Bricklayers Pocket Book

7/29/2019 Bricklayers Pocket Book

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Guarantee range o structural warranties. MD Insurance Services Ltd is

authorised and regulated by the Financial Services Authority.

Bricklayers Handbook

Superstructures

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Introduction

The Bricklayers handbook gives guidance to site managers and

site sta on key issues aced during construction or traditional

masonry construction. For other types o construction, pleasereer to alternative guidance, British Standards or specialist

design inormation.

Geographical location can vary the design signicantly and

although this guide gives examples o the most commonly

occurring issues, Premier Guarantee recommend early contact

with our surveyors to help give guidance on how to avoid

particular circumstances on your site.

Please reer to the Premier Guarantee Technical Manual or the

Functional Requirements, Principal Perormance Standards /

Requirements or the design and construction o Housing units

using Premier Guarantee.

Please note there are ‘Statutory’ variations to the inormation

shown in this publication in respect to;

• EnglandandWales: TheBuildingRegulations2010and Approved Documents.

• Scotland: TheBuilding (Scotland) Regulations2004 (as

amended)andtherelevantTechnicalHandbooks.

• NorthernIreland:TheBuildingRegulations(NorthernIreland)

2000 (as amended) and the relevant Technical Booklets

please reer to your Premier Guarantee Site Audit Surveyor

or urther advice.

Your Premier Guarantee Site Audit Surveyor contact is

Contents

Superstructure

Construction o wallsMortar

Masonry durability

MasonryWalljunctions

Cavity walls

Cavity wall insulation

Movement in masonry

Preventing damp penetration at external openingsStructural Lintels & bearings

Parapets

Lateral restraint o walls by foors and roos

Wallplates

Chimney construction

Horizontal damp proo courses

1 2



Superstructure

Construction of walls

Set out walls using securely marked proles with•

reerence lines and datum levels.

Walllengthsmustbecheckedforsquareness. •

Cross check against diagonal measurements rom•

the Architect plans.

The position o openings must be anticipated to•

ensure correct and even bonding occurs both

horizontally and vertically.

Care should be taken to avoid overstressing mortar •

by a building rises o no more than 1.5 m in a day.

Both leaves o a cavity wall should be built at the•

same time to avoid incorrect coursing and potential

weakeningofanindividualleaf(ifleftunsupportedfor

anylengthoftime).

Wheremasonryistobeplasteredorrendered;raked•

outjointsapproximately15mmdeepshouldbe

provided as work proceeds, to give a good key.

Laying bricks and blocks

Good building practice must be ollowed

Lay bricks and blocks level, using a regular bond with•

anominal10mmhorizontalbedjointprovided(unless

otherwisespeciedbythedesigner).

Fillcrossjoints. •

Perpendjointsshouldnotbelessthan7mmwideand•

ully bed in mortar. The perpends should be kept

vertically aligned as the work proceeds.

Lay ‘rog’ bricks with ‘rog uppermost’ lled with mortar •

to ensure the wall is stronger and more resistant to

sound transmission.

Lay hollow blocks on shell bedding with the vertical•

jointslled.

Ensureaconsistentbond,especiallyatcorners. •

Walltiesmusthavenotlessthan50mmdepthof•

bedontothemortarjointafterallowingfortolerances.

Ensurethemortarjointsarecarefullystruckaswork•

proceeds to prevent the cavity and or insulation below

being lled with mortar droppings.

Case study

In the picture below the bonding is inconsistent resulting in

verticaljointstocoincideonconsecutivecourses.Thewall

ties are also not properly bedded into each lea o masonry

using the correct type and length.

3 4



Horizontal and vertical alignment o masonry walls

Dimension Permissible

Deviation

Straightness in any 5 m length + / - 10 mm

Verticality up to 2.5 m height + / - 10 mm

Verticality up to 7 m height + / - 20 mm

The above dimensions represent the level that can be reasonably

achieved or general brick and block work masonry.

Case study

The vertical alignment o the load bearing inner lea o block work

in this case was ound to exceed the above recommendations.

Chases in masonry leas

Do not;

cut chases into any block masonry which is less than•

75mminthickness.

cut horizontal or raking chases in solid walls to a•

depth greater than one-sixth o the thickness o the

lea.

cut vertical chases to a depth exceeding one-third the•

thickness o the single lea in solid walls.

cut chases in separating walls.•

Chasesoneithersideofawall(notaseparatingwall)mustbeoset by a distance at least equal to the wall thickness.

