Hangin Calculation

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domestic structure SBSG 2007

ANNEX C

Small buildings structural guidance

1.A General

1.B Stability

1.C Foundations

1.D Masonry walls

1.E Timber frame walls

1.F Timber floor and roofmembers

contents


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domestic structure SBSG annex 1.A 2007


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Annex

1.A General

1.A.0 Introduction1.A.1 Scope1.A.2 Revisions to small buildings guide1.A.3 New guidance1.A.4 Explanation of terms1.A.5 Rules of measurement for storeys, walls , panels and building heights

Contents


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annex

1.AGeneral

1.A.0 IntroductionThe Small Buildings Structural Guidance (SBSG) which is contained within Annexes 1.A-F has beenprepared to provide structural guidance to designers of small domestic buildings on how to meetStandard 1.1.

The buildings covered by this guidance are restricted in terms of construction type, size and subsoilconditions to those commonly occurring in Scotland.

This guidance has been written for those with expertise in building design and construction but notnecessarily in structural engineering design. Where the conditions or parameters fall outside thescope then specialist advice should be sought from chartered engineers with the appropriate skillsand experience.

This guidance replaces the Small Buildings Guide Second Edition 1994 and has been prepared inconsultation with ODPM and DFP Northern Ireland so that reasonably uniform solutions might beadopted towards meeting the requirements of the respective structural regulations and to incorporatea broader base of experience into the definition of standards.

1.A.1 ScopeThis guidance covers the following types ofbuildings-a. Buildings with masonry walls

domestic buildings of not more than 3 storeys without basement storeys

extensions with eaves height not more than 3m to low rise domestic buildings includinggarages and outbuildings;

single storey, single skin buildings forming a garage or outbuilding within the curtilage of a

dwellingb. Buildings with timber frame walls

domestic buildings of not more than 2 storeys without basement storeys

extensions with eaves height not more than 3m to low rise domestic buildings

The full description of the types ofbuildings and restrictions to which this guidance is applicable is setout within the scope of each of the annexes.

It recommended that prior to using the SBSG for particularworks , the scope of the works should bechecked against all of the limitations on its use to ensure that it is appropriate in the circumstances.and in particular :Annex 1C: Foundations : Geotechnical conditionsAnnex 1D: Masonry walls : Not more than 3 storeys

Maximum building height of 15 mMaximum 12m length between supporting wallsWind speed verses the allowable height ofbuildingOpenings in walls not more than 3 m in length

Annex 1.E: Timber frame walls Not more than 2 storeysMaximum building height of 10 mMaximum 10m length between supporting wallsWind speed verses the allowable height ofbuildingOpenings in walls totalling not more than 30% of the wallarea

Annex 1F: Timber floor and roofmembers Floor spans not exceeding 5.4 m

Roofspans not exceeding 6 mRaised Tie and Collared Roofs only for attic storageloading


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Design and construction will also have to comply with all other relevant building standards

Annex 1.B gives general rules on stability which should be observed in Annexes 1.E-F whereasAnnexes 1.C and 1.E -F should not be used independently of each other.

1.A.2 Revisions to Small Buildings GuideThe Small Buildings Guide has been revised and updated to Small Buildings Structural Guidanceincorporating changes in construction practice specifically;

Loadings

Wind loading on traditional dwellingsProposed revision of the simplified roofsnow load map for ScotlandMasonry walls

More detailed guidance on openings

More detailed guidance on lateral support

Differences in ground levels either sides of walls

Stainless steel wall ties to be used in all locationsTimber Floor and Roof MembersThe timber span tables have been expanded to cover raised tie and collared roofs.

1.A.3 Timber frame constructionTimber frame construction has been a significant form ofconstruction fordomestic buildings for over20 years in Scotland ,rising from 38% of new starts in 1984 in the volume housing market to over 63% in 2004, and a large proportion of the single build and extension market. Although the guidance inthe Small Buildings Guide was restricted to traditional masonry construction as timber frameconstruction has been used and accepted for over 30 years it was considered necessary to extendthe scope of the guidance for small buildings to include timber frame walls.

The timber frame wall guidance has been restricted to masonry clad platform frame constructionwhich is the most common form ofconstruction.

1.A.4 Explanation of Terms

The following terms are used in the SBSG in addition to the definitions and explanation of terms inAppendix A of the Technical Handbooks.Buttressing wall means a wall designed and constructed to afford lateral support to another wallperpendicular to it, support being provided from the base to the top of the wall.Cavity width means the horizontal distance between the two leaves of a cavity wall.Piermeans a member which forms an integral part of a wall, in the form of a thickened section atintervals along the wall so as to afford lateral support to the wall to which it is bonded or securely tied.Spacing means the distance between the longitudinal centres of any two adjacent timber members ofthe same type, measured in the plane of floor, ceiling or roofstructure of which the members form apart.Span means distance measured along the centre line of a member between the centres of any twoadjacent bearings or supports. Note: The spans given in Annex 1.E for Cripple Studs and Lintels andin Annex 1.F for floor joists, and roof joists are the clear spans, i.e. spans between the faces of thesupports.Supported wall means a wall to which lateral support is afforded by a combination of buttressingwalls, piers orchimneys acting in conjunction with floors orroof.Engineered fill means fill that is selected, placed and compacted to an appropriate specification inorder that it will exhibit the required engineering behaviour .Normally such fill would not have takenplace prior to development of the site allowing the necessary control over the type of fill material andmethod of placement to be exercised.Non-engineered fill means fill that has arisen as a by-product of human activity, usually involving thedisposal of waste materials. Normally such fill would occur on sites where uncontrolled filling hastaken place and therefore no reliance can be placed on the type of fill material and method of

placement and hence its ability to support the buildings.


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1.A.5 Rules of measurement for storeys , walls , panels and building heightsThe height of a wall or a storey should be measured in accordance with the following diagram.

H3

H2H1

line of lateral

support to gable

at ceiling levelundersideofroof

joist

2.7m

max

2.7m maxTop of foundations

H P

AA1

=

line of base

of gable

B

D

C B1top ofwall orbase ofparapet

parapet=

line of top of gable

line of lateralsupport to gable

wall along roof slope

=

=

2.7mm

ax

2.7mm

ax

base of wall

ground level

Panelheight

Floor

deckthickness

h

eadbinderthickness

Pan

elheight

floordeckthickness

panel height

floor joist

panel height

Key

(a) Measuring storey heightsA is theground storeyheight if the ground floor is a suspended timber floor or a structurally separate

ground floor slab

A1 is theground storeyheight if the ground floor is a suspended concrete floor bearing on the external

wall

B is the intermediate storeyheight providing

B1 is the top storeyheight for walls which do not include a gable

C is the top storeyheight where lateral support is given to the gable at both ceiling level and along the

roofslope

D is the top storeyheight for walls which include a gable where lateral support is given to the gable

only along the roofslope

(b) Measuring wall heights

H1is the height of a wall that does not include a gable

H2is the height of a compartmentor a separating wallwhich may extend to the under side of the roof.

H3is the height for a wall(except a compartmentor separating wall) which includes a gable

P is the height of a parapet. If the parapet height is more than 1.2m add the height to H1(c) Measuring timber panel heights

Panel heights are measured from the underside of the bottom rail to the top of the top rail

(d) Measuring building height

Buildingheights are measured from the lowest finished ground level to the highest point of the roof


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domestic structure SBSG annex 1.B 2007

Annex1.B Stability

1.B.0 Introduction1.B.1 Stability recommendations1.B.2 Timber roof bracing

Contents


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domestic structure SBSG annex 1.B 2007

annex

1.BBasic requirements for stability

1.B.0 IntroductionBuildings should be stable under the likely combinations of dead , imposed and wind loadingconditions in terms of the individual structural elements , their interaction together and overall stabilityas a structure .This Annex provides guidance on the principles of stability and provisions which should be taken withrespect to all forms ofbuildings within the scope of the SBSG.

1.B.1 Stability recommendationsThe following provisions should be made to ensure the stability of the building :a. the overall size and proportioning of the building should be limited in accordance with the specific

guidance for each form ofconstruction;b. a suitable layout of walls (both internal and external) forming a robust three dimensional box

structure in plan should be constructed with restrictions on the maximum size of cells measured inaccordance with the specific guidance for each form ofconstruction;

c. the internal and external walls should be adequately connected by either masonry bonding or byusing mechanical connections;

d. the intermediate floors and roofshould be of such construction and interconnection with the wallsthat they provide local support to the walls and also act as horizontal diaphragms capable oftransferring the wind forces to buttressing elements of the building.

More detailed guidance is provided in Annexes 1.B-1.E

1.B.2 Timber roof bracingTrussed rafterroofs should be braced in accordance with the recommendations of BS 5268: Part 3:1998 .

A traditional cut timberroof(i.e. using rafters, purlins and ceiling joists) generally has sufficient built-inresistance to instability and wind forces (e.g. from either hipped ends, tiling battens, rigid sarking, orthe like). However, diagonal rafter bracing equivalent to that recommended in BS 5268: Part 3: 1998or Annex H of BS 8103: Part 3: 1996 for trussed rafter roofs, should be provided particularly forsingle-hipped and non-hipped roofs of more than 40 pitch to detached houses.


