thickness
Notes
1 In all cases the minimum pier size (Ap
x Bp) should be 390mm x 190mm or 327mm
x 215mm depending on the size of the
masonry units.
2 Isolated column (Case c) to be 325mm
x 325mm minimum (Cc x Cc)
Walls which do not contain a major opening but
exceed 2.5m in length or height should be
bonded or tied to piers for their full height at
not more than 3m centres as shown in Diagram
19a. Walls which contain one or two major
openings should in addition have piers as
shown in Diagrams 19b and 19c. Where ties
are used to connect piers to walls they should
be flat, 20mm x 3mm in cross section, be in
stainless steel in accordance with clause 2C19,
be placed in pairs and be spaced at not more
than 300mm centre vertically.
(iv) Horizontal lateral restraint at roof level
Walls should be tied horizontally at no more
than 2m centres to the roof structure at eaves
level, base of gables and along roof slopes as
shown in Diagram 20 with straps fixed in
accordance with paragraphs 2C35 and 2C36.
Where straps cannot pass through a wall they
should be adequately secured to the masonry
using suitable fixings. Isolated columns should
also be tied to the roof structure (see Diagram
20).
Approved Document A Structure
33
SIZES OF STRUCTURAL ELEMENTS A1/2
Fixing near ridge
position
Key
denotes fixings at eaves level.
denotes fixings at base of gable.
denotes fixings along roof slope.
Note: Fixings should be in accordance with Diagram 17.
Fixing at isolated
column position
See para 2C38
Diagram 20 Lateral restraint at roof level
Height to width relationship
2D1 Where a chimney is not adequately
supported by ties or securely restrained in any
way, its height if measured from the highest
point of intersection with the roof surface,
gutter, etc. should not exceed 4.5W, provided
the density of the masonry is greater than
1500kg/m3, where:
W is the least horizontal dimension of the
chimney measured at the same point of
intersection, and
H is measured to the top of any chimney pot or
other flue terminal.(see Diagram 21)
Section 2D: Proportions for Masonry
Chimneys above the roof surface
Structure Approved Document A
34
A1/2 SIZES OF STRUCTURAL ELEMENTS
H H
W W
See para 2D1
level of highest
point of intersection
Diagram 21 Proportions for masonry
chimneys
Conditions relating to the ground
2E1 There should not be:
a. non-
Digest 427) or wide variation in ground
conditions within the loaded area, nor
b. weaker or more compressible ground at
such a depth below the foundation as could
impair the stability of the structure.
Design provisions
2E2 The following design provisions relate to
foundations:
a. the foundations should be situated
centrally under the wall
b. for foundations in chemically aggressive
soil conditions guidance in BS 8500-
and BRE Special Digest 1 should be followed.
In non-
composed of Portland Cement to BS EN 197 -
1 & 2 and fine and coarse aggregate
conforming to BS EN 12620 and the mix should
comply with one of the following
recommendations:
i. in proportion of 50 kg of Portland cement
to not more than 200kg (0.1m3) of fine
aggregate and 400 kg (0.2 m3) of coarse
aggregate, or
ii. Grade ST2 or Grade GEN I concrete to
BS 8500-
c. minimum thickness T of concrete
foundation should be 15Omm or P, whichever
is the greater where P is derived using Table 10
and Diagram 24. Trench fill foundations may be
used as an acceptable alternative to strip
foundations.
d. foundations stepped on elevation should
overlap by twice the height of the step, by the
thickness of the foundation, or 30Omm,
whichever is greater (see Diagram 22).
For trench fill foundations the overlap should
be twice the height of step or 1 metre,
whichever is greater.
e. steps in foundations should not be of
greater height than the thickness of the
foundation (see Diagram 22).
f. foundation of piers buttresses and
chimneys should project as indicated in
Diagram 23 and the projection X should never
be less than the value of P where there is no
local thickening of the wall.
Minimum width of strip
foundations
2E3 The recommended minimum widths of
foundations given in Table 10 may be used.
Section 2E: Foundations of Plain Concrete
Approved Document A Structure
35
SIZES OF STRUCTURAL ELEMENTS A1/2
See para 2E2d and e
foundations should unite at each
change in level
minimum overlap L = twice height of step, or
thickness of foundation
or 300mm, whichever is greater
S should not be greater than T
(For trench fill foundations,
minimum overlap L = twice height of step,
or 1 metre, whichever
is greater)
T
S
L
Diagram 22 Elevation of stepped
foundation
projection X should not be less than P
See para 2E2f
X
X
P
X
X
Diagram 23 Piers and chimneys
Trench fill foundations may be used as an
alternative to strip foundations.
