\ ...... .J,")l/ \

) ~ ,,'I ( /I

DESIGN NOTE

J

, oY J.

-f (

" (.'1 v

<,i. {

.I

/

) ,,! rT> rJ ~ ) ',V (J e· /: ' I, 'J

. \ ,:-- ,Published by the Brick Development Association

" I ~ )I , )\

') , .) , r r / ( J V\ ,\ / C

) I , '\ • ' t f, .RESIS~ING , R,Al~j P~~ETf..A ~I~N

<L WITH"FApING~ .BRICKWORK1 . ' ~ 7 )\• I Michael Hammett Dip Arch ARIBA J 1

~ ~ •• ~ ~ " 1

f >J.../) .' ) , \

'(I

(

i )

if

t If

/

CONTENTS

PAGE

INTRODUCTION

SCOPE

... 3

3

DESIGN PROCEDURE · ASSESS AND SELECT 4

ASSESSING EXPOSURE FOR SPECIFIC LOCATIONS .... 4

6

7

............................... . ........ ................ 7.. 8

88

........... ........ . 9. 10

.. 12...... ......... ............ ............... .. 13

SELECTION OFMATERIALS AND CONSTRUCTION TO RESIST WIND·DRIVEN RAIN

1 TYpe of brick . .2 Mortar composition .

3 Thickness of leaf4 Cavity walls .5 Width of air space within any cavity6 Mortar joint, profile and finish .7 Cavity insulation "'

8 Architect ural features and local practice .9 Applied external surface finishes ..10 Quality of workmanship to be achieved on site

DAMP PROOF COURSES AND CAVITY TRAYS

...............14

.......... 14

... 15... 15

................................................................ 15....... .. 15

General

Perfonnance .

[unctions ..

Continu ity and support ..Resisting rising damp

Immediately above ground levelBelow ground level .

Controlling downward movement of wat er

Cavity walls .... 16

Overopenings . 16

Arches .. 16Stop ends .. .. .... 17

Weepholes .. 17Requirements for damp proof cou rses and cavity trays for specific parts of buildings

At jambs to openings .. .. 18

Sills .. 19Requirements for additional cavity trayswith cavityinsulation 19External wall becoming an internal wall .. . 20Parapets .. 20Copings and cappings 21Chimneys 22Structural frames . . . . 22Flashings and weatherings .. 23

........................ 23

................ ..... ..... ............... ............. 23

....................................... 24

7

10

.......... 15

.. 5Classification of exposureto local wind·driven rain , .

Minimum thickness of solid brickwork walls, with and without rendering,to resistrain penetration in various categories of exposure..

Thermalinsulationmaterials forusein cavity insulated walls

Summary of materialsusedfordamp proofcourses and cavity trays

Table 3

Table 4

CONCLUSION

REFERENCES

ACKNOWLEDGEMENTS

TABLES

Table 1

Table 2

Brickwork has been a dependable form of

construction for weather resistant walls for

hundreds of years, but conventional bricks andmortarsarenot themselves waterproof.

Moisture may penetrate brickwork by diffusing

throughmicroscopic voidsin the materials, or bypercolating or flowing into and through hairline ormore noticeable cracks in the fabric. The

effectiveness ofa solidbrick wall in resistingpenetration by wind-driven rain is in direct

proportion to wall thickness. Traditionally, forbuildings in locationswhere greater severity of

exposureto wind-driven rain is experienced. thickerwallsareused compared with those for buildings inmore sheltered situations.

In the mid-nineteenth century therewas

considerableinterest in the construction of low-costhousingforworkers. Economy ofmaterial wassought, but thinner walls equated with reduced

The resistance of masonry to wind-dnven raininvolves assess ing performance relative toanticipated exposure, as opposed to achieving anabsolute condition of its being waterproof.Thispublication examines and comments on the relativesignificance of the various factors that need to beconsideredwhen assessing exposureand thenspecifying an appropriate wall construction for any

particular application.