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domestic structure SBSG annex 1.C 2007

Annex1.C Foundations

1.C.0 Introduction1.C.1 Conditions related to the subsoil1.C.2 Design recommendations1.C.3 Eccentric foundations1.C.4 Extensions to existing buildings1.C.5 Minimum width of strip foundations

Contents


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annex

1.CFoundations

1.C.0 IntroductionThe dead , imposed and live loads are transmitted from the building to the subsoil by means of thefoundations which should be designed taking into account the loadings and the subsoil conditionswithout undue settlement .This Annex provides guidance on suitable subsoil conditions on which buildings within the scope ofthe SBSG can be constructed, the precautions to be taken and guidance on simple foundations forsuch buildings.

1.C.1 Conditions related to the subsoilThe subsoil conditions should be adequate where there is no -

non- engineered fill or wide variation in type of subsoil within the loaded area; or

peat within the loaded area; or

a weaker type of soil within the loaded area at such a depth below the soil on which the foundationrests as could impair the stability of the building

The minimum depth to the underside offoundations should be determined on the basis of the greatestof:

the depth to selected bearing stratum;

a depth of 450 mm to the underside offoundations .This should avoid damage from frost action innormal soil conditions although this depth may have to be increased in areas which are subject tolong periods of frost or in order to transfer the loading onto satisfactory ground.

depth of 600 mm to the underside offoundations where clay soils are present although this depthwill commonly need to be increased in order to transfer the loading onto satisfactory ground.

The susceptibility of ground to movement, action of frost and changes in water table varies widely andthe advice of a structural engineer should be sought if the conditions are outwith the parameters setout above. More detailed guidance is provided in BRE Digests 240 and 241.

1.C.2 Design recommendationsThe design offoundations should be adequate where all of the following are followed -a. the foundations are situated centrally under the wall( except as in clause 1.C.3);b. the strip foundations have the minimum widths given in the table to 1.C.5;c. concrete in chemically non-aggressive soils is composed of Portland Cement to BS EN 197-1 & 2:

2000 and fine and coarse aggregate conforms to BS EN 12620:2002 and the mix complies withone of the following recommendations:

in proportion of 50 kg of Portland cement to not more than 100kg(0.05m3) of fine aggregate and 200 kg (0.1m3) of coarse aggregate, or

Grade ST2 or Grade GEN I concrete to BS 8500-2d. in chemically aggressive soils guidance is provided in BS 8500-1: Part 1 and

BRE Special Digest 1.e. For strip foundations, the foundation width should not be less than the appropriate dimension , WF

in table to 1.C.5


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f. the minimum thickness, T, of the concrete foundation is 150 mm or the scarcement width, P;whichever is the greater, where P is derived using the table to 1.C.5 and the diagram below.Trench fill foundations may be used as an acceptable alternative to strip foundations.

g. footings with regular offsets should have a depth at least 1.33 times the respective projection P1(see diagram 1.7.2 opposite); with the overall width not less than the sum of , WF from table to1.C.5 plus offset dimensions A1 and A2 and walls should be central on the foundation

h. forfoundations stepped in elevation

height of steps, S, should not be of greater height than the foundation thickness, T

overlap, L, should be the greater of twice the step height ,S, the foundation thickness, T, or 300mm

.

.

.

P P

.

T

WT

WF

..

.

T

PP A1 WT A2

P1

1.33 P min1

W + A + AF 1 2

L

L = greater of 2 x S, T, 300mm

S

T

i. and chimneys should project as shown in the diagram belowwhere X must be not less than Pfoundations for piers , buttresses

X

X

X

P


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1.C.3 Eccentric foundationsa. This guidance and the diagram opposite is limited to:

single storey buildings of 4.5 m maximum heightwhere a wall is to be constructed either against a

boundary or against an existing wall where it is notpossible to construct the wall centrally on thefoundation.

masonry cavity or timber frame walls with masonryouter leaf with either a flat or pitched roof

similar good ground conditions below both theexisting and new foundations

the foundations should comply with all of the clausesof this Annex (i.e. minimum foundation depththickness and width ,concrete grade (Grade ST2 orGEN I) and the range of normal subsoil conditionsstated) .

b. Where the wall and its foundation is to be constructedagainst an existing wall then the foundation shouldcomply with 1.C. 4 below

c. the full width of the foundation, WF (from Table 1.C.5) isnot effective in transmitting the load to the soil, and onlya proportion of the width is effective. This effective widthof the foundation, WF' is determined from

WF' = WF (2 e)where e is the eccentricity of the resultant thrust R dueto the wall load, about the centre-line of the foundation.

d. Nonetheless, the minimum foundation width,WF, shouldstill be read directly from Table 1.C.5.

e. the minimum foundation thickness, T for the minimumfoundation widths listed in Table 1.C.5 should be takenas 200mm.

f. an appropriate steel reinforcement mesh, (e.g. A142),should be placed at 50mm cover from the base of thefoundation.

.WT

e

R

WF'

WF

T


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1.C.4 Extensions to existing buildingsa. This guidance and the diagram opposite is limited to:

extensions of not more than two storeys connected toexisting buildings

extensions with masonry cavity or timber frame walls with

masonry outer leaf with either a flat or pitched roof similar ground conditions below both the existing and new

foundations in range types I-VI from Table to 1.C.5

the extension foundations should comply with all of theclauses of this Annex (i.e. minimum foundation depththickness and width ,concrete grade (Grade ST2 or GENI) and the range of normal subsoil conditions stated) .

b. Where the depth of the existing foundations is less than thatin 1.C.1, the depth of the extension foundation shouldmatch that of existing foundation depth at the interface andstep down progressively to that of 1.C.1.

e. To minimise the occurrence of differential settlement

between the extension and the existing structure, thefollowing should be considered;

movement joints should be placed between the existingand new foundations, and walls to accommodate anydifferential settlement between the extension andexisting building .

on non-compressible soils and rock (Soil types I, II andIII in Table 1.C.5) the strip foundation widths listed in thetable should be adopted and the new foundation shouldbe placed at the same depth as the existing foundation,

On soils of medium compressibility (Soil types IV, V andVI in Table 1.C.5) the foundation dimensions should belarge enough so that excessive settlement is avoided byincreasing the minimum width ,WF, by 25% from thevalues listed in Table 1.C.5 to lower the bearingpressure on the soil, recognising that foundations on soiltypes V and VI do not fall within the provisions of thisannex if the total load exceeds 30 kN/m.

To reach less compressible soil, the new foundationmay be placed at a greater depth than the existingfoundation. In such a case extreme care must be takento ensure that stability of the existing foundation ismaintained during excavation for the new foundation.

The design of an appropriate foundation on highlycompressible soils (Soil type VII in Table 1.C.5) isbeyond the scope of this annex and specialist adviceshould be sought for such cases.

Additional information is provided in BRE GBG 53Foundations for low-rise building extensions

Where the subsoil to the existing building has beensubjected to ground improvement techniques ( e.g.vibrocompaction , underpinning , soil replacement etc )then specialist advice should be sought from charteredengineers with the appropriate skills and experience.

existingwalls

new wall

movement joint betweenexisting and new wallsand foundations

new foundationfor extension

existingfoundation

floor

existing wall

movement joint

new wall

Existing WallNew Walls

Brick ties and

channels allowing

vertical movement


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1.C.5 Minimum width of strip foundationsThe recommended widths offoundations set out in the table below may be used subject to :

the subsoil conditions in 1.C.1,

the foundation design provisions in 1.C.2

the type and condition of subsoil is known and is within the types set out in the Table below, the loading at the base of the wall is within acceptable limits.

The table is applicable only within the strict terms of the criteria described within it and where thesubsoil is not covered by the types set out below or the total load from the load-bearing wallingexceeds 70kN/linear metre or 30kN/linear metre in types of subsoil under heads V-VI or type VIIsubsoil below, then a designed foundation may be required and the advice of a structural engineershould be sought.Minimum width of strip footings

Total load of load-bearing walling notmore than (kN/linear metre)20 30 40 50 60 70Type of

Ground(includingengineeredfill)

Condition

of ground

Field Test Applicable

Minimum width of strip foundation,WF (mm)

I Rock Notinferior tosandstone,limestoneor firmchalk

Requires at least a pneumaticor other mechanically operatedpick for excavation

In each case equal to the width of wall

II Gravel orSand

Mediumdense

Requires pick for excavation.Wooden peg 50mm square incross section hard to drivebeyond 150mm

250 300 400 500 600 650

III ClaySandy Clay

StiffStiff

Can be indented slightly bythumb

250 300 400 500 600 650

IV ClaySandy Clay

FirmFirm

Thumb makes impressioneasily

300 350 450 600 750 850

V SandSilty sandClayey sand

LooseLooseLoose

Can be excavated with aspade. Wooden peg 50mmsquare in cross section can beeasily driven

400 600

VI Silt

ClaySandy clayClay or silt

Soft

SoftSoftSoft

Finger pushed in up to 10mm 450 650

NoteFoundations on soil typesV and V1 do not fall

within the provisions ofthis annex if the total loadexceeds 30kN/m.