The minimum thickness
of the foundation (T)
should either be P or
150mm, whichever is
greater
Foundation width
should be not less
than the appropriate
dimension in Table 10
See para 2E2c
Wall should be
central on foundation
P
T
W P
Diagram 24 Foundation dimensions
The table is applicable only within the strict
terms of the criteria described within it.
Minimum Depth of Strip
Foundations
2E4 Except where strip foundations are
founded on rock, the strip foundations should
have a minimum depth of 0.45m to their
underside to avoid the action of frost. This
depth however, will commonly need to be
increased in areas subject to long periods of
frost or in order to transfer the loading onto
satisfactory ground.
In clay soils subject to volume change on
drying (‘shrinkable clays’, with Plasticity Index
greater than or equal to 10%), strip foundations
should be taken to a depth where anticipated
ground movements will not impair the stability
of any part of the building taking due
consideration of the influence of vegetation and
trees on the ground. The depth to the
underside of foundations on clay soils should
not be less than 0.75m although this depth will
commonly need to be increased in order to
transfer the loading onto satisfactory ground.
Structure Approved Document A
36
A1/2 SIZES OF STRUCTURAL ELEMENTS
Total load of load-
Type of Ground
(kN/linear metre)
(including Condition Field test
20 30 40 50 60 70
engineered fill) of ground Applicable Minimum width of strip foundation (mm)
l Not inferior to Requires at least a pneumatic In each case equal to the width of wall
Rock sandstone, limestone or other mechanically operated
or firm chalk pick for excavation
ll Requires pick for excavation. 250 300 400 500 600 650
Gravel or Sand Medium dense Wooden peg 50mm square in cross
section hard to drive beyond 150mm
lll Can be indented slightly by thumb 250 300 400 500 600 650
Clay Stiff
Sandy Clay Stiff
lV Thumb makes impression easily 300 350 450 600 750 850
Clay Firm
Sandy Clay Firm
V Can be excavated with a spade. 400 600
Sand Loose Wooden peg 50mm square in
Silty sand Loose cross section can be easily driven
Clayey sand Loose
Vl Finger pushed in up to 10mm 450 650
Silt Soft
Clay Soft
Sandy clay Soft
Clay or silt Soft
Vll Finger easily pushed in up to 25mm Refer to specialist advice
Silt Very soft
Clay Very soft
Sandy clay Very soft
Clay or silt Very soft
Table 10 Minimum width of strip footings
Note
Foundations on soil types V
and V1 do not fall within the
provisions of this section if the
total load exceeds 30 kN/m.
General
3.1 Wall cladding presents a hazard if it
becomes detached from the building. This
Section provides guidance on the support and
fixing of wall cladding. An acceptable level of
safety can be achieved by different means
depending on the type and location of the
cladding. The guidance given relates to all
forms of cladding, including curtain walling and
glass facades. It is not intended to provide
guidance concerning the weather resistance of
wall cladding which is included in Approved
Document C Site preparation and resistance to
moisture, or guidance on resistance to spread
of fire which is included in Approved Document
B, Fire Safety, or guidance in relation to sound
insulation, which is included in Approved
Document E, Resistance to the Passage of
Sound.
Technical Approach
3.2 The cladding will meet the safety
requirement if:
a. the cladding is capable of safely
sustaining and transmitting to the supporting
structure of the building all dead, imposed and
wind loads, and
b. the cladding is securely fixed to and
supported by the structure of the building. This
shall comprise both vertical support and
horizontal restraint, and
c. provision is made, where necessary, to
accommodate differential movement of the
cladding and the supporting structure of the
building, and
d. the cladding and its fixings (including any
support components) are of durable materials;
the design life of the fixings being not less than
that of the cladding. Fixings shall be corrosion
resistant and of a material type appropriate for
the local environment.
Loading
3.3 Wind loading on the cladding should be
derived from BS 6399, Part 2: 2001 with due
consideration given to local increases in wind
suction arising from funnelling of the wind
through gaps between buildings. Guidance on
funnelling effects is given in BRE Digest 436
Wind loading on buildings -
using BS 6399-
Bucknalls Lane, Garston, Watford, Herts WD2
7JR.