Solid brickwallconstruction is considered andalso the protection offered by rendered finishes is

acknowledged, but the publication concentrates onthe deta ildesign and specificat ion of cavtty walling

INTRODUCTION

resistance to rain penetration. This shortcoming ofsolid walls led to expe rimentation with hollow wall

construction by the use of part icular bonding

arrangements such as rat-trap bond, Silverlockbond and Dearne's bond and also by the

development of patent hollow bricks. However, the

most significant development was the introductionof double-leaf cavity walling. By the twent iethcentury this technique had become esta blished and

by the' 930's it was widely used in housing.

The design of the cavity wall accepts that solidmasonry subjected to wind-driven rain will not beabsol ute ly waterproof but is capab le of providing

substantial resistance to penetration. To divert thepassage of any moisture that may pass through the

externalleaf of the wall the cavity is introduced todrain it down and out again to the exterior.This ensures that waterwillnot penetrateto theinternal leaf of the wall causing dam p cond itions

within the building.

SCOPE

with an outer-leaf of fairface brickwork. The effectsof incorporating thermal insulating materials withinthe cavity arealso examined.

As damp proof courses and cavity trays areessential components incorrectly detailed cavitywall design, guidance is included on theirspecification and installation.

With an understanding of the constra ints and

opportunities that attend differences inseverityofexposureand in the performance of diverseconstruction features, a designercan exploit thegreat choice offered by brickwork to provide

effective protection and attractive appearance.

DESIGN PROCEDURE - ASSESS AND SELECT

Because the performance of a specific form of

wall constructionhasbeen satisfactory in aparticular locality it must not be assumed that it

will be equally suitable in other regions. Design and

specification assumingworstcaseconditionsmay

be considered to provide notionaluniversalapplications, but for the majority of buildings on the

majority of sites such a basis for the choice of

construction would be un justifiably restricted and

lead to unwarranted expense.

The acknow ledged procedure is to assess the

severity of exposure that is experienced at thelocation of the proposed building and then select

and specify a construction to provide the

appropriate resistance to rainpenetration.

folloWing this methodical approach a

construction thathas relatively low resistance torain penetration maybe quiteacceptable in asheltered locatio n, but be who lly inappropriate

where more severe conditions areanticipated.

Location. site factorsandbuildingdesigncan increase the anticipatedseverity01exposure, but evenso, well consideredcavitywall construction can beeffective

ASSESSING EXPOSURE FOR SPECIFIC LOCATIONS

Assessmentofexposure to wind-driven rainshould be regarded as a necessary and worthwhile

first step in the des ign proced ure. When

determining the likely expos ure of a building, the

most exposed part shou ld be given particular

attention andthis mayaffect decisions concerningthe choice of design and materials for the whole of

the building.

Having determined the level of risk likelyto be

experienced the designer, using the guidance on

resistance to rain penetrationof differe nt formsofconstruction and the factors affecting rain resistancedescribed in this Design Note, should select the

materials and form of construction that together

will provide adequate performance, paying due

regard to the importance of correct detailing and

appropriate standards of workma nship .

In 1976 the Building Research Establishment

Report Driving Rain Indez.' 1proposed a method

of assessing the quantity of rain falling on a verticalsurface such as a wall. Annualrainfall and average

windspeeds recorded at various meteorologicalstations throughout the United Kingdom could be

used in calculationsto determine driving rain

indices relative to the geogra phical locations of

proposed building sites. This method demonstra tedthe widevariation ofexposureto wind-driven rainexperienced nationally, but it was of limited

practical value because of the rathergeneralisednature of the dataandthe assessment method.

Collection of data continued in the 1970's

and1980's and with the benefit of computeranalysts the Meteorological Office was able to

produce improved data, based on the observa tion

that prolonged rainfall was usually associated with

stronger thanaverage winds.

A more refined and realistic method of

prediction was eventually developed and publishedby the British Standa rds Institution as BS8104

Bri tish Standard Code ofpractice for Assessingexposure of walls to wind-driven rairP I. lt allows

calculationsof driving rainfall for different

• Basedanexposure zonesdefined inBREReportBR262

• Maximumwallspell indexcalculated usIng the/oca/ spellIndex methodspecifiedinBS 8104

orientations. It alsoallows annualaverage values to

be calculated as wellas quantities forthe worstlikely spellin any three year penod.