VII SiltClaySandy clayClay or silt

Very softVery softVery softVery soft

Finger easily pushed in up to25mm

Refer to specialist advice


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domestic structure SBSG annex 1.D 2007

Annex1.D Masonry walls

1.D.0 Introduction1.D.1 Wall types1.D.2 Conditions relating to the Building of which the walls forms part1.D.3 Maximum floor area1.D.4 Imposed loads on roofs , floors and ceilings

Thickness of walls1.D.5 General1.D.6 Solid external walls, compartment walls and separating walls in coursed brickwork or

blockwork1.D.7 Solid external walls, compartment walls and separating walls in uncoursed stone , flints

etc1.D.8 Cavity walls in coursed brickwork and blockwork1.D.9 Walls providing vertical support to other walls1.D.10 Internal load-bearing walls in brickwork or blockwork1.D.11 Parapet walls

1.D.12 Single leaf external walls1.D.13 Modular bricks and bricks1.D.14 Maximum height of buildings based on wind loadings1.D.15 Maximum allowable length and height of the wall

Construction materials and workmanship1.D.16 Wall ties1.D.17 Brick and block construction1.D.18 Compressive strength of masonry units1.D.19 Declared compressive strength of masonry units1.D.20 Normalised compressive strength of masonry units1.D.21 Compressive strength of masonry units in walls1.D.22 Mortar

1.D.23 Lintels for openingsLoading on walls

1.D.24 Maximum span of floors1.D.25 Other loading conditions

End restraint1.D.26 Vertical lateral restraint to walls1.D.27 Criteria for buttressing walls1.D.28 Criteria for piers and chimney providing restraint

Openings , recesses , chases and overhangs1.D.29 General1.D.30 Dimensional criteria for openings and recesses1.D.31 Sizes of openings and recesses

1.D.32 Chases1.D.33 Overhangs1.D.34 Lateral support by roofs and buildings1.D.35 Gable wall strapping1.D.36 Interruption of lateral support1.D.37 Movement in masonry

Small single storey , single skin buildings1.D.38 General1.D.39 Size and proportions of openings1.D.40 Wall thicknesses and piers1.D.41 Horizontal lateral restraint at roof level1.D.42 Proportions for masonry chimneys

Contents


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annex

1.DMasonry walls

1.D.0 IntroductionSmall buildings of traditional masonry walls can be designed to take advantage of custom andpractice to provide designs taking into account loading conditions , limitations on dimensions ,openings and subject to , restraint conditions .This Annex provides guidance for traditional masonry wall construction for the following building typesa. domestic buildings of not more than 3 storeys where loading criteria for individual floors does not

exceed those given in 1.D.4 and total limit of loading does not exceed that given in 1.D.25;b. single storey single skin extensions to domestic buildings including garages and outbuildings that

do not exceed the dimensional criteria set out in 1.D.2b ; and.d. single storey , single skin buildings forming a garage or outbuilding within the curtilage of adwelling that do not exceed the dimensional criteria set out in 1.D.2c

1.D.1 Wall typesThis Annex deals only with the types of wall extending to full storey height set out below and parapetwalls.a. Domestic buildings of up to 3 storeys

External walls

Internal load bearing walls

Separating wallsb. Extensions to domestic buildings and single storeybuildings

External walls


This annex should be used in conjunction with Annexes 1.B ;anda. if wall thickness is to be determined according to 1.D.5 to 1.D.13 all appropriate design conditionsgiven in this Annex should be satisfied;b. walls should comply with the relevant requirements of BS 5628: Part 3: 2001, except as regardsthe conditions given in 1.D.2 and 1.D. 3 -4,1.D.14-41;c. in formulating the guidance of this Annex, the worst combination of circumstances likely to arisewas taken into account.d. If a requirement of this Annex is considered too onerous in a particular case then adequacy bycalculation should be shown in respect of the aspect of the wall which is subject to the departurerather than for the entire wall;e. the guidance given in this Annex is based upon unit compressive strengths of bricks and blocks

being not less than that indicated in the Tables to 1.D.19-20 and diagrams to 1.D.21f. BS5628 Part 1; 1992 gives design strengths for walls where the suitability for use of masonry

units of other compressive strengths are being considered.


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1.D.2 Conditions relating to the Building of which the walls forms partThis Annex applies only to buildings having proportions within the following limits and as shownon the Diagrams below subject to the limits of 1.D.15a. domestic buildings of not more than three storeys

the maximum height of the building measured from the lowest finished ground leveladjoining the building to the highest point of any wall orroofshould not be greater than15 m ;

the height of the building H, should not exceed twice the least width of the building W1,

the height of the wing H2 should not exceed twice the least width of the wing W 2 whenthe projection P exceeds twice the width W2.

Hnot toexceed15m

lowestground level

Maximum height

H

Minimum width

W1

H

W1 not to be less

than 0.5H

W1

H2

W2W1

P1

b. Size of extensions to domestic buildingsFor extensions, height H should not exceed the relevant limits shown below (see also 1.D.38)where H is measured from the top of the foundation or from the underside of the floor slabwhere this provides effective lateral restraint.


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Maximum roof

slope 40

domestic

building

3.0m

max

Domesticbuilding

extension

4.5m

max

==

3.0mm

ax

c. Size of single storey , single skin buildingsSmall single-storey , single skin buildings the height H of the building should not exceed 3m and W(the length or width whichever is more ) shall not exceed 9m (see also 1.D.38) where H ismeasured from the top of the foundation or from the underside of the floor slab where thisprovides effective lateral restraint

3.0mmax

3.0mm

x

Maximum roofslope 40

IIII

3.6mm

ax

1.D.3 Maximum floor areahe guidance in this annex applies where -

1. Floors enclosed by structural walls on all side do not exceed 70 m2; andd 36 m2

Ts

floors without a structural wall on one side do not excee


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Area notexceeding36 m2


Area notexceeding

36 m2


Area not

exceeding 70 m2

Area notexceeding 70 m

2

Area not

exceeding 70 m2

1.D.4 Imposed loads on roofs , floors and ceilingsThe imposed loads on roofs, floors and ceilings should not exceed those given in the table below.

Element Loading

Roof distributed load: 1.00 kN/m2 for spans up to 12 metres

1.50 kN/m2 for spans up to 6 metres

Floors distributed load: 2.00kN/m2 together with a concentratedload of 1.4 kN

Ceilings distributed load: 0.25 kN/m2 together with concentratedload: 0.9 kN

The guidance for snow loading in 1.F.6 applies only to a free standing flat roofed structure withno parapet and with the roofon one level only, provided that there are no otherbuildings within1.5m of its perimeter.


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Thickness of walls1.D.5 GeneralWall thickness should be determined according to this Annex provided the following conditionsare met-

a. relating to the building of which the wall forms a part in 1.D.2-4 and 1.D.14 (3.4 , 3.15 to 3.17);andb. relating to the wall in 1.D.15-41 (3.18 to 3.41).Wall thicknesses may be affected by adequate bearing for precast concrete units.

Conditions buildinga. limitations on size andproportions ofbuilding and parts ofbuilding ( 1.D.2 )b. max allowable floor areas (1.D.3)c. max imposed and wind loads (1.D.4 and 1.D.14)

Conditions walla. max allowable length andheight of wall ( 1.D.15)

b. construction materials andworkmanship ( 1.D.16-23)c. loading on walls ( 1.D.24-25)d. end restraints ( 1.D.26-28)e. openings , recesses ,

overhangs, chases (1.D.29-33)

f. lateral support by floors androofs (1.D.34-36)

g. movement in masonry (1.D.37)h. conditions relating to external

walls of small single storeybuildings and extensions (1.D.38-41)

Conditions relating to

building of which wall

forms part

Use 1.D.6-13 for wall

thickness assessment

Yes


wall

Yes

Are building conditions

satisfied?

Outside Annex

1.D scope

OutsideAnnex

1.D scopeN

Are wall conditions

satisfied ?


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1.D.6 Solid external walls, compartment walls and separating walls in coursed brickwork orblockwork

Solid walls constructed of coursed brickwork or blockwork should be at least as thick as 1/16 ofthe storey height. Further requirements are given in the table below.

Height ofwall Length of wall Minimum thickness ofwallnot exceeding3.5m

not exceeding 12m 190mm for the whole of its height

not exceeding 9m 190mm for the whole of its heightexceeding 3.5mbut notexceeding 9m

exceeding 9m but notexceeding 12m

290mm from the base for the height of one storey,and 190mm for the rest of its height

not exceeding 9mbut not exceeding 12m

290mm from the base for the height of one storey,and 190mm for the rest of its height

exceeding 9mbut notexceeding 12m exceeding 9m but not

exceeding 12m290mm from the base for the height of two storeys,and 190mm for the rest of its height.

1.D.7 Solid external walls, compartment walls and separating walls in uncoursed stone,flints etcThe thickness of walls constructed in uncoursed stone or bricks or other burnt or vitrified materialshould not be less than 1.33 times the thickness required by 1.D.6.

1.D.8 Cavity walls in coursed brickwork and blockworkAll cavity walls should have leaves at least 90 mm thick and structural cavities at least 50 mm wide.The wall ties should have a horizontal spacing of 900mm and a vertical spacing of 450mm, which isequivalent to 2.5 ties per square metre. Wall ties should also be provided, spaced not more than300mm apart vertically, within a distance of 225mm from the vertical edges of all openings, movementjoints and roofverges. For selection of wall ties for use in a range of cavity widths refer to Table to1.D.16. For specification of cavity wall ties refer to paragraph 1.D.16.