3.4 Where the cladding is required to support
other fixtures e.g. handrails, and fittings, e.g.
antennae and signboards, account should be
taken of the loads and forces arising from such
fixtures and fittings.
3.5 Where the wall cladding is required to
function as pedestrian guarding to stairs,
ramps, vertical drops of 600mm or greater or
as a vehicle barrier, then account should be
taken of the additional imposed loading, as
stipulated in Approved Document K: Protection
from failing, collision and impact.
3.6 Where the wall cladding is required to
safely withstand lateral pressures from crowds,
an appropriate design loading is given in BS
6399 Part 1 and the Guide to Safety at Sports
Grounds (4th Edition, 1997).
Fixings
3.7 The selection of fixings for supporting
cladding should be determined from a
consideration of the proven performance of the
fixing and the risks associated with the
particular application. In this regard
applications should be designated as being
either non-
single fixing could lead to the detachment of
the cladding) or redundant (where failure or
excessive movement of one fixing results in
load sharing by adjacent fixings) and the
required reliability of the fixing determined
accordingly.
Note: Attention is drawn to the availability of
anchors with an ETA (European Technical
Approval) gained in accordance with the
requirements of ETAG 001 Guideline for
European Technical Approval Metal Anchors for
use in Concrete Parts 1-
redundant and non-
Part 6 which covers “Anchors for multiple use
in non-
effectively be regarded as covering redundant
use. The UK definition of “Multiple use” is
contained in an annex to the ETAG Part 6 and
is framed in such a way that all applications
can be validated as to whether or not they
conform to this category without calculation.
All ETAG parts may be downloaded in English
from www.eota.be.
3.8 The strength of fixings should be derived
from tests using materials representative of the
material into which the fixing is to be anchored,
taking account of any inherent weaknesses that
may affect the strength of the fixing, eq. cracks
in concrete due to shrinkage and flexure, or
voids in masonry construction. The design
loads will generally be available from the
manufacturer’s test data determined from a
European Technical Approval (ETA) or an extant
British Standard
Note: ETAS are available which cover use either
in both cracked and non-
non-
both cracked and non-
higher loads for use in non-
cracked concrete. Guidance on how to
Section 3: Wall Cladding
Approved Document A Structure
37
WALL CLADDING A1/2
determine whether a particular concrete
section may be regarded as cracked or noncracked
without reverting to stress calculations
is contained in “Use of anchors with European
Technical Approvals. UK Guidance -
between cracked and non-
This is available on the BBA website
www.bbacerts.co.uk click tab “ETA”.
Further Guidance
3.9 The use of large panels of glass in
cladding of walls and roofs where the cladding
is not divided into small areas by load bearing
framing requires special consideration.
Guidance is given in the following documents:
The Institution of Structural Engineers’ Report
on ‘Structural use of glass in buildings’ dated
1999, available from 11 Upper Belgrave Street,
London SW1X 8BH.
‘Nickel sulfide in toughened glass’ published
by the Centre for Window Cladding and
Technology dated 2000.
3.10 Further guidance on cladding is given in
the following documents -
The Institution of Structural Engineers’ Report
on ‘Aspects of Cladding’ dated 1995.
The Institution of Structural Engineers’ Report
on ‘ Guide to the structural use of adhesives’
dated 1999.
BS 8297 Code of practice for the design and
installation of non-
concrete cladding.
BS 8298 Code of practice for the design and
installation of natural stone cladding and lining.
3.11 Additional guidance on fixings is given in
the following documents -
ETAG No. 001 1997 Guideline for European
Technical Approvals of Metal Anchors for use in
Concrete, European Organisation for Technical
Approvals, (EOTA) Brussels. All EOTA parts may
be downloaded in English from www.eota.be
English version published by the British Board
of Agreement, P 0 Box 195, Bucknalls Lane,
Garston, Watford, Hertfordshire WD25 9BA.
Part 1 Anchors in general
Part 2 Torque controlled anchors
Part 3 Undercut anchors
Part 4 Deformation controlled anchors
Part 5 Bonded anchors
Part 6 Metal anchors for redundant use in
concrete for lightweight systems.
BS 5080 Structural fixings in concrete and
masonry Part 1 1993 : Method of test for
tensile loading.