Case study

A horizontal chase to accommodate piping was ound more

than 30 mm depth, approximately a 600 mm above the foor

level. This exceeded the maximum allowed by nearly double.

Cracking in the block work was observed above and below thechase.

5 6



Buttressing walls and returns

Wallsshouldhaveappropriatestructuralreturnsandpiers

to give adequate stability that meets the current Building

Regulations.WallthatdonotmeetcurrentBuildingRegulations

guidance should be proven by structural calculations.

Mortar

General requirements

Masonry mortar should be selected according•

to exposure conditions o the masonry and the

specication o the masonry units

Calcium chloride, ethylene glycol, or admixtures•

containing these materials, should not be added to

mortars to provide protection against reezing, or or

any other purpose.

Do not use air, entraining or other admixtures•

unless specied by the designer and ollowing the

manuacturer’s recommendations.

Wheremortarstrengthisrequiredforstructural•

reasons careul consideration should be given to the

accommodation o movement.

Mortar must not be ‘knocked up’ when it has begun•

to set.

Mixing in cold weather

Do not mix mortar when the air temperature is at or below 2 °C

andfalling.Donotuseneaggregate(sand)orsemi-nishedmortar(lime-sandmixtures)containingiceparticles.

Hot weather working

Whereprolongedperiodsofhotweatherpersist,certainclay

bricks(whicharehighlyabsorbent),maybewettedtoassistin

reducingsuction.Wettingshouldnotbeundertakenonany

other type o brick, nor should saturating completed walls be

attempted.

Site batched mortar

Caution must be taken when mixing material on site. Gauging

volumes by the shovelul must not be relied on to give

suciently consistent mix proportions, particularly with saturated

materials(e.g.dampsand).Thiscanresultinvariations

between batches which may aect the strength & durability o

the mortar. It is recommended that site batched mortar mixing

should only be produced using a careully selected prescription

mix and a suitable mechanical mixer.

Additives

Plasticisers and other additives may be added to the mortar mix to improve workability. Only products that have been specically

designedasamortaradditiveshouldbeused.Washingup

liquid and similar products must not be used.

Pre-mixed mortar

The use o pre mixed or actory made mortar ensures

consistency throughout the build element. It may be produced

as complete or semi-nished mortar. The design teams

approved specication must be ollowed ensuring that the

mortarconformstoBSEN998–2.

Table o mortar mixes

The mixes in the table below are recommended or clay bricks

(unlessotherwiserecommendedbythebrickmanufactureror

theEngineer/designerfortheparticularsite)

Use Required

Exposure Recommended Proportion

by Volume

Mortar

designationto BS 5628

– 3 And

BS EN 1999

– 2 :2006

Cement

: Llme :

sand

Cement

: sand

with air

Masonry

cement :

Sand ***

Work below

or near

ground level

High

Durability1* : ½ : 4

to 4 ½

1* : 3 to 4 1* : 2 ½ to

3 ½

(ii ) **

Internal and

External

wall areas

above

DPC level

General use 1 : 1 : 5

to 6

1 : 5 to 6 1 : 4 to 5 (iii)

High

Durability –

Severe or

Very Severe

exposure

1 : ½ : 4 to

4 ½

1 : 3 to 4 1 : 2 ½ to

3 ½

(ii)**

Copings,

cappings

and sills

Low

permeability

jointing

1 : 0 to

¼ : 3

Use a type

S sand to

BS 1200

- - (i)**

Parapets

and

Chimneys

High

Durability1 : ½ : 4 to

4 ½

1 : 3 to 4 1 : 2 ½ to

3 ½

(ii)**

7 8



For Minimum Compressive strength of site mixed mortar at 28 days

– see Table 13 BS 5628 – 3

When referring to Tables 13 in BS 5628 - 3 see also BS EN 1996

– 2 :2006

Where Concrete or Calcium silicate bricks are used, the manufacturer’s

recommendations must be followed and a designation (ii) or (iii) mortar

may be required

* Where soil or ground water sulphate levels are present, use Sulphate

resisting Portland cement (to BS 4027)

** Where Potential High risk of saturation is likely, refer to Table 12 in BS

5628 - 3

*** For Masonry cement :sand with Lime ller - see Table 13 BS 5628 – 3

Masonry durability

Masonry can become saturated with water, the extent o which

depends on the level o exposure. High areas o risk include

Masonryaroundtheexternalgroundlevel(two•

courses above and below are the most vulnerable

areas).