Rainfall varies considerably across the countrybut is largely unaffected by local features.Conversely, the general windspeed does not changemuchacross the country but It is affected

significantly by local features such as the spacingand height of neighbouling trees and buildings andwhether the ground is flat or rises steeply.

BS B104 permits corrections to be made forground terrain, topography,local shelter, and theform of the building concerned. These factorscan

havea majoreffect on the calculations and it is

important to recognise that , because of theirinfluence,within any geographical localityconsiderable variation of exposure canbe expected

from site to site.

BS 8104 gives recommendations for two

methods of assessing exposure of walls in buildings

to wind-driven rain, namely the local spell indexmethod and the locol onnuol index method. Thelocol spell Index method should be used whenassessing the resistance of a wall to rain

penetration. The locol onnuol index is intended forusewhen considering the averagemoisture content

of exposedbuilding material or when assessing

durability, weathering and likely growth of mossesand lichens.

Categoryof Exposure »

2

3

4

Sheltered

Moderate

5evere

Very severe

Colculatedquantity ofwind·driven rain· {/it1f!$Im2 P'"~

Less than33

33 to less than 56.5

56.5 to less than 100

More than 100

Table 1 gives exposure categoriesdefined in

terms ofwoll spell indices calculated using the locolspell index method specified in BS 8104. Theindices, denved as they are frominherently variablemeteorological data, should not be regarded asprecise.Where assessment produces an index nearthe borderlinethe designer should decide which isthe most appropliate category forthe particularcase, using local knowledge and experience.

Table 1 is based on the 4 exposure zone series

defined in BRE Report BR 262 Thermal insulation:avoiding risksl31, which simplifies the 6 categoryseries specified in Table 10 of BS 5628 : Part 3British Standard Code of practice for the use of

masonry : Materials and components, designand workmanship4J. As canbe seenin Table 1

there are nooverlaps in the definition of the 4

categories. Considerable overlaps in the definitions

of the 6 category series caused some confusion and

uncertainty of interpretation. TheBR 262 series is

thereforegenerally considered to be an

improvement on the BS 5628 : Part 3 selies.

BR 262 provides a simple procedure forassessing exposure to wind-driven rain forwalls up

to 12 m high. It is plimalily intended for low risedomestic buildings but may also be consideredsuitable forother categories of buildingsof similar

scale.

The simplified guidance is based on a mapwhichdefines zones in which similar exposure

conditions are predicted. Thepredictions are basedon calculations in accordance with BS 8104. The

zones arenumbered 1 to 4 and correspond with

categolies Shelteredto Very Severe as noted in Table 1.

The calculations defining the mapped zones in

BR 262 assume "worst case" conditionsand so

provide very conservativeguidance. Using the BR262 map to predict exposure restlicts the choice ofconstructionbecauseit is not able to identify sites

withineach zone which may benefit fromshelterthat considerably reduces exposure to wind-drivenrain. Greater choiceof construction is justified bythe more specific assessment possibleby fcllowingthe B5 8104 method.

Tolile Classification ofexposure to localwind-driven rain

SELECTION OF MATERIALS AND CONSTRUCTION TO RESIST WIND-DRIVEN RAIN

The following factors affect the resista nce of

b rickwor k walls to wind·driven rain. The order of the

listing does not indicate relative importance. Each

factormust also be considered in relation to otherfunct ions of the wall such as st rength, dura bility,

soundand thermal insulation:

• type of brick

• mortar composition

• thicknessof leaf

• presenceof a cavity

• width of airspace within any cavity

• mortar jointprofile and finish

• presence, type and thickness of any cavityinsulation

• architectural features and local practice

• presence of applied external surface finishes

• quality of workmanship to be achieved on site

Detailed considerations

1 7'fpe of brick

Brick ty pes vary considerably in their physical

properties, bu t when specifying brickwork with

regard to resistance to wind-driven rain nodistinctionis made between them.