CIRIA Report RP 566 Cladding Fixings : Good
practice guidance, available from 6 Storey’s
Gate, London SWIP 3AU
CIRIA Reports C579 and C589 Retention of
masonry facades -
Guidance Notes published by the Construction
Fixings Association, c/o Institute of Spring
Technology, Henry Street, Sheffield, South
Yorks S3 7EQ
Guidance Note: Procedure for Site Testing
Construction Fixings (1994)
Guidance Note: European Technical Approvals
for Construction Fixings (1998)
Guidance Note Anchor Selection (1995)
Guidance Note Fixings and Fire (1998)
Guidance Note: Anchor Installation (1996)
Guidance Note: Bonded Anchors (1999)
Guidance Note: Heavy Duty Expansion Anchors
(1997)
Guidance Note: Fixings for Brickwork and
Blockwork (1997)
Guidance Note: Undercut Anchors (1998)
Guidance Note: Fixings and Corosion (2002)
Structure Approved Document A
38
A1/2 WALL CLADDING
Materials
4.1 All materials used to cover roofs, including
transparent or translucent materials, but
excluding windows of glass in residential
buildings with roof pitches of not less than 15°,
shall be capable of safely withstanding the
concentrated imposed loads upon roofs
specified in BS 6399 pt 3.
Recovering of Roofs
4.2 The recovering of roofs is commonly
undertaken to extend the useful life of
buildings. Roof structures may be required to
carry underdrawing or insulation provided at a
time later than their initial construction. This
Section provides guidance on determining
whether such work to a roof constitutes a
material alteration under the Building
Regulations.
4.3 Where the work involves a significant
change in the applied loading the structural
integrity of the roof structure and the
supporting structure should be checked to
ensure that upon completion of the work the
building is not less compliant with requirement
A1 than that of the original building.
4.4 A significant change in roof loading is
when the loading upon the roof is increased by
more than 15%.
4.5 Where such checking of the existing roof
structure indicates that the construction is
unable to sustain any proposed increase in
loading (e.g. due to overstressed members or
unacceptable deflection leading to ponding),
appropriate strengthening work or replacement
of roofing members should be undertaken. This
is classified as a material alteration.
4.6 In carrying out the checks mentioned in
paragraph 4.3 an increase of stress in a
structural member arising from increased
loading does not necessarily indicate that the
roof structure is less compliant than the
original roof provided an adequate factor of
safety is maintained.
4.7 Where work will significantly decrease the
roof dead loading, the roof structure and its
anchorage to the supporting structure should
be checked to ensure that an adequate factor
of safety is maintained against uplift of the roof
under imposed wind loading.
Section 4: Roof Covering
Approved Document A Structure
39
ROOF COVERING A1/2
This Approved Document deals with the
following Requirements which are contained in
the Building Regulations 2000 (as amended by
SI 2001/3335, SI 2002/440, SI 2002/2871 and
SI 2003/2692.
The Requirement
Structure Approved Document A
40
A3 DISPROPORTIONATE COLLAPSE
Disproportionate Collapse
A3. The building shall be constructed so that in the event of an accident
the building will not suffer collapse to an extent disproportionate to the
cause.
Requirement Limits on application
Performance
In the Secretary of State’s view the
Requirement of A3 will be met by an
appropriate choice of measures to reduce the
sensitivity of a building to disproportionate
collapse should an accident occur.
Introduction
0.1 The guidance in Section 5 deals with the
means of meeting this performance criterion.
Guidance
Approved Document A Structure
41
DISPROPORTIONATE COLLAPSE
5.1 The requirement will be met by adopting
the following approach for ensuring that the
building is sufficiently robust to sustain a
limited extent of damage or failure, depending
on the class of the building, without collapse.
a. Determine the Building Class from Table
11
b. For Class 1 buildings -
building has been designed and constructed in
accordance with the rules given in this
Approved Document, or other guidance
referenced under Section 1, for meeting
compliance with requirement A1 and A2 in
normal use, no additional measures are likely
to be necessary.
c. For Class 2A buildings -
effective horizontal ties, or effective anchorage
of suspended floors to walls, as described in
the Codes and Standards listed under
paragraph 5.2 for framed and load-
construction; the latter being defined in
paragraph 5.3 below.