Parapets; especially where it is not rendered and / or •

the parapet is not provided with an eective coping.

Unrendered chimneys.•

Cappings, copings and sills in areas where reezing•

conditions may occur.

Wallswithminimalroofoverhangs. •

Local climatic conditions or geographical locations•

where elevations are exposed to severe wind driven

rain.

Buildings within severe exposure areas are required to have

rost resistant brickwork.

TheBSEN771seriesspeciesthecharacteristicsand

perormance requirements or masonry units.

WhereConcreteblocksaretobeusedeitherbelowDPC

level or externally without a render nish, reerence to the

manuacturer’s specications including third party accreditation

is required to conrm adequacy.

Cold weather working

Do not:

Build masonry when the air temperature is at or •

below 3 °C and alling, or until it is no less than 1 °C

and rising.

Lay mortar on rozen suraces•

Use wet bricks or blocks when there is a danger o •

reezing

Do:

Ensurenewlybuiltworkisprotectedfromrain&frost•

with suitable waterproo sheeting

Recessed mortar joints

Recessedmortarjointsarenotrecommendedfor:

Externalwallsinclaybrickworkormasonrycavity•

walls in areas o severe or very severe categories o

exposure

Or

Cavity walls with ull ll cavity insulation.•

Masonry wall junctions

New dwellings next to existing dwellings

Whenextendingontoexistingpropertiesthereistheriskof:

dierential movement occurring.•

water penetration through to the internal nishes at•

thejunctionofthenewandexistingwalls,particularly

whereacavitywalljoinsasolidmasonrywallor

anothercavitywall(withoutcontinuationofthecavity).

Whereanewdwellingistobeconstructedabuttinganexisting

dwelling, the new home should be an independent structure

with a new wall constructed alongside the existing wall. The

wall should be supported on a new oundation, independent o

the existing building.

Internal masonry wall junctions (new dwellings)9 10



Whereamovementjointisnotrequired:

alternative courses should be toothed•

or

wheretheadjoiningblockwall(e.g.separatingwall)is•

adifferentdensity;abuttjointisrecommendedwith

suitableties(orsuitableequivalent)at225mmmax

vertical centres.

For sound insulation requirements ol low the design team’s

proposal careully.

Newbuildextensionsontoexistingbuildings(i.e.aspartofa

refurbishmentprojectwithnewextensions)

It is not sae to assume a proprietary connector will be

satisactory or all cases.

Older buildings tend to have shallow oundations which move

seasonally in clay soils without damage. Damage is likely to

occuratthejunctionofanoldermovingbuildingandanew

building with oundations meeting current standards.

Prior to starting work on extensions an assessment o the

ground conditions and the existing oundations are required to

determine:

the extent o oundation movement likely to occur and•

what remedial measures are required to strengthen

the existing building and oundations.

the type o connections required between the new•

andexistingstructures(e.g.atwalls,roofsbeams

etc.).

In all cases o extending onto existing buildings

theexistingwall(aswellasitsfoundations)mustbe•

proven to be structurally stable and able to take any

additional load imposed on it.

the orm o connection between the structures•

must be proven by a structural engineer to cater or

movement.

horizontal DPC’s rom the new build must link through•

totheexistingstructureDPC(ifnone,achemical

injectionDPCwillberequired)

the method o preventing water penetrating at the wall•

connections.(seerecommendeddetailsoverleaf)

in the situation that the existing wall becomes a•

separatingwall(e.g.apartments),thewallwillrequire

upgrading to achieve at least 1 hour re resistance

the separating wall must also meet sound insulation•

standards. Robust details do not exist or these

constructions.

Case study

Anewcavitywallextensionformedajunctionwithanexisting

solidwalledbuildingaspartofaconversionproject.

Aproprietaryjunctionplatejoinedthestructures•

without regard or the extent o movement likely to

occur.

The existing solid brick wall orms a direct path or •

dampness to bypass the cavity wall and reach the

internal nishes.

Thiswallwasrebuilt(duetopoorworkmanship)andan

independent lining provided to the existing gable and new inner

lea to ensure no damp penetration or cold bridging occurred.