For external walls, compartment walls and separating walls in cavity construction, the combinedthickness of the two leaves plus 10 mm should not be less than the thickness required by 1.D.6 fora solid wall of the same height and length.

1.D.9 Walls providing vertical support to other wallsIrrespective of the materials used in the construction, a wall should not be less in thickness thanany part of the wall to which it gives vertical support.

1.D.10 Internal loadbearing walls in brickwork or blockworkWith the exception ofcompartment walls orseparating walls internal loadbearing walls should havea thickness not less than :

(specified thickness from 1.D.6) /2 less 5 mm

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 above equation or 140 mm, whichever is thegreater.


22/85


1.D.11 Parapet wallsThe minimum thickness and maximum height of parapet walls should be as given in the table anddiagrams below only where access is limited ( e.g. for occasional maintenance ).

Cavity wall

Max parapet height H(mm)

Thickness(mm)

600 t1+t2 not more than 200

860 t1+t2 more than 200

Solid wall600 t = 150

760 t = 190

860 t = 215

Note that t must not be more than T

level of junction

of wall and

structural roofT

t

Hp

t1t2

level of junctionof wall and

structural roof

1.D.12 Single leaf external walls

The single leaf of external walls of small single storeynon-domestic buildings and of extensionsneed be only 90 mm thick, provided the requirements of 1.D.38-41 are met.

1.D.13 Modular bricks and blocksWhere walls are constructed of bricks or blocks having modular dimensions derived from BS 6649 -

985 wall thicknesses recommended in this Annex which derive from a dimension of a brick orblock may be reduced by an amount not exceeding the deviation from work size permitted by aBritish Standard relating to equivalent sized bricks or blocks made of the same material.

1


23/85


1.D.14 Maximum height of buildings based on wind loadingsThe maximum height ofbuilding which should be adequate for the various site exposure conditionsand wind speed should be derived by following the procedure which is set out on the Flow Chartbelow using the map of wind speeds , topographic zone diagrams below and tables 1 and 2 enablingthe maximum height ofbuilding to be read off table 3 oppositeThis design guidance has been revised in accordance with Wind loading on Traditional dwellings andis based on BS 6399: Part 2 1997 using hourly mean wind speeds and it should be noted that thewind speeds are derived from a different basis than in the Small Buildings Guide and it is importantthat they are only applied to the methodology within this annex.

Flow chart for deriving maximum allowable building height

Lu LuLu

Lu0.25

LuLu0.4

Z2 Z1 Z2 Z3Win

di ectionr

Lu

0.25 0.4 1.2

Hills and ridges

Map of wind speeds ( m/sec)

Z2 Z1 Z2

Winddirection

0.4 Ld

0.4 Ld

Lu

0.4 Lu

0.4 Lu

Ld

Cliffs and escarpments

Topographic zones for Table 1

Read

windspeed

,V from

map above

Topographic

zone from

above

diagrams

Read

Factor ,T

from

Table 1

Factor

A from

table 2

Factor

S =

VxTxA

Max

allowable

building

height

fromTable 3


24/85


Table 1 Factor T Table 2 Factor A

Factor T Site Altitude

(m)

Factor ATopographic category and

average slope of whole

hillside, ridge, cliff orescarpment

Zone1

Zone2

Zone3

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

0

50

100

150

200

300

400

1.00

1.05

1.10

1.15

1.20

1.30

1.40

Note: Outside of these zones factor T = 1.0

Table 3 Maximum allowable building height (m)

Country Sites Town Sitesa

Distance to the coastb

Distance to the coastb

Factor

S50km 50km

23

24

2526

27

28

29

30

31

32

33

34

35

3637

38

39

40

15

15

118

6

4.5

3.5

3

15

15

14.510.5

8.5

6.5

5

4

3.5

3

15

15

1513

10

8

6

5

4

3.5

3

15

15

1515

15

13.5

11

9

8

7

6

5

4

3

15

15

1515

15

15

13

11

9.5

8.5

7.5

7

6

5.54.5

4

3

15

15

1515

15

15

14.5

12.5

10.5

9.5

8.5

8

7

65.5

5

4

3

Notesa. Forsites on the outskirts of towns not sheltered by otherbuildings use the values for country sitesb. Where a site is nearer than 1 km to an inland area of water which extends more than 1 km in the

wind direction , the distance to the coast should be taken as from the edge of the water.


25/85


1.D.15 Maximum allowable length and height of the wallThis annex does not deal with walls longer than 12 m, measured from centre to centre of buttressingwalls, piers orchimneys providing restraint, or of walls exceeding 12 m in height. (See also table to1.D.6 and 1.D.37 regarding movement joints )

Construction materials and workmanship1.D.16 Wall tiesWall ties should comply with BS EN 845-1 and be material references 1 or 3 in BS EN 845 TableA1 austenitic stainless steel or suitable non-ferrous ties. Wall ties should be selected inaccordance with the following table

Cavity wall tiesPermissible type of tieNormal cavitywidth (mm)

(Note 1)

Tie length (mm)

(Note 2)BS EN 845-1 tie (Note 4)

50 to 75 20076 to 90 22591 to 100 225( Note 3)

Types 1, 2, 3 or 4 to DD 140-2* and selected on the basisof the design loading and design cavity width

101 to 125 250126 to 150 275151 to 175 300

176 to 300 (See Note 2)

*Although DD 140-2 was withdrawn on 1 February 2005,the tie user classes (types) given in Tables 1 and 3 of thelatter document can continue to be used after this date.

Notes1 Where face insulated blocks are used the cavity width should be measured from the face of themasonry unit.2 The embedment depth of the tie should not be less than 50mm in both leaves. For cavities widerthan 180mm calculate the length as the structural cavity width plus 125mm and select the neareststock length.3 Double triangle ties having a strength to satisfy Type 2 of DD 140-2*, are manufactured. Specialisttie manufacturers should be consulted if 225mm long double triangle format ties are needed for 91 to100mm cavities.4 Reference requires to be additionally made to DD 140-2* for the selection of the type (i.e. types1, 2, 3 or 4) relevant to the performance levels given in DD140-2.

1.D.17 Brick and block constructionWalls should be properly bonded and solidly put together with mortar. Materials should be chosenfrom the following list as being suitable for their intended use and for the exposure conditions,likely to prevail -

a. clay bricks or blocks to BS 3921: 1985 or BS EN 771-1; orb. calcium silicate bricks to BS 187: 1978 or BS 6649: 1985; or BS EN 771-2 orc. concrete bricks or blocks to BS 6073: Part 1: 1981; or BS EN 771-3 or 4 ord. square dressed natural stone to the appropriate requirements described in BS 5628-3 or BSEN 771-6 ; orManufactured Stone to BS 6457: 1984 or BS EN 771-5.

1.D.18 Compressive strength of masonry unitsThe minimum compressive strength requirements for masonry units according to BS Standards andBS EN Standards are given in the Diagrams in 1.D.21 where the masonry units indicated forConditions A, B and C should have declared compressive strengths of not less than the values givenin the Table below. Normalised compressive strengths for block sized clay and calcium silicate

masonry units not complying with brick dimensional format are given in the Table to 1.D.20.


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1.D.19 Declared Compressive Strength of Masonry Units complying with BS EN 771 - 1 to 5(N/mm2)

MasonryUnit

Clay masonry unitsto BS EN 771-1

Calcium Silicatemasonry units toBS EN 771-2

AggregateConcreteMasonryUnits to BSEN 771-3

Autoclavedaerated conc.Masonry unitsto BS EN771-4

ManufacturedStone Masonryunits to BS EN771-5

Condition A

Brick Group 16.0

Group 29.0

Group 16.0

Group 29.0 6.0 -

Block See clause 1.D.20 2.9* 2.9

Condition B

Brick Group 19.0

Group 213.0

Group 19.0

Group 213.0 9.0 -

Block See clause 1.D.20 7.3* 7.3

Condition CBrick Group 1

18.0Group 2

25.0Group 1

18.0Group 2

25.0 18.0 -

Block See clause 1.D.20 7.3* 7.3 Any

unit

complying

with

BS

EN

771-5

w

ill

be

acceptable

for

condition

sA,BandC

Notes1. 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 compressivestrengths (N/mm2) are mean values.3. Brick: a masonry unit having work sizes not more than 337.5 mm in length or 112.5 mm inheight.

4. Block: a masonry unit exceeding either of the limiting work sizes of a brick and with a minimumheight of 190mm. For blocks with smaller heights, excluding cuts or make up units, the strengthrequirements are as for brick except for solid external walls where the blocks should have acompressive strength at least equal to that shown for block for an innerleaf of a cavity wall in thesame position.5. Group 1 masonry units have not more than 25% formed voids (20% for frogged bricks). Group 2masonry units have formed voids greater than 25%, but not more than 55%6. Refer to 1.D.21 for locations of Conditions A, B and C7. Values marked * are dry strengths to BS EN 772-1

1.D.20 Normalised compressive strength of masonry units of clay and calcium silicate blockscomplying with BS EN 771 - 1 and 2 (N/mm2)

Standard Condition Group 1 masonry units Group 2 masonry units

A 5.0 8.0

B 7.5 11.0

Clay masonry units toBS EN 771-1 Calciumsilicate masonry unitsto BS EN 771-2 C 15.0 21.0

Notes:1 Values in this Table are normalised compressive strengths (N/mm2). Compressive strengths ofmasonry units should be derived according to EN 772-1.2 The Table applies to clay and calcium silicate block masonry units where the work size is morethan 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 2masonry units have formed voids greater than 25%, but not more than 55%.