In a wall constructed of dense bricks, with low

water absorption characteristics (for example thoseof the Engineering Classes) , on ly a relatively sm all

quantity of water will be absorbed into the bricks.

The greater proportion of any rainwate r falling on to

the wall will run down its face and may be blown

into a nd th rough it via paths in the mortar joints,

particularly at the interfaces between the mortarand the bricks (see 6 below).

In contrast, in a wa ll of bricks havi ng relatively

high water absorption characteristics, such as manyhan dmade and stock bricks, much of the water

runningoverthe wall surface in conditionsof

ABSORBENT

the "OVERCOAT" effect

DENSE

the "RAINCOAT" effect

driving rain will be ab sorbed into the bricks . If the

duration of the rainfall is short this behaviour may

be conside red beneficial because it prevents mo st of

the water reaching the mortar joints. However,when the surface of the material approaches

saturation point water tendsto run more readily

down the surface and, as in wallsof dense units,

may penetrate via paths at the mortar joints. In

verysevereand prolonged conditions ofdriving rainwater may be abs orbed further into t he bricks and

eventually reach their inner surface, first as

dampness andthen asfree water. Generally rain

ceases long before such complete saturation andwater is evaporated from the wall by the drying

effect ofwindandairmovement.

These two modesof action are sometimes

referred to as the raincoat effect, inthe case ofdense, low absorption units, and the overcoat effect,in the case of high abso rption units . Solid wa lling

can ultim ately be pen etrated by prolonged

exposureto wind-driven rain regardless of the waterabsorption characteristics of the bricks .

Although water abso rpti on va ries greatly

between different bricks, this property has only a

relatively small influe nce on the resistance of the

finished wall to wind-driven rain. In persistentconditions ofwind-driven rainwaterwill penetratemasonry leafs th rough the mort ar joints regardless

of the brick type.

Nodifference is detectable between the rainresistance of brickwork built of the va rious forms of

brick unit, ie. so lid, frogged or perfo rated . There

havebeen anxieties expressed that walls built ofperforated bricks m ight be less resist an t to wind·

drive n rain tha n those built with solid or frogged

ones, bu t such fears are unfou nded.

A reporton UK experience in the use ofpe rforated bricks, BRE Digest 273 Perforated clay

bricks'S), points out th at mo st of them are mad e

with bodies of low water abs orbe ncy an d th at , with

regard to rain penetration, there is no evidence ofany significantdifference in performance betweensolid and perfo rated br icks with equivalent low

porosity bodies. It also comments that there is noevide nce to support the suggestion that

perforations may act as reservoirs in whichrainwa te r collects dunng rainy pe riods,

subsequently giving rise to problems such as

efflorescenceor frost attack.

2 M ortar composition

Mortars vary in water permeability relative to

their cem ent content, high strength mortars of

Designation ( i ) and ( ii It e.g. 1:0-1J.. a nd 1:'4 : 41/;

ceme nt : lime: sand respectively, being the least

permeabl e. These mortar Designations are often

used in conjunctio n with dense, low water

abso rption fired clay bricks. This combination is

satisfacto ry but should not be regarded as providing

a waterproof. or near waterproof, co nstruc tion (see

6 below).

. Strong dense Designation ( i ) mortar is not

suitable for use with calc ium silicate bricks and

se lection is governed by other facto rs such as

accom modati on of movem en t, durab ility and

stre ngth. Designation ( iii ) an d ( iv I mortars are

often mo re appropriate for these bricks, eg 1:1:6

and' :2:9 cement : lime: sand.

Foralternative mortar ty pes and mixes of

Designations (i) to (iv) see Table 15 of BS 5628 : Part

3. The ta ble lists various mixes for ceme nt, lime and

sa nd mortars, masonry ceme nt and sa nd mortars,

and mortars of ceme nt and sa nd with the addition

of air-entra ining addi tives.

Of the various mixes specified for the mortars of

each Designation those incorporating lime in th eir

composi tion show a n improvement in bond

development and, as a consequ ence, a bett er

resistance to rain penetration th an those morta rs

based on air entrainme nt a nd/or mineral materials

other than lime. Howeve r, although this advantage

is detectable, it is not significa nt enough to justify

limiting the application of any particular type of mix.