New cavity wall to existing solid wall junction

11 12



(reurbishment projects)

New cavity wall to existing cavity wall junction

(reurbishment projects)

Cavity walls

Construct the cavity wall with the correct cavity width.•

Ensurethecorrecttypeandlengthofwalltieisused. •

Ensureexistingcavitywallshaveadequatewallties. •

Cleanoffanysurplusmortarfromjointsonthecavity•

aces as the work proceeds. Keep the cavity and wall

ties ree rom mortar and debris.

Draw battens should be used to keep the cavity clear •

o mortar and debris.

Cavities at the base o the wall should be kept clear.•

A minimum 50 mm clear cavity is required between•

partial ll insulation and the external lea.

Case study

Debris build up on cavity wall ties can result in damp

penetrating the inner ace o the wall.

Cavity wall ties

OnlywalltiesinaccordancewithBSEN845–1,•

must be used. Other types must be independently

third party accredited and submitted to the warranty

provider or approval beore use.

Stainless steel wall ties should always be used.•

The correct type o tie depends on; the structural•

requirements o the wall, the insulation to be used and

the resulting cavity width. The contractor must ollow

the Design team’s approved plans.

13 14



Thewalltiesmustbelaidtoensure:

Thecorrectspacingisachieved(seechartoverleaf). •

not less than 50 mm embedment o the wall tie onto•

each lea must be achieved.

the ‘drip’ is in the centre o any clear cavity.•

the two leaves o the wall must be coursed to ensure•

the wall tie slightly slopes down towards the outside

lea and the drip points downwards.i partial ll insulation is to be installed, the correct•

combination o wall tie and retaining disc must be

used and a 50mm clear retained cavity provided.

Wall tie specication

WalltiesshouldconformtoBSEN845–1

Unlled or fully lled cavities

50mm to 75mm wide Buttery

Double triangle

Vertical twist

Proprietary ties *

75mm to 100mm wide Double triangle *

Vertical twist

100mm to 150mm wide Vertical twist

Partial lled cavities

50mm to 75mm wide Double triangle with proprietary

retaining disc Double triangle

with integral retaining rod

Proprietary ties *

75mm to 150mm wide Vertical twist with proprietary

retaining disc

* Third party accreditation should be provided

Walltiesmustbebuiltinasworkprogresses.Walltiesmust

notbepushedintothemortarjoint.

Spacing o wall ties

TiesshouldbespacedtotherecommendationsinBSEN

1996-2:orfollowthestructuralengineersdesignifwallties

require more requency.

Be aware:

Walltiesmustnot be allowed to all backwards to the inner lea.

15 16



Insulation should wrap around corners and not be cut•

andjoined.

Do not leave gaps in the insulation. Butt the insulation

slabstogetheratbothhorizontalandverticaljoints

and at closures, and install them with staggered

verticaljoints.

Keepjointsbetweeninsulationslabscleanandfree•

rom mortar droppings. Do not place any small o-

cutswiththecutedgeagainstthewallsurface(i.e.

placedatrightangles).

Ensurehorizontaljointsofinsulationcorrespondwith•

horizontalrowsofties.Whereadditionalwalltiesare

required, cut insulation slabs neatly to accommodate

them.

Case study

Insulation batts were ound incorrectly pushed into the cavity

with cut edges acing the outer lea.

Blown or injected cavity ll

Blownorinjectedinsulationshouldbecarriedoutby

appropriately qualied personnel. The cavity must be inspected

priortotheinstallationtoensure:

mortarjointsareushwithinthecavityandtheinner•

aces o the masonry are clean.

the cavities are ree rom obstructions such as lumps•

o mortar and parts o bricks. Mortar droppings below

the horizontal DPC must be minimised.

all scaold holes are lled with mortar on removal.•

Be aware

Thecorrectlengthofwalltiemustbeusedappropriatefor:

the width o cavity.•

the type o insulation used.•

to ensure a minimum 50mm bed onto each•

lea is achieved.

•

•

Do not attempt to tie wall ties together to achieve the

correct length.

Cavity wall insulation

Full ll cavity insulation

May not be appropriate in area with high or severe•

weather exposure.

Should not be used with random sandstone walling or •

other irregular acing.

Recessedmortarjointstotheouterleafarenot•

recommended with ull ll insulation.

Only third party accredited insulation products should•

be used.

Insulation batts should be built into the cavity as work •

proceeds and not pushed in ater.

The insulation slabs are o a thickness appropriate to•

the cavity width so as to correctly ll the cavity.

17 18



recessedmortarjointstotheouterleafarenot•

recommended with ull ll cavity insulation.