d. For Class 2B buildings -
effective horizontal ties, as described in the
Codes and Standards listed under paragraph
5.2 for framed and load-
construction; (the latter being defined in
paragraph 5.3 below), together with:
– effective vertical ties, as defined in the
Codes and Standards listed under
Section 5: Reducing the sensitivity of the
building to disproportionate collapse in the
event of an accident
Structure Approved Document A
42
A3 DISPROPORTIONATE COLLAPSE
Class Building Type and Occupancy
1 Houses not exceeding 4 storeys.
Agricultural buildings
Buildings into which people rarely go, provided no part of the building is closer to another building, or area where
people do go, than a distance of 1.5 times the building height
2A 5 storey single occupancy houses
Hotels not exceeding 4 storeys
Flats, apartments and other residential buildings not exceeding 4 storeys
Offices not exceeding 4 storeys
Industrial buildings not exceeding 3 storeys
Retailing premises not exceeding 3 storeys of less than 2000m2 floor area in each storey
Single storey educational buildings
All buildings not exceeding 2 storeys to which members of the public are admitted and which contain floor areas not
exceeding 2000m2 at each storey
2B Hotels, flats, apartments and other residential buildings greater than 4 storeys but not exceeding 15 storeys
Educational buildings greater than 1 storey but not exceeding 15 storeys
Retailing premises greater than 3 storeys but not exceeding 15 storeys
Hospitals not exceeding 3 storeys
Offices greater than 4 storeys but not exceeding 15 storeys
All buildings to which members of the public are admitted which contain floor areas exceeding 2000m2 but less than
5000m2 at each storey
Car parking not exceeding 6 storeys
3 All buildings defined above as Class 2A and 2B that exceed the limits on area and/or number of storeys
Grandstands accommodating more than 5000 spectators
Buildings containing hazardous substances and/or processes
NOTE 1: For buildings intended for more than one type of use the Class should be that pertaining to the most onerous type.
NOTE 2: In determining the number of storeys in a building, basement storeys may be excluded provided such basement storeys
fulfil the robustness requirements of Class 2B buildings.
Table 11 Building Classes
paragraph 5.2, in all supporting columns
and walls, or alternatively,
– check that upon the notional removal of
each supporting column and each beam
supporting one or more columns, or any
nominal length of load-
at a time in each storey of the building)
that the building remains stable and that
the area of floor at any storey at risk of
collapse does not exceed 15% of the
floor area of that storey or 70m2,
whichever is smaller, and does not
extend further than the immediate
adjacent storeys (see Diagram 25).
Where the notional removal of such columns
and lengths of walls would result in an extent
of damage in excess of the above limit, then
such elements should be designed as a “key
element” as defined in paragraph 5.3 below.
e. For Class 3 buildings -
assessment of the building should be
undertaken taking into account all the normal
hazards that may reasonably be foreseen,
together with any abnormal hazards.
Critical situations for design should be selected
that reflect the conditions that can reasonably
be foreseen as possible during the life of the
building. The structural form and concept and
any protective measures should then be
chosen and the detailed design of the structure
and its elements undertaken in accordance
with the recommendations given in the Codes
and Standards given in paragraph 5.2.
5.2 Details of the effective horizontal and
vertical ties, together with the design
approaches for checking the integrity of the
building following the notional removal of
vertical members and the design of key
elements, are available in the following Codes
and Standards:
BS5628: Part 1 – Structural use of unreinforced
masonry
BS5950: Part 1 – Structural use of steelwork
in building
BS8110: Part 1 – Structural use of plain,
reinforced and prestressed concrete.
BS8110: Part 2 – ditto
5.3 Definitions
Nominal length of load-
The nominal length of load-
construction referred to in 5.1d should be
taken as follows :
– in the case of a reinforced concrete wall,
the distance between lateral supports
subject to a maximum length not
exceeding 2.25H.
– in the case of an external masonry wall,
or timber or steel stud wall, the length
measured between vertical lateral
supports.
– in the case of an internal masonry wall, or
timber or steel stud wall, a length not
exceeding 2.25H.
– where H is the storey height in metres.
Key Elements
A “key element”, as referred to in paragraph
5.1d, should be capable of sustaining an
accidental design loading of 34 kN/m2 applied
in the horizontal and vertical directions (in one
direction at a time) to the member and any
attached components (eg cladding etc.) having
regard to the ultimate strength of such
components and their connections. Such
accidental design loading should be assumed
to act simultaneously with 1/3 of all normal
characteristic loading (i.e. wind and imposed
loading).