3 Thickness of leaf

Solid wall construction of brickwork, in commo n

with ot her forms of ma sonry, gets wet when

subjected to ra in and absorbs so me of the wa ter,

but when the rain sto ps it dries out again losing the

moisture to the air by eva poration, an action which

is often accelerated by wind.

The resista nce to rain penetration of a solid wall

is th erefore dependent upon its thickness a nd this is

reflected in tradit ional const ructlcn - th in walls are

used in very shelte red locations and th ick ones

where exposure is greate r. Table 2 shows the

recomm ended minimum thicknesses for both

rendered and unrendered solid wa lls for va rious

categories of expos ure.

Maximum recommended category ofexposure rsee "'bI' n

Thicknessof brickwork(mm)

90

2'5

328

440

Unrendered

(S£lMJn I}

not recommended _"-51

not recommended 61

2

Rendered

{saMJrl: 2}

2

3

3

Extemallyinsulated(SarAAT3)

3

3

3

3

ImperviousCladding(SElNOff 4/

4

4

4

4

NaTE 1: A notional cavity should be providedbetween the internal surface of the masonry andany intem al lining.

NaTE2: Rendering should comply with BS5262.

NarE 3: External insulation should have a TechnicalApproval for use on solid walls subjected toExposure Category 3.

NaTE4: Examples of typical impervious claddingsyste ms are noted in 9 below.

NaTE5: Walls of half-brick thickness are Widely usedfor domestic garages and garden stores, but theymay be penetrated by persistent driving rain.

NarE 6: Historically 215 mm thick unrendered brickwallsare commonly found performing satisfactorilyin z-sto rev houses in towns and cities in the UK.Such locations are generally very sheltered wherelocal spel1 indices are of 20 11m2 or less .

nib e 2: Minimum thickness ofsolid brickworkwalls, with and without rendering. to resist rain penetrationin variouscategories 01 exposure (Based onTable 11 inBS 5628:Part31

Typicalsectionofcavity wall

'I.e Typical sectionofcavityw all at opening

>c--l'> __

~-~. ... ) .-_. -. " -

For all practical purposes brickwork can beeffectively jointed with the mortars conventionallyused in traditional and modernconstruction, butthe jointsshould not be considered waterproof.

The brickto mortar interfaces in the wall are the

positions most vulnerable to rain penetration.A

microscopiclabyrinth of voids exists at the interfacebecause of the physical nature of mortar bonding.The interface is also a likely location for capillarycracks dueto imperfect adhesionbetweena mortarand bricks. Good adhesion is difficult to achievewith absolute consistency and the interfacemay bedegraded further by crackingdue to moisture andthermal movements subsequent to construction.

The toolinginvolved in finishing joints such asthose with bucket handled and struckweatheredprofiles firms the mortar, reducing its permeabilityat the surface, and pushes it tight to the bricks,thereby improving its adhesion to them. Both

characteristics improve thejoints' resistanceto

penetration by water.

Recessed joint

profiles form ledgeswhich impede therun-offof waterand

encourage it to enterthe walling at the

mortarI brick interfaces.Recessed joint profiles formed by rakingout themortarwithout subsequent tooling to firmitssurface further increases the vulnerability of thewall torain penetration. Recessed jointsalso reducethe width of the mortar joints. Compared withbucket handled and struck weathered profiles, therisk of rain penetration is greaterwith recessed

4 Cavity walls

Table 2 does not apply to cavity construction. Incavitywallsit is accepted that some water willinevitablypenetrate the outer leaf in prolongedperiods ofwind·driven rain, but proper designandpositioning ofdamp·proofcourses and trays and ofany insulation willminimisethe riskof penetration

further into the building. Where the cavity isunavoidably bridged, e.g. at window and dooropenings, correct detailing is essential.

Cavity wallswith a half-brick thickouter leaf(90mm minimum)can performacceptably in allcategories ofexposure listedin table 1. Nevertheless,a designer mayconsider theuseofa thicker outerleafto reduce the quantityofwaterreaching the cavity.