27/85


1.D.21 Compressive strengths of masonry units in walls

Top of

structural floor

underside

of

structural

roof

HS

WhereH Less than or equal to

Condition A1m-

f

Where

H greater than Condition B1m-f

Underside

of

structural

roof

Undersideof

structural

floor

Cavity

wall

Internal

wall

Top of

structural

floor

Hf

S

S

This wall to be at least

140 mm thick in blockwork or

215 mm thick in brickwork belowgroundfloor level if

height H exceeds 1m.f

Underside

of structural

floor

Topside ofstructural

floor

Underside

of

structuralroof

Cavity

wall

This wall to

be at least

140mm thick

blockwork or

215mm thick

brickwork

Internal

wallHS

HS

HS

Notes

f H1. I .7 m , the compressive strength of bricks or blocks should be used in walls as

2.I ed in the wall should be at

3.I pressive strength of at

o determinestrength of the masonry units where the roofconstructionis of timber.

indicated by the key

f H is more than 2.7m, the compressive strength of bricks or blocks us

S is not more than 2

S

least Condition B, or as indicated by the key whichever is the greater.

f the external wallis solid constructionthe masonry units should have a com

least that shown for the internal leaf of a cavity wall in the same position.

The guidance in the diagram for walls of two or three storeybuildingsshould only be used tthe compressive


28/85


1.D.22 MortarMortar should be -a. Mortar designation (iii) according to BS 5628:Part 3:2001;

c. 1:1: 5 or 6 CEM 1, lime and fine aggregate measured by volume of dry materials

with masonry cavity wall construction should bested by a notified body or justified by calculations

l is 6 m, where the span is measured centrecentre of bearing as shown on the diagrams below.

Wall joist hanger

b. Strength class M4 according to BS EN 998 - 2 ;

1.D.23 Lintels for openingsProprietary steel or concrete lintels suitable for useteLoading on walls1.D.24 Maximum span of floorsThe maximum span for any floor supported by a walto

Floor member bearing on Floor member bearing on

floor

floor spanmaximum 6m

centre line

of bearing

floor

wall

floor span

maximum 6m

centre line

of bearing

Loading on walls1.D.25 Other loading conditionsa. 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 annex 1.F, and wherebearing length for lintels is 150 mm or greater. Where a lintel has a clear span of 1200 mm or less

the

the wall and the combined dead and imposed

c. Walls should not be subject to lateral load other than from wind, and that covered by 1.D.25 b

the bearing length may be reduced to 100 mm. Where lintels carry a concrete floor the bearinglength should be at least 150mm or L/10 whichever is the greater, where L is the span of the lintel.b. Differences in level of ground or other solid construction between one side of the wall and theother should be less than four times the thickness ofload should not exceed 70kN/m at base of wall as shown below provided there is a full storey

height of masonry above the upper retained level.


29/85


a. Examples of ground level differences

GroundSupportedfloor slab

Retainedheight

W

Suspended

ground floor

Retained

height

W

Void

t2t1

H should be lessthan or equal to1m and less than

or equal to

4( + )t1 t2

W W

Suspended

ground floor

Retained

height

To be level for

a distance of not

less than 1.25H

mum differe lb. Maxi nces in ground leve

H

W

Retainedheight

W

Retained

heightH

t

H should be lessthan or equal to 1m

and less than

or equal to 4t

Concrete fillto wall cavity

t H should be less

and less than or

otes ed for clarity and may be on either side of the walls shown.

ull storeyheight of masonry above

nt to wallst single leaf walls less than 2.5 m in height and length in small single

torey non-domestic buildings and extensions should be bonded or otherwise securely tiedthroughout their full height to a buttressing wall, pier or chimney. Long walls may be provided withintermediate support dividing the wall into distinct lengths; each distinct length is a supported wall for

the purposes of this part. The buttressing wall, pier orchimney should provide support from the baseto the full height of the wall.

than or equal to 1m

equal to 4t

NFloor slabs in diagrams b have been omitt

Cavity walls should be tied in accordance with Table to clause 1.D.16.

These recommendations apply only to circumstances where there is a f

the upper retained level.

End restraint1.D.26 Vertical lateral restraiThe ends of every wall, exceps


30/85


1.D.27 Criteria for buttressing wallsdiagram below gives certain rules for bu

itself a supported wall, its thickness TThe ionally i f the buttressing wall isnot ld ot be less than -a. separating wall of similar height and

d does not exceed 6 m in total height and 10 m in

c.

Not

1. nded or

. The length, L , of the buttressing wall

3.

d not impair the lateral support to

. Openings or recesses in the buttressing

st

Openings in a buttressed wall

ttressing walls. Addit

2 shouhalf the thickness required by this part for an external or

n

length, less 5 mm; orb. 75 mm if the wall forms part of a dwelling an

length; or90 mm in any other case.

es

The buttressing wall should be bo

securely tied to the supported wall and

at the other end to a buttressing wall,

pier or chimney.

2 Bshould be at least 1/6 of the overall

height, H, of the supported wall.

The position and shape of the openings

shoul

be given by the buttressing wall.

T2

550mm

Supported

wall

H

4

wall more than 0.1 m2 should be at lea

550mm from the supported wall.

LB

Buttressing

5. ot more than 0.1 m2 at any position.

6. should be not more than 0.9 times the floor to ceiling

g any masonry over the opening should be not less than 150

asuring the height of the supported wall.

1.Dpro1.

ys twice the thickness,

2. The sectional area on plan ofchimneys(excluding openings for fireplaces andflues) should be not less than the arearequired for a pier in the same wall, and

required thickness of the

of the wall from base to top of wall.

Wall

There may be only one opening or recess n

The opening height in a buttressed wall

height and the depth of lintel includinmm.

Refer to diagram to 1.A.5 for the rules for me

.28 Criteria for piers and chimneyviding restraintPiers should measure at least threetimes the thickness of the supportedwall, and chimnemeasured at right angles to the wall.Piers must have a minimum width of190 mm as shown opposite.

the overall thickness should not be lessthan twice thesupported wall

3. The buttressing wall, pier orchimneyshould provide support to the full height

min190mm

H

T

centre line ofbuttressing wall

centre lineof chimney

centre lineof pier

centre line ofpier(alternativearrangement)

Buttressingwall Pier

Chimney


31/85


Openings , recesses , chases and overhangs

The number, size and position of openings and r sses should not impair the stability of a wall orthe lateral support afforded by a buttressing wall to a supported wall. Construction over openingsand recesses should be adequately supported.

gs and reram and t

grouu a

1.D.29 Generalece

1.D.30 Dimensional criteria for openin cesses

able below.The dimensional criteria are given in the diags belowNo openings should be provide in wall

n lnd floor except for small holes for services andm rea of 0.1 mve ti ation etc. which should be limited to a maxim

2 at not less than 2 m centres .

1.D.31 Sizes of openings and recesses

Opening

W1

Opening

W2

Recess

W3P4P3P2P1

Opening

W4

H

outer fa of

return w

corner of twoexternal walls

ce

all

P5

should n exceed 2L/3. None of W1 or W2 or W3 should exceed 3m

e greater than W1/X

reater than or equal to W1/X

7. P5 should be gre r th or eq l to Wbut should not be less than 665 mm.

8. The value of Factor X should be taken fromthe table below or can be given the value 6,

th of the

the case of a cavity wall,

.

wall into wall

Max Max Max Max

Notes

1. W1 + W2 + W3 ot2

3. P1 should not b

4. P2 should not be g

5. P3 should be greater than or equal to (W2+ provided the compressive strengW3)/X bricks or blocks (in

6. P4 should be greater than or equal to W3/X in the loaded leaf) is not less than 7 N/mm

ate an ua 4/X

2

Value of factor 'X' (see diagram above)

Nature ofro Span oftimber floor

into

Span ofconcrete floor

ofspan

Maximum roofspan (m)

Minimumthickness ofwall inner

Span of flooris parallel towall

(mm)

4.5m 6.0m 4.5m 6.0m

Value of factor 'X'

100 6 6 6roof spans 6 6

parallel to wallnon applicable

90 6 6 6 6 5

100 6 6 5 4 3timber roof9

spans into 6 3wall 90 4 4 3


32/85


1.D.32 ChasesChases should not -

an 1/3 of wall thic ess or, in cavhan 1/6 of the thickness of the leaf or wall; and

mpair the stability of the wall, pa d.