Load-
For the purposes of this Guidance the term
“load-
masonry cross-
comprising close centred timber or lightweight
steel section studs.
Alternative Approach
5.4 Alternatively, for any building which does
not fall into the classes listed under Table 11 or
for which the consequences of collapse may
warrant particular examination of the risks
involved, the performance may be met by the
recommendations given in the following
Reports:
“Guidance on Robustness and Provision
against Accidental Actions” dated July,1999,
together with the accompanying BRE Report
No. 200682
“Calibration of Proposed Revised Guidance on
meeting Compliance with the Requirements of
Building Regulation Part A3.
Both of the above documents are available on
the following ODPM web-
http://www.odpm.gov.uk
Approved Document A Structure
43
DISPROPORTIONATE COLLAPSE A3
Structure Approved Document A
44
A3 DISPROPORTIONATE COLLAPSE
area at risk of collapse
limited to 15% of the
floor area of that storey
or 70m2, whichever is
the less, and does not
extend further than the
immediate adjacent
storeys.
Plan Section
See para 5.1d
Diagram 25 Area at risk of collapse in the event of an accident
A1/2
BS 187 : 1978 Specification for calcium
silicate (sandlime and
flintlime) bricks
Amendment slip
1. AMD 5427
BS 1243:1978 Specification for metal ties for
cavity wall construction
Amendment slips
1. AMD 3651
2. AMD 4024
BS 3921:1985 Specification for clay bricks
Amendment slip
1. AMD 8946
BS 5080: Structural fixings in concrete
and masonry
Part 1 : 1993 Method of test for tensile
loading
BS 5268: Structural use of timber
Part 2: 2002 Code of practice for
permissible stress design,
materials and workmanship
Part 3: 1998 Code of practice for trussed
rafter roofs.
BS 5390:1976 Code of practice for stone
masonry
Amendment slip
1. AMD 4272
BS 5628: Code of practice for use of
masonry
Part 1: 1992 Structural use of unreinforced
masonry
Amendment slip
1. AMD 7745
2. AMD 13680
Part 2: 2000 Structural use of reinforced
and prestressed masonry
Part 3: 2001 Materials and components,
design and workmanship
BS 5950: Structural use of steelwork in
building
Part 1: 2000 Code of practice for design.
Rolled and welded sections.
Amendment slip
1. AMD 13199
Part 2:2001 Specification for materials,
fabrication and erection.
Rolled and welded sections.
Part 3 : Design in composite
construction
Section 3.1: 1990 Code of practice for design
of simple and continuous composite beams.
Part 4: 1994 Code of practice for design of
composite slabs with profiled
steel sheeting.
Part 5: 1998 Code of practice for design of
cold formed thin gauge
sections.
BS 6073: Precast concrete masonry
units
Part 1: 1981 Specification for precast
concrete masonry units
Amendment slips
1. AMD 3944
2. AMD 4462
BS 6399: Loading for buildings :
Part 1: 1996 Code of practice for dead and
imposed loads
Amendment slip
1. AMD 13669
BS 6399: Loading for buildings :
Part 2: 1997 Code of practice for wind
loads
Amendment slip
1. AMD 13392
2. AMD 14009
BS 6399: Loading for buildings
Part 3 :1988 Code of practice for imposed
roof loads.
Amendment slip
1. AMD 6033
2. AMD 9187
3. AMD 9452
BS 6649: 1985 Specification for clay and
calcium silicate modular
bricks
BS 8002: 1994 Code of practice for earth
retaining structures
BS 8004: 1986 Code of practice for
foundations.
Amendment slip
1. AMD 8851
2. AMD 12062
3. AMD 13386
BS 8103: Structural design of low-
buildings :
Part 1: 1995 Code of practice for stability,
site investigation, foundations
and ground floor slabs for
housing.
Amendment slip
1. AMD 8980
Part 2: 1996 Code of practice for masonry
walls for housing
Part 3: 1996 Code of practice for timber
floors and roofs for housing.
Part 4: 1995 Code of practice for
suspended concrete floors for
housing
BS 8110: Structural use of concrete
Part 1: 1997 Code of practice for design
and construction
Amendment slip
1. AMD 9882
2. AMD 13468
Approved Document A Structure
45
STANDARDS REFERRED TO A
Part 2: 1985 Code of practice for special
circumstances
Amendment slip
1. AMD 5914
2. AMD 12061
Part 3: 1995 Design charts for singly
reinforced beams, doubly
reinforced beams and
rectangular columns.