Partial ll insulation

Third party accredited Insulation slabs must be used.•

A minimum 50mm clear cavity between partial ll•

insulation and the external lea is required.

The correct combination o wall tie and retaining disc•

must be used and installed in accordance with third

party accreditation recommendations.

Keep the tops o the insulation batts clean and ree•

rom mortar droppings beore the next batt is installed.

Case study

Partial ll insulation batts were poorly installed against the inner

lea, the remaining cavity was less than 50mm and bridged

by mortar droppings allowing a path or water to reach the

inner lea.

Movement in masonry

Movement joints

The design o masonry walls should include provision or

potential thermal movement ater construction. A structural

engineer must be consulted to provide a specication.

Verticalmovementjointsshouldrunthefullheightof•

the wall.

The type o compressible ller and sealant to be•

used must be able to accommodate expansion

and contraction movement whilst resisting water

penetration. The sealant should conorm to BS 6213.

Walltiesmustbeprovidedat300mmvertical•

spacingseithersideofthemovementjoint.

Theconstructionofmovementjointsshouldberobust•

tomeetrequirementsofBS5628-3:2005&BSEN

1996-2:2006.

Inexternalwallscontainingopenings,movementjointsmay

be needed at more requent intervals, or the masonry above

and below the opening may need to be reinorced in order to

restrain movement.

Atypicalmovementjointinanouterleafofbrickworkisshown

below:

19 20



Masonry type Maximum spacing of

movement joints

Clay brickwork 12m centres

Dissimilar clay and concrete units

e.g. feature panels where different

movement characteristics possible

The brick manufacturers

should be consulted as more

frequent spacing likely

Short returns in clay masonry If a return in the length of

clay masonry is less than

675mm and either adjoining

length of masonry exceeds

6m, the masonry should be

interrupted at the return to

prevent the development of a

‘mechanical couple’ and the

risk of cracking.

A vertical, compressible joint

or a “slide-by” detail should

be incorporated.

Calcium silicate masonry Should be designed as a

series of panels separated

by movement joints at 8m

intervals.

Aggregate and autoclaved concrete

masonry

Vertical joints to

accommodate horizontal

movement should beprovided at intervals of 6m

Natural stone masonry In the absence of specic

calculations, vertical joints

not less than 10mm wide

should be provided at

intervals specied by a

structural engineer and

located no more than 8m

from an external corner

Internal leafs of cavity wallsThe masonry block manufacturer must

be consulted

In rooms where any walllength exceeds 6.0m

Note: 3mm must be added to the above i the rame is

supportedoffasuspendedtimbergroundoor.Engineered

timber members oer a slight reduction in shrinkage or urther

advice reer to a structural engineer or advice.

In calculating the amount o movement allowance must also be

made or any compressible sealant used. The material used or

lling these gaps should be capable o easily compressing to50% o its original thickness. Guidance on the type o sealants

to use is given in BS 6213

Allowance or ventilation to the cavity will also be required.

Preventing damp penetration at

external openings

Typical section through a window reveal

(Lintelnotshownforclarity)

21 22



A Weepholesat450mmcentresmustbeprovidedwithat

least2(oneateachend)ofthecavitytray(excluding

rendernishes)

B Full height insulated cavity closure incorporating a

verticalDPC.

C ThecavitytrayshouldprojectbeyondtheverticalDPC

D SillDPC(ifprovided)mustturnupbehindtheverticalDPC

by at least 100mmE Stop ends must be provided to the cavity tray weep holes

Moisture penetrating through the outer lea o cavity walls

(fairfacedbrickworkorrenderedblockwork)willrundownthe

inner ace o the external lea.

Wherethecavityisbridgedbyabarrier,e.g.lintels,oorslabs,

concrete rame members or horizontal cavity re barriers, a

cavity tray and weep holes are necessary.

Weepholesmustnotbeblockedparticularlywherearender

external nish is applied to the wall.

Window / door reveal vertical DPC sheltered

to normal exposure

Severe to very severe exposure

Bay window opening

23 24



Recessed balcony opening

Cavity trays

Cavity trays are required to span over openings in the cavity

wall where door and window openings, meter boxes, ducts and

cavity barriers are constructed. They are also required where

roo structures abut external cavity walls. This is to avoid water

penetrating through the outer lea and reaching internal suraces

at lower levels e.g. bay window sots.

Over structural openings in external walls

25 26

Partial ll cavity insulation is shown in this example.