No reliance should be placedon the inner leafofa cavitywall to resist waterpenetration.

6 Mortar joint, profile and finish

Regardless of the type of brickor the mortarcomposition, it is essential to fill completelyallbedjoints andcross joints (sometimes referred toas"perps" or "perpends") to minimise the riskof rainpenetration. Workmanship isvery importantin thisregard , see 10 below.

5 Width of air space within any cavity

In cavity walls the space between the two leavesofmasonry is intended to prevent any water from

passing from the outerleaf to the innerone. In most

situations a cavitywallwith a half-brick thick outerleaf (90mm minimum), a SOmm cavity and an inner

leaf issatisfactory. In conditions ofmore severeexposure considerationshould begiven to theuseof wider cavities.

Mortar joint profiles

joints and so they should only be used in Sheltered

exposurecategory locationswhen resistance torainpenetration is important.

BucketHandle

StruckWeathered

Flush Recess ed

7 Cavity insulation

Thermal insulation materials may be effectivelyinstalled within the cavity of a cavity wall to

increase itsoverall resistance to thermaltra nsmittance, thereby reducing heat loss from the

building. But if the insulation is not installed

correctly, or without due care, its presencecan

constitute an increased risk of rain penetration of

the wall tsee Thermal insulation: avoidingrisk9' 11.

Some insulation materials arebuilt-in so that afree airspace is retained,Le. a partial'fill system. The

retained air space shouldbe a minimum targetwidth of 50 mm. Inner leafconstruction of faceinsulated blocks require a retained air space.

In a full·fill system the cavity space between the

innerand outer masonry leaves is filled

wit h insulation material either bybuilding it in asconstruction proceeds

or by injecting or blowing it into the

cavity after the wall has been

completed . The cavity space should be

a minimum target width of 50 mm, but

the riskof rainpenetrationwill be reduced if a

wider cavity isused,

Thermal insulation materials are provided in a

form specifically intended for a particular

insta llation method. Products for partial ·fill

applications shou ld not be used for full·fill ones, an d

vice versa. Only products specifically manufactu red

forinsulating masonrycavitywallsshould be used;

other forms of insulation material must neverbe

substituted. A summary of the types of materials

appropriate for use in partial-fill and full-fill cavity

wall insulation systems is given in Table 3.

Some thermal insulation materials, egoinjected

foamed urea forma ldehyde . are subject torestrictions of their use vis-a-vis severity of

exposure. All thermal insulation materials should be

specified and installed in acco rdance with the

relevant British Standa rds, Technical Approvals and

the manufacturer's instructions.

The inclusion of insulation materials in a cavity

wall sometimes requires the installation of

add itional cavity trays (see page 19).

_Intem.rbrick or block

Cavity wall withpartial-fillcavity insulation

Cavity wall withfull-fillcavity insulation

mble3 Thennal insulation materials for use in cavityinsulated walls

Product..... ; ..

Partial-Fill Cavity Insulatian

Mineralfibreslabs

Foamedglass slabs

Expanded polystyrenebead board

Extrudedexpanded polystyrene board ~

Rigid polyurethane (PUR) board

Polyisocyanurare (P1R) board

Futl-Fill CavityInsulation

UTTS to U 811U.TIN

Mineralfibre bolts

LOOSEMAnxtAL TOU .. toWN IN

Mineralfibre

Polystyrene beads

Polystyrene granules

tNT£CfU) FOAM£D nASf1C

Ureaformaldehyde (UF) foam

Polyurethane (PUR} foam

(/or stabilization and insulation

ofCavitywalls)

British Standard

3837 : Part 1 Specification

3837 : Port2 Specification

4841 ' Part , Specification

4841 : Part, Specification

6676 Part 1 Specification

6676 Part 2 Installation

5617 Specification

5618 Installation

7456 Instal/ation

7457 Sped{icotion

8 Architecturalfeaturesand lacalpractice

Architectural featureshavean important affectan the risk of rain penetraticn. Thedesigner shauldalwayscansider whether the destgn detailswillincrease the tendencyfor themasonry to be wettedmare than it wauIdbe by incident rainfall alone.