1.D.33 Overhangsang, the amount of any projection should not impair the stability

the inte een diffempair the st all.

in clauses 1.D.34-35 .The requirements for lateral support of walls at roofand floor levels are given in the table below andguidance on satisfying the requirements is given in clauses 1.D35 and 1.D.36

Wall Type Wall Length Lateral support required

any length rooflateral support by every roofforminga junction with the supported wall

a. if vertical, be deeper thb. if horizontal, be deeper t

kn ity walls, 1/3 of leaf thickness ;

c. be so positioned as to i rticularly where hollow blocks are use

In constructing a corbelled overhof the wall.Minor overhangs may occur atdifferences in thickness provided this does not i

rfaces betw rent masonry materials which have minorability of the w

1.D.34 Lateral support by roofs and floorsThe walls in each storey of a building should extend to the full height of that storey, and havehorizontal lateral supports to restrict movement of the wall at right angles to its plane.Floors and roofs should -a. act to transfer lateral forces from walls to buttressing walls, piers orchimneys; and

b. be secured to the supported wall by connections specified

Solid or cavity: external

compartment separatinggreater than 3 m

floor lateral support by every floorforming a junction with the supportedwall

internal load-bearing wall

(not being a compartment orseparating wall)

any lengthroofor floor lateral support at the top ofeach storey

Walls should be strapped to floors above ground level, at intervals not more than 2 m by tensiontraps as shown below to BS EN 845-1. For corrosion resistance purposes , the tension straps

16.1 or 16.2 (galv nised steel) or other more resistantc stainless steel). The declared tensile

sshould be material reference 14 or aspecifications including material references 1 or 3 (austenitstrength of tensions straps should not be less than 8 kN

i


33/85


30 x 5mm galvanised mild

p

onry

3 joists

Dwangs minimum 38mm

width to extend

at least depth of joist

steel or other durable stra

held tight against mas

wall and fixed across

30x5mm galvanised mild

steel or other durable strap

at least 1200mm long and

held tight against masonry

wall

internal leaf of external cavity

wall requiring lateral restraint

Tension strap detail 1 Tension strap detail 2

Tension straps need not be provided -

a. in the longitudinal direction of joists in domesticbuildings of not more than two storeys, if the joists areat not more than 1.2 m centres and have at least 90mm bearing on the supported walls or 75mm bearingon a timber wall- plate at each end ,and

b. in the longitudinal direction of joists in domesticbuildings of not more than two storeys, if the joistsare carried on the supported wall by joist hangers inaccordance with BS EN 845-1 of the restraint typedescribed in BS 5628:Part 1 and shown opposite andare incorporated at not more than 2 m centres;

c. where a concrete floor has at least 90 mm bearing onthe supported wall as opposite;

d. where floors are at or about the same level oneach side of a supported wall and contact

between the floors and wall is either continuousor at intervals not exceeding 2m. Where contact

is intermittent, the points of contact should be inline or nearly in line on plan as shown on thediagrams below.

Restraint type joist hanger

X

X to be not less than 90mm

X

Restraint by concrete floor orroof


34/85

domestic structure SBSG annex 1.E 2007

Restraint of internal walls

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

y tension straps as shown in the diagrams

ating 2m if the roof-

by local experience to be

d. o thesupported wall at not more than 1.2 m centr s. um

ofthi

ckness

s+10

mm

Tension

1.D.35 Gable wall strapping

Gable walls should be strapped to roofs as shown

opposite bopposite .

Vertical strapping at least 1m long should be providedeaves level at intervals not exceeda. has got a pitch of 150 or less;b. is not tiled or slated;c. is not of a type knownresistant to wind gusts; and

has not got main timber members spanning ont

straps

st point If H is greater

Tension straps

at not more than

2 metre centres

Gableend

wall

t

at highe

that will provide a

secure connection

than 16t, provide

restraint hereat not greater

than 2m centres

e=sof

leave

h

X X/2

X/2

Tension strap location

Effective strapping at gable Vertical strapping at eaves Vertical strapping at eaves

dwang

packStrap turnedover uncutblock

Rafter fixed towall plate with

framing anchoror truss clip

strap anchoredto wall and rafter

Each joist fixed to wall-plateWith framing anchors

Or skew nails

Strap anchored towall and turnedover wall plate


35/85


1.D.36 Interruption of lateral supportWhere a stair or other opening in a floor or roofadjoins a supported wall and interrupts the continuityof lateral support-a. the length of the opening should be not more than 3 m, measured parallel to the supported wall;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;c. where connection is provided by anchors, these should be spaced closer than 2 m on each side

of the opening to provide the same number of anchors as if there were no opening; andd. there should be no other interruption of lateral support.

1.D.37 Movement in masonryMax spacing of movement jointsClay brickwork 12 m centresCalcium silicate brickwork 7.5 m centresConcrete brickwork and blockwork 6 m centres

Reference should be made to BS 8103-2, Annex B Code of practice for masonry walls for housingwhich provides general guidance for movement joints.


36/85


External walls of small single storey single skin buildings and extensions1.D.38 GeneralThe guidance given applies in the following circumstances:-

a. The floor area of the building or extension does not exceed 36m2

b. The walls are solidly constructed in brickwork or blockwork using materials which comply withclauses 1.D.16-1.D.23.

c. Where the floor area of the building or extension 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

orless.)d. Access to the roofis only for the purposes of maintenance and repair.e. The only lateral loads are wind loads.f. The maximum length or width of the building or extension does not exceed 9m.g. The height of the building or extension does not exceed the lower value derived from the Diagramsto clause 1.D.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 roofstructure vertically and horizontally in accordance with clauses 1.D.34-36and with horizontal lateral restraint at rooflevel in accordance with clause 1.D.41.j. The roofstructure of an extension is secured to the structure of the main building at both rafter andeaves level.

1.D.39 Size and proportions of openingsOne or two major openings not more than 2.1m in height are permitted in one wall of the building orextension only. The width of a single opening or the combined width of two openings should notexceed 5m.The only other openings permitted in a building or extension are for windows and a single leaf door.The size and location of these openings should be in accordance with the diagram below.

Notes1. Major openings should be restricted to

one wall only. Their aggregate width

should be not more than 5.0m and their

height should not be more 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 be

not more than 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 les s than 390 mm.

Isolated column

Nootheropeningsinthiszone

2.0m

Wall with major

openings

390mm

min

390mm min


37/85


1.D.40 Wall thicknesses and piersThe walls should have a minimum thickness of 90mm.The minimum pier size ( AP x BP) should be 390mm x 190mm or 327mm x 215mm depending on the

olated columns should 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 ortied to piers for their full height at not more than 3m centres as shown in the diagram belowWall without a major opening

m max 3.0m max

size of the masonry unitsIs

3.0m max 3.0

90mm minBPAP AP

ould beat, 20mm x 3mm in cross section, be in

stainless steel in accordance with clause1.D.16, be placed in pairs and be spaced atnot more than 300mm centre vertically

Wall with a single major openingWalls which contain one or two major openingsshould in addition have piers as shown in theDiagrams above and opposite. Where ties areused to connect piers to walls they shfl G

BP

AP

Dotted line

indicates range

of wall positions

G > 2.5mAP

BP

BP

AP

G 2.5m

Wall with two major openingsDotted line indicates

range of wall positions

AP

BP

CC

CC


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1.D.41 Horizontal lateral restraint at rooflevelWalls should be tied horizontally at no more than 2m centresto the roofstructure at eaves level, base of gables and alongroof slopes with straps fixed in accordance with clauses

ass through a1.D.34 and 1D.35 and where straps cannot pwall they should be adequately secured to the masonry usingsuitable fixings and isolated columns should also be tied tothe roof structure all as shown below. Fixings should be inaccordance with the diagram opposite.

1.D.42 Proportions for Masonry ChimneysWhere a chimney is not adequately supported by ties or securely restrained in any way, its height if

easured from the high st point of intersection with the roofsurface, gutter, etc should not exceed.5W, provided the density of the masonry is greater than 1500 kg/m3 where -

W is the least horizontal dimension of the chimney measured at the same point of intersection; andH is measured to the top of any chimney pot or other flue terminal.

em4

H H

W W

Level of highestpoint of

intersection


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domestic structure SBSG annex 1.F 2007

Annex1.E Timber frame walls1.E.0 Introduction1.E.1 Wall types1.E.2 Conditions relating to the Building of which the walls forms part

1.E.3 Maximum floor area1.E.4 Imposed loads on roofs , floors and ceilings

Wall structure1.E.5 General1.E.6 Minimum thickness ofexternal walls1.E.7 Walls providing vertical support to other walls1.E.8 Timber frame wall sizing1.E.9 Site data1.E.10 Building data1.E.11 Horizontal loads1.E.12 Wall sheathing1.E.13 Site data and building data

1.E.14 Altitude/distance category1.E.15 Length/width ratio1.E.16 Racking bands1.E.17 Percentage openings1.E.18 Masonry cladding arrangements1.E.19 Panel sheathing and nailing1.E.20 Vertical loads1.E.21 Wall stud sizing1.E.22 Cripple stud sizing1.E.23 Lintel sizing1.E.24 Example1.E.25 Overall stability

1.E.26 Maximum allowable length and height of wallConstruction materials and workmanship

1.E.27 General1.E.28 Wall ties1.E.29 Masonry cladding1.E.30 Brick and block construction1.E.31 Mortar1.E.32 Lintels for masonry cladding1.E.33 Timber members1.E.34 Wall sheathing1.E.35 Fasteners

1.E.36 Fabrication1.E.37 Composite action1.E.38 Wall panel connections1.E.39 Nailing and fixing schedule

Loading on walls1.E.40 Maximum span of floors1.E.41 Other loading conditions1.E.42 End restraint