The cavity tray must be ully supported within the•

cavity and lapped onto the ull width o the inner lea.

The height o the cavity tray must be at least 150mm•

within the cavity.

Stop ends must be ormed at each end and weep•

holes provided in the outer lea to drain moisture out

o the cavity.

At pitched roo abutments



27 28

Detail o fashing construction where external

walls are rendered

Detail36:IrelandtechManualdetailbackgroundwillbe

removed keep text but see note ** below

Lean-to roo abutment cavity tray construction

Flat roo abutment cavity tray construction

The external render to the block outer lea is not

shown or clarity.

Partial ll cavity insulation is shown in this example

Structural Lintels and Bearings

Lintel bearings

Construct a ull masonry unit immediately below lintel•

ends. Do not use o-cuts o bricks or blocks.Ensurethelintelislevelandisbeddedinmortar. •

The length o lintel bearings should be not less than•

100 mm and not less than 150 mm or pressed steel

lintels.

Certain lintels may require to be propped until the mortar has

set under the bearings.

Whereprestressedandreinforcedconcretelintelsareused:

build in lintels with the correct side uppermost in•

relation to the position o reinorcement.

prop prestressed composite lintels at centres not•

exceeding 1.2 m during the construction o masonry

above.

when using composite lintels o prestressed concrete•

with masonry the masonry should be careully built

withsolidlylledjoints.Noholesforservicesorweep

holesshouldbemadenorshouldanything(e.g.cavity

tray)bebuiltintothemasonrywithinthecomposite

zone.

exposed aces o lintels must be provided with re•

protection.



Unless proven by a structural engineer point loads immediately

above a lintel must be avoided.

Case study

Wheretheundersideoflintelsareexposedaboveopenings

such as garage doors, the lintel must be adequately protected.

Pad stones

Pad stones must be built into the wall to receive the•

ends o the structural member.

The size and material to be used or the padstone•

must not be less than the structural engineer’s

specication.

Pad stones must not bridge the cavity o an external•

wall.

Parapets

The minimum thickness and maximum height o parapet walls

shouldbeasbelow:

Thickness (mm) Parapet height not to be more than (mm)

t1 + t2

equal or less than 200 600

t1 + t2

greater than 200 equal or

less than 250 860

ADPCunderthecopingandacavitytrayattheroofjunction

must be provided to prevent dampness reaching the inner lea

in the accommodation below. Cavity insulation not shown or

clarity.29 30

L t l t i t f ll b fl d f Timber foor / wall detail



Lateral restraint of walls by floors and roofs

Whereoorsandjoistsare“builtin”orsupportedbyhangersoff

thewall:

shrinkageofjoistsshouldbetakenintoaccount. •

members must be secure to prevent twisting.

whereappropriatejoistsshouldbeprotectedagainst•

moisture.

gaps ormed in the wall construction should be sealed•

with a compressible ller to ensure air tightness.

Thebearingsofalloors,joistsandroofmembersmustnotbe

lessthan90mmontoaloadbearingwall.

Wherewallsrequirelateralrestraintbytensionstrapsatoors

androofconstructionstheprovisionsinBSEN1996-2:2006

should be met as well as the requirements ound in current

Building Regulations.

It should be noted that lateral restraint straps are not only

required at foor and rater / fat roo member levels but may

alsoberequiredtobettedatceilingjoistlevelinapitchedroof

situation. Provision is necessary when the height o the wall

exceedsrecommendedvaluesfoundinBSEN1995-1-1:2004

and current Building Regulations.

Ensureallrestraintstrapsttightlyagainstthemasonryface

within the cavity.

Provision should be made or blocking to be used in the gap

betweenthejoist/rafterandtheparallelwallatalllateral

restraintstrappositions–aswellasinbetweenjoist/raftersfor

the length o strap required.

Lateral restraint straps at foor or roo level must not be retro

tted by plug and screwing the strap to the masonry.

Timber foor / wall detail

Suspended concrete beam and block foor / wall detail

Timber roo / gable wall detail

Whereroofsarerequiredtogivelateralrestrainttowalls,

referencetoBS5268–1–2005&BSEN1990:2002should

bemade.(Seepreviousnoteaboutprovisionatceilingtielevel).

Restraint straps must turn down the cavity by at least 100mm

and be tight against the ace o the wall.