Amendment slip
1. AMD 5918
BS 8118: Structural use of aluminium
Part 1: 1991 Code of practice for design
Amendment slip
1. AMD 10485
Part 2: 1991 Specification for materials,
workmanship and protection
Amendment slip
1. AMD 10486
BS 8297: 2000 Code of practice for design
and installation of nonloadbearing
precast concrete
cladding.
Amendment slip
1. AMD 11064
2. AMD 13018
BS 8298: 1994 Code of practice for design
and installation of natural
stone cladding and lining
BS 8500: Concrete. Complementary
British Standard to BS EN
206-
Part 1:2002 Method of specifying and
guidance for the specifier
Part 2:2002 Specification for constituent
materials and concrete
BS EN 197 Cement
Part 1:2000 Composition, specifications
and conformity criteria for
common elements
Part 2:2000 Conformity evaluation
BS EN 771 Specification for Masonry
Units
Part 1 :2003 Clay masonry units
Part 2 :2001 Calcium silicate masonry
units
Part 3 : Aggregate concrete masonry
units [in preparation]
Part 4 : 2001 Autoclaved aerated concrete
masonry units
Part 5 : Manufactured stone masonry
units [in preparation]
Part 6 : 2001 Natural stone masonry units
BS EN 845 Specification for ancillary
components for masonry
Part 1 : 2001 Ties, tension straps, hangers
and brackets
Part 2 : 2001 Lintels
Part 3 : 2001 Bed joint reinforcement of
steel meshwork
BS EN 998 Specification for mortar for
masonry
Part 2 :2002 Masonry mortar
BS EN 12620: Aggregates for concrete
2002
DD140-
and timber frame connections
DD140-
of wall ties
A3
BS 5628: Code of practice for use of
masonry
Part 1: 1992 Structural use of unreinforced
masonry
Amendment slip
1. AMD 7745
2. AMD 13680
BS 5950: Structural use of steelwork in
building
Part 1: 2000 Code of practice for design.
Rolled and welded sections.
Amendment slip
1. AMD 13199
BS 8110: Structural use of concrete
Part 1: 1997 Code of practice for design
and construction
Amendment slip
1. AMD 9882
2. AMD 13468
Part 2: 1985 Code of practice for special
circumstances
Amendment slip
1. AMD 5914
2. AMD 12061
Structure Approved Document A
46
STANDARDS REFERRED TO
The following documents have been approved
and issued by the Secretary of State for the
purpose of providing practical guidance with
respect to the requirements of the Building
Regulations 2000 (as amended).
Approved Document A – Structure: 2004
Edition
Approved Document B – Fire safety: 2000
Edition, amended 2000 and 2002
Approved Document C – Site preparation and
resistance to moisture: 1992 Edition, second
impression (with amendments) 1992, further
amended 2000
Approved Document D – Toxic substances:
amended 1992, further amended 2000
Approved Document E – Resistance to the
passage of sound: 2003 Edition
Approved Document F – Ventilation: 1995
Edition, amended 2000
Approved Document G – Hygiene: 1992
Edition, second impression (with amendments)
1992, further amended 2000
Approved Document H – Drainage and waste
disposal: 2002 Edition
Approved document J – Combustion
appliances and fuel storage systems:
2002 Edition
Approved Document K – Protection from
falling, collision and impact: 1998 Edition,
amended 2000
Approved document L1 – Conservation of fuel
and power in dwellings: 2002 Edition
Approved document L2 – Conservation of fuel
and power in buildings other than dwellings:
2002 Edition
Approved Document M – Access and facilities
for disabled people: 2004 Edition
Approved Document N – Glazing -
relation to impact, opening and cleaning: 1998
Edition, amended 2000
Approved Document to support regulation 7
– materials and workmanship: 1999 Edition,
amended 2000
Approved Document A Structure
47
Approved Documents
APPROVED DOCUMENTS
Building Regulations 2000 APPROVED DOCUMENT A Structure
© Crown Copyright 2004.
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For any other use of this material please write to The HMSO Licensing Division, HMSO, St Clements House, 2–16 Colegate, Norwich NR3 1BQ.
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