Openings, notching and drilling1.E.43 General1.E.44 Framing of openings1.E.45 Dimensional criteria for openings

1.E.46 Small unframed openings1.E.47 Notching and drilling1.E.48 Lateral support by roofs and floors1.E.49 Differential movement


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annex

1.EWalls in certain small buildings timber frame

1.E.0 Introduction

Small buildings of masonry clad platform frame construction can be designed to provide designstaking into account loading conditions , limitations on dimensions , openings and subject to , restraintconditions .This structural guidance for timber frame construction for small buildings is intended to be similar tothat for masonry construction restricted to cover a limited range of timber frame wall dimensions,member sizes and loading conditions which commonly apply in Scotland.To comply with the philosophy of the Small Buildings Structural Guidance, the guidance for timberframe construction has been produced for use by those who have expertise in building design andconstruction but not necessarily in structural engineering design. Where the conditions or parametersfall outside the scope then specialist advice should be sought from chartered engineers with theappropriate skills and experience.This guidance is based on the Platform Frame method of timber frame construction with external

masonry cladding being the most common form of timber frame construction in Scotland It isrestricted to the member sizes and types and sheathing materials which are commonly used in smallbuildings in Scotland.It should be noted that the guidance within this Annex only relates to Section 1 Structure. There areother factors such as cavity barriers, breather membranes ,thermal insulation, etc which may berelevant and reference should be made to the appropriate sections in the Technical Handbooks.Timber frame construction outwith the parameters and materials covered in this guidance should bedesigned in accordance with the guidance in BS 5268 Part 6.1 1996.

This Annex provides guidance for timber frame wall construction for the following building typesa. domestic buildings of not more than 2 storeys where loading criteria for individual floors does not

exceed those given in 1.E.4 and total limit of loading does not exceed that given in 1.E.41;

There is guidance in Annex 1.D: Masonry walls which is relevant to this annex with respect tomasonry cladding to timber frame walls.

1.E.1 Wall typesThis Annex deals only with the types of wall extending to full storey height set out below.a. Domestic buildings of not more than 2 storeys

External walls


Compartment walls

Separating walls

This Annex should be used in conjunction with Annexe 1.B ; and

a. if a timber wall structure is designed in accordance with the guidance in Annex 1.E, allappropriate design conditions should be satisfied;b. walls should comply with the relevant recommendations of BS 5268: Part 6.1: 1996, except as

regards the conditions given in 1.E.2,1.E.3-4 and 1.E.8-49c. in formulating the guidance of this Annex, the worst combination of circumstances likely to

arise was taken into account.d. If a recommendation of this Annex is considered too onerous in a particular case then

adequacy by calculation should be shown in respect of the aspect of the wall which issubject to the departure rather than for the entire wall;

e. the guidance given in this Annex is based upon the material strengths of timber , sheathing ,plasterboard and masonry being not less than that indicated in 1.E.27-39

f. roofconstruction should be :

duo or mono pitch trussed rafters with 15-45o

pitch and dead weight not more than 1.036kN/m2 on the slope


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orflat ,raised tie or collared roofs in accordance with guidance in Annex 1.F.g. floordead load should be not more than 0.5 kN/m2h. Internal , party and external wall dead loads should be not more than 1.5 kN/m excluding

masonry claddingi. panel heights should be not more than 2.7 mj. timber frame walls act should compositely with the masonry cladding ,sheathing and inner

plasterboard lining all contributing to the racking resistance of the timber frame walls.This guidance does not cover hipped ends to roofs with girder trusses which impose point loads on tothe walls or other situations where point loads occur.Wall sheathing which provides the racking resistance to wind loading generally is the limiting factorand this aspect should be checked prior to carrying the remainder of the design. It is unlikely that thisguidance could be used with walls with openings more than 30 % of the total wall area or for frontgable buildings where there are large percentage openings in the shorter length walls.

1.E.2 Conditions relating to the Building of which the walls forms partThis Annex applies only to buildings having proportions within the following limits and as shownon the Diagrams below subject to the limits of 1.E.26

The maximum height of the building measured from the lowest finished ground level adjoiningthe building to the highest point of any wall orroofmust not be greater than:

10 m for duo pitch roofs 5.5 m for mono pitch orflat roofs

the height of the building H, should not exceed twice the least width of the building W1,the height of the wing H2 should not exceed twice the least width of the wing W 2 when theprojection P exceeds twice the width W2.

lowest

ground level

Maximum height

Hnot to

exceed

10m

H

Minimum width

W1

H

W1 not to be less

than 0.5H

W1

H2

W2W1

P1

1.E.3 Maximum floor areaThe guidance in this annex applies where -

Floors enclosed by structural walls on all sides do not exceed 70 m

2

; and floors without a structural wall on one side do not exceed 36 m 2


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Area notexceeding 70 m2



Area notexceeding36 m 2




The i on roofs ceilings should not exceed those given in the table below.

Roof distributed load:

1.50 kN/m for spans up to 6 metres

1.E.4 Imposed loads on roofs , floors and ceilingsmposed loads

Element Load

, floors and

ing

1.00 kN/m for spans up to 12 metres

2

2

Floors distributed load: kN/m together with a concentrated load of 1.42.00 2

kN

Ceilings distributed load: 0.25 kN/m together with concentrated load: 0.9 kN2

The guidance for snow loading in 1.F.6 applies only to a free standing flat roofed structure with noparapet and with the roofon one level only, provided that there are no otherbuildings within 1.5mof its perimeter.


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Wall structure1.E.5 GeneralWall structure should be determined according to this Annex provided the following conditions aremet-

a. relating to the building of which the wall forms a part (1.E.2); andb. relating to the wall 1.E.3-49

Conditions buildingd. limitations on size and proportions ofbuilding and parts ofbuilding ( 1.E.2, )e. max allowable floor areas ( 1.E.3)f. max imposed and wind loads (1.E.12.)

Conditions walli. max allowable length and height ofwall ( 1.E.26)j. construction materials andworkmanship ( 1.E.27-39)k. loading on walls ( 1.E.40 and 1.E.41)l. end restraints ( 1.E.42)m. openings, notching and drilling(1.E.43-47)n. lateral support by floors and roofs(1.E.48)o. Differential movement (1.E.49)

Are building

conditions satisfied ?

Use Annex 1.E for

timber frame walls


building of which wall

is part

Outside

Annex 1.E

scope

Outside

Annex 1.E

scope

Yes

Are wall conditions

satisfied?

No

No

Yes

1.E.6 Minimum thicknesses of external cavity walls

Masonry clad timber frame walls should comprise masonry cladding for at least 100 mm thick ,50 mmnominal cavity width 9mm nominal sheathing thickness and timber studs at least 89 mm depth andplasterboard innerwall lining . Wall ties should be securely nailed to the vertical studs and not to thesheathing alone generally at the following spacingsa. Brickwork cladding: horizontal spacing of 600mm and a vertical spacing of 375mmb. Blockwork cladding : horizontal spacing of 400 or 600mm and a vertical spacing of 450mm,c. Wall ties should also be provided, spaced not more than 300mm apart vertically, within a distanceof 225 mm from the vertical edges of all openings, movement joints and roofverges.d. In exposed wind locations, the tie density would require to be increased in accordance with BS5268 -6.1:1996.e. For specification of cavity wall ties refer to 1.E.28

1.E. 7 Walls providing vertical support to other wallsIrrespective of the materials used in the construction, a wall should not be less in thickness thanany part of the wall to which it gives vertical support.


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1.E.8 Timber frame wall sizingThe following procedure which should be followed to determine the member sizing etc for masonryclad timber frame wall construction which should be adequate for a particular location depending onthe building dimensions and the site exposure conditions is based on BS 5268-6.1The procedure is summarised in the flow chart below and explained in detail thereafter together with aworked example in 1.E.24.

Design Procedure Flow Chart

Assess Building Data( 1.E.10)

Length / Width ratio (1.E.11

Assess Site Data( 1.E.12)

Wall Sheathing Requirements(1.E.13-18)

Horizontal(Wind) Loads (1.E.19)

Vertical(Snow ) Loads ( 1.E20)

Wall Stud Requirements ( 1.E.21)

Cripple Stud Requirements(1.E.22)

Lintel requirements (1.E.23)


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1.E.9 Wall sheathingThe horizontal loads arising from wind action are resisted and transferred to the base of the walls bythe racking resistance of the racking ( or wind) wall panels .Walls should only be considered to be Racking Walls and hence able to provide resistance to windaction if they are specifically designed in accordance with the following racking procedure and have atleast one layer of OSB3 or plywood sheathing secured to the timber studs.The Flow Chart below and subsequent clauses provide guidance on how to provide adequate rackingresistance by means of racking or wind walls comprising wall sheathing and nailing arrangements ..

Racking Procedure Flow Chart

Building and Site Data including assessing = B/A (1.E.10-12)

Read off Altitude-Distance Category from Table to 1.E.13

Assess the percentage openings in each wall of Building(1.E.15)

Assess the Masonry Cladding Arrangement from Table to 1.E.16

Select Panel Sheathing and Nailing requirements (1.E.17)

Read Racking Band from Tables to 1.E.14

Use of internal racking walls, if appropriate (1.E.17)


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1.E.10 Building Data stage 1Assess the following dimensions for thebuilding :

Overall outside plan width , A Overall outside plan length, B

Height from ground level to eaves ,H

Overall Building Height from groundlevel to ridge

Number ofstoreys

Roof shape :- duopitch , monopitch orflat

Spans ofroofand floors

Key

A : BuildingWidth (smaller dimension of

the buildingcross-section (plan)B : BuildingLength (larger dimension of the

buildingcross-section (plan)

: Length/ Width Ratio of the building

plan

= B/A.