31 32

Case studyRater / gable wall detail



Case study

Whereinllingisrequiredbetweentrussmembersasshown

belowawallplateshouldnotbeusedandthejoistsshouldbe

“builtin”oronsuitablehangers.

Block work has been incorrectly built o the timber wall plate

instead o the trusses being supported o the masonry by correctlyspeciedtruss/joisthangers.

Chimney constructions

Chimneysmustbeconstructedsothatitsheight(measured

fromthelevelofthehighestpointinlinewiththeroof)should

not be greater than our and a hal times its least width.

Thecorrectprovisionofashingsareprovided(seedetails).

33 34

Rater / gable wall detail

Case study

The lateral restraint straps were ound to be securely built

into the gable wall but were not mechanically xed to the roo

members.

Wall plates

Wallplatesmustbelaidlevelonabedofmortarandxed

down onto the wall to restrain the roo against displacement

with galvanised straps at no greater than 2m centres.

Flues and linings Horizontal Damp Proof Courses



Flues and linings

General

Fillalljointswithjointingandcaulkingmaterials•

in accordance with the manuacturer’s sitework

instructions.

Build socketed fue liners with the inner surace•

oftheliningsmoothatthejointsandsocketends

uppermost, i necessary.

Fill the void between brick chimneys and clay or •

concrete fue liners with lightweight concrete or weak

mortar.

Do not use cracked or broken liner sections. Form•

bends with purpose made ttings.

ExtendleadorproprietaryhorizontalDPCtraysthroughtheliner

intotheueandturnupwards(seefollowingdetail)

The construction o fashings is dictated by the type o roo tile

/cladding to be installed. Please reer to the roo tile /cladding

manuacturer’s details or specic fashing detailing.

35 36

Horizontal Damp Proof Courses

Installation o the DPC must ollow normal good practice or the

detailingofDPCs,assetoutinBSEN1996–2:2006,BS

8000-3:2001&BS8215.

EnsuretheDPMisturnedupatslabedgeandlapped•

under the DPC or the ull thickness o the inner lea to

formacontinuousbarrier(includingunderdoorsills).

The DPC should be laid on a smooth bed o resh•

mortar in a continuous length or the ull width o the

lea including any nishes e.g. external render.

Ensureatleasta100mmoverlapisprovidedatany•

jointorangle.

The DPC must not obstruct the cavity.•

EnsuretheexternaledgeoftheDPCisvisibleandnot•

bridged by mortar when completing pointing o the

mortarjoint.

ExternalrendermustnotbridgetheDPC. •

Ensuretheleanmixcavityllmaterialisatleast•

225mm below the DPC level.

DPCs must not be pierced by services or xings.•

Case study

Blue bricks should not be used as the sole means o preventing

damp. A proprietary DPC must always be provided.

(Note;Poordetailingoftheoorslabconstructionatthedoor

thresholdpositionhasalsoresultedinacoldbridgingissue)

Case study



37 38

Insert Photo 1

Stepped DPC

WhereaslopingsiteconditionexiststheDPCmayhavetobe

stepped.

The DPC must be stepped in the masonry coursing so that

at any point it is never less than 150mm above the nished

ground level.

Render / Horizontal DPC junctions

Render must not be taken below and bridge the horizontal

DPC. A proprietary render stop must be installed to terminate

the render above the DPC.

Ca y

NotonlyhasthehorizontalDPCbeenbridgedbytherender

it has also been damaged by the insertion o waste pipes. All

service penetrations should be neat and above DPC level.

Insert photo 2

Note:Surroundingaccesspathsmustnotbeconstructed

at the same level as the DPC. Disabled Access ramps andlandings should be kept 150mm away rom the wall.

DPC / Radon / Gas membrane cavity trays

Whereagasmembraneisinstalledacavitytraywillberequired

to be ormed across the external walls. Typically the gas

membranewillalsoformacavitytraydetailasfollows:

Case study Avoidance o mortar build in cavity trays applies at all levels;



39 40

y

The cavity tray must be at least 225mm in vertical height and

lap ully across each lea o masonry unlike the example below.

The correct type o membrane must be used and correctly

lapped with the DPC.

Case study

Care must be taken to avoid excessive debris building up in the

tray or allow the insulation to become dislodged and bridge the

cavity.Waterpenetrationandcoldbridgingtotheinnerleafis

likely to occur.

horizontalDPC/DPMjunctionsandatupperlevelswhere

lintels, re stopping and roo abutments occur.

Notes Notes



41 42

Notes Notes

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