Building dimensions

H

Duo pitch roof Mono pitch roof

AR

BR

A

B

Flat roof Plan

1.E.11 Length/width ratio stage 2Determine the length/ width ratio, in accordance with the diagram aboveNote that should always be rounded up from the derived value to the nearest 0.5 and will be notless than 1.0 in any case.


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1.E.12 Site Data stage 3a. Determine the site location of the building under considerationb. Assess the distance of the site to the coast within the following ranges

Not more than 10 km

not more than 100 km greater than 100 kmWhere a site is nearer than 1 km to an inland area of water which extends more than 1 km in thewind direction , the distance to the coast should be taken as from the edge of the water.

c. Assess the altitude of the site above ordinance datum within the following ranges

0 m

not more than 50 m

not more than 100m

not more than 150m

not more than 200m

not more than 300m

not more than 400 m

d. Determine the snow zone as A or B from the snow map belowDetermine the wind speed from the wind speed map below

Snow Zone Map Wind Speed Map ( m/s)

Inverness

Zone

A

B


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1.E.13 Altitude/distance category stage 4the Site Altitude and Distance to the coast,

AD1-AD6 :Altitude / Distance to the coastCategory< : less than

Usingread the Altitude-Distance category (AD1-AD6) fromthe table opposite

Key

< : not more than

le Alti istan tegnce t coa )

Tab tude/d ce ca oryDista o the st(km

Altitude


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Ra ng s focki Band r Duopitch roofsTa 2

. ig 0 e

ble Wind speed = 27m/s

5 5 He ht 1 m H ight

Al e ta C go A Al e ta go titud /Dis nce ate ry ( D) titud /Dis nce Cate ry (AD) Side

D1 AD2 AD3 AD4 D5 AD6 AD7 D1 AD2 AD3 AD4 D5 AD6 AD7

1 A R2 R2 R3 R3 3 R4 R4 4 R5 R6 7R 9 R11 -B R2 R2 R2 R3 3 R3 R4 6 8R6 R7 R 9 R11 -

1.5 A R5 R5 R6 R6 7 R8 R9 11 1R1 - - - -B R1 R2 R2 R2 2 R2 R3 4 R5 - - - -

2 A R7 R7 R8 R9 11 1 1R1 R1 - - - - -B R1 R1 R1 R1 2 R2 R2 - - - - -

2.5 A R8 R9 R11 R11 11 - - - - - - -B R1 R1 R1 R1 1 - - - - - - -

3 A R9 R11 1R11 R1 - - - - - - -B R1 R1 R1 R1 - - - - - - -

3.5 1A R11 R11 R1 - - - - - - - -B R1 R1 R1 - - - - - - - -

4 A R11 R11 - - - - - - - - -B R1 R1 - - - - - - - - -

Racki ang B nds for Duopitch roofs

Table 3 Wind speed = 25m/sHe t m H ght5.5 igh 10 ei

Altitud is e go A u is e g Ae/D tanc Cate ry ( D) Altit de/D tanc Cate ory ( D)

Side

AD1

AD2

AD3

AD4

AD5

AD6

AD7

AD1

AD2

AD3

AD4

AD5

AD6

AD7

1 A R2 R2 R2 R2 R3 R3 R3 R4 R4 R5 R6 11R7 R9 RB R2 R2 R2 R2 R3 R3 R3 R5 R5 R6 R7 R7 R8 R9

1 1 1 1.5 A R4 R4 R5 R5 R6 R7 R7 R1 R1 R1 - - - -B R1 R1 R1 R2 R2 R2 R2 R3 R4 R4 - - - -

2 A R5 R6 R7 R7 R8 R9 R11 - - - - - - -B R1 R1 R1 R1 R1 R1 R2 - - - - - - -

2.5 1A R7 R7 R8 R9 R11 R11 R1 - - - - - - -B R1 R1 R1 R1 R1 R1 R1 - - - - - - -

3 A R8 R8 R9 R11 R11 R11 - - - - - - - -B R1 R1 R1 R1 R1 R1 - - - - - - - -

3.5 1A R8 R9 R11 R11 R1 - - - - - - - - -B 1 1 1 1 1R R R R R - - - - - - - - -

4 A R9 R11 R11 R11 - - - - - - - - - -B R1 R1 R1 R1 - - - - - - - - - -


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R ki Baac ng nds for Duopitch roofs

Table 4 Wind speed = 23m/s

5.5 H t Heigh 10m eight

Altitu Dis e eg A itu i ce g (de/ tanc Cat ory ( D) Alt de/D stan Cate ory AD)

Side AD1 D2 AD3 AD4 AD5 AD6 AD7 AD1 AD2 AD3 AD4 AD5 D6 AD7

1 A R1 R2 R2 R2 R2 R2 R3 R3 R3 R4 R5 R6 7 R9B R1 R1 R2 R2 R2 R2 R2 R4 R4 R5 5R R6 7 R8

1.5 11 1A R3 R3 R4 R4 R5 R5 R6 R8 R9 R9 R R1 -B R1 R1 R1 R1 R1 R2 R2 R3 4R3 R3 R R4 -

2 A R4 R5 R5 R6 R7 R7 R8 R11 1R1 - - - -B R1 R1 R1 R1 R1 R1 R1 R2 R2 - - - -

2.5 A R5 R6 R6 R7 R8 R9 R11 - - - - - -B R1 R1 R1 R1 R1 R1 R1 - - - - - -

3 A R6 R7 R7 R8 R9 R11 R11 - - - - - -B R1 R1 R1 R1 R1 R1 R1 - - - - - -

3.5 1 -A R7 R7 R8 R9 R11 R11 R1 - - - - -B R1 R1 R1 R1 R1 R1 R1 - - - - - -

4 A R7 R8 R9 R11 R11 R11 - - - - - - -B R1 R1 R1 R1 R1 R1 - - -- - - - -

R king Baac nds for Monopitch roofs

T 3 e eable 5 Wind speed = 0m/s Tabl 6 Wind spe d = 27m/s

Height He 5.5 5.5 ightAltitu Dis e eg A itu i ce g (Ade/ tanc Cat ory ( D) Alt de/D stan Cate ory D)

Side AD1 AD2 AD3AD4 5 6 7 4 6AD AD AD AD1 AD2 AD3 AD AD5 AD AD71 A R5 R6 R6 R7 8R8 R R9 R4 R5 R5 R6 R6 R7 R8

B R3 3 4 3R3 R R4 R4 R R5 R2 R2 R3 R R3 R3 R4

1.5 1 1 11 1A R1 R1 R - - - - R8 R9 R9 R R1 - -

B R2 2 1 2R2 R - - - - R R2 R2 R R2 - -2 A - - - - - - - R11 1R1 - - - - -B - - - - - - - R1 R1 - - - - -

2.5 A - - - - - - - - - - - - - -B - - - - -- - - - - - - - -

R ing Baack nds for Monopitch roofs

Table 7 Wind speed = 25m/s Table 8 Wind speed = 23m/s

e5.5 Height 5.5 H ightAltitu Dis e eg A itu i ce g (de/ tanc Cat ory ( D) Alt de/D stan Cate ory AD=

(B / SideA) AD1 D2 AD3 AD4 AD5 AD6 AD7 AD1 AD2 AD3 AD4 AD5 D6 7AD

1 A R3 R4 R4 R5 R5 R6 R6 R3 R3 R3 R4 R4 5 R5B R2 R2 R2 R2 R3 3R R3 R1 R1 R2 R2 R2 2 R3

1.5 - 11 1A R7 R7 R8 R9 R1 R R1 R5 R6 R6 R7 R8 9 RB R1 R1 R1 2R2 R2 R R2 R1 R1 R1 R1 R1 2 R2

2 A R9 R11 11 1 1R R1 - - - R7 R8 R9 R R1 11 -B R1 R1 1R R1 - - - R1 R1 R1 R1 R1 1 -

2 1 1.5 A R11 R1 - - - - - R9 R9 R R1 - -B R1 R1 - - - - - R1 R1 R1 R1 - -

3 A R11 - 1- - - - - - R11 R11 R1 - - -B R1 -- - - - - R1 R1 R1 - - -

3 - - R 1.5 A - - - - - 11 R1 - - - -

B - - - - - - - R1 R1 - - - -4 A - - - - - - - R11 - - - - -B - -- - - - - R1 - - - - -


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Rack g Bain nds for Flat roofs

Table 9 Wind speed = 30m/s Table 10 Wind speed = 27m/s

Height H t5.5 5.5 eightu is e g (A itu i ce eg (AAlti de/D tanc Cate ory D) Alt de/D stan Cat ory D)

Side 6 7AD1 AD2 AD3 AD4 AD5 AD AD AD1 AD2 AD3 AD4 AD5 AD6 AD71 A R4 R5 R5 R6 R6 R7 R7 R4

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