Examples of features thatcause concentratedwetting are:

a) Anarea of glazing or imperviouscladdingcanproduce a large amountof surface waterrun -off

andunless there is a gutter to collect it, oraprojecting sillto throw it clear, excessivewettingand possible waterpenetration canoccurin anymasanry below

b} Because of its profile a recessed bandcoursecancause local concentration of wetting.Corresponding intrusions intothe cavity duetothe setting back of bricksar ather masanry unitsto farm the feature may increase the riskof watercrossingthe cavity,Theuse of reducedwidthunitsto form the recesswould avoid intrusioninta the cavity Alternatively, the introductionofa cavity tray immediatelyabave the set-backmay be considered.

Thedegreeaf welting of masanry canbereduced by ensuring that rainwater is thrown clearof the walls by adequate averhangs and drips ar byproviding drainage to takewater away from the masonry,

Append ix E of BS8104 contains a deta iled

commentary on the protection afforded by

projecting features such as sills, copings, string

courses, roof eaves andverges. It explainswhysmall overhangsareso effective in protecting walls.

It might be anticipated that water

dripping from a projection would

quickly be blown onto the wall a short

distance below. However, airclose to

the wall forms an almost still boundary

layer and to the exte nt that it moves at

all, it flows parallel to the surface.

Because of this droplets falling from

projections tend to fall vertically down to

the ground .

In general the Appendix

corroborates the beneficial effects

tra ditionally asc ribed to projecting

features, but it also reports on studieswhichindicatethat in some conditionsof high winds anoverhang at the top of a wallcan lead to greater

welli ng when compared with a flush topped wall.

These findings are embodied in the allowances

relating to gable ends and eaves to pitched and flatroofs in the BS 8104 method for assessing exposure

to winddriven rain. The Appendix also reports on

the effect of surface texture and also theconcentration bywind of surface waterrun-offatexternal and internal corners of buildings.

The designer should always take account of

local knowledge, experience and the evidence of

local traditional forms of cons truction and building

detail. The fact that some building design features

are not characteristic of a particular area orregionmay indicate their unsuitability for the rigours of

local exposure.

Unsightly patchiness due to differences in wetness caused bythe application 01water repellent treatmentto brickwork at parapet level

9 Applied external surface finishes

Forboth smgle-leafand cavity walls, totalresistanceto rain penetration can be achieved onlyby the use of impervious cladding systems . lYpicallysuch systems are panels, boards or sheeting ofmetal, plastics or timber with weatherproof joints,

andoverlapping slates, shingles. or tiles.

As indicated in Table 2 rendering cansubstantially enhance the rain resistance ofbrickworkwalls. It may be applied to solid walls andto cavity walls. It is essential, however, to select theright type of mortar mix , the thickness and number

of coats and to deta il the wall correctly in order tominimise shrinkage cracking, which mayotherwisereduce the effectiveness of the rendering. Therecommendations of BS 5262 British Standard

Code ofpractice for external rendered finisheiJ6}

and BCA publication Appearance matters - 2 :External rendering71should be followed .

The combination of full-fill insulation andrendering inhibitsthe drying out of any moisturethat may enter the outer leaf of masonry. Themoisture contentof the outerleafmayconsequentlyrise increasing the risks of frost action of themaso nry and sulfate attack of the jointing andrendering mortars. Claybricks of durabilitydesignations ML or MN las specified in BS 3921British Standard Specification for Clay brickiJ 8I1

arenot recommended for such wallsin locationsexposed to Severe orVery Severe categories ofexposure to wind-driven rain. FL or FN claybricksmay be used.

In allcategories of exposurewhereFN orMNclay bricks are to be used behind rendering thejointingand render undercoat mortars should bemade with Sulfate Resisting Portland Cement ISRPCI.

The use of masonry paint systems (see BS 6150British Standard Code ofpractice for painting of

buildingiJ911 and other proprietary external finishesincluding colourless treatments, e.g. silicone-basedwater repellents (see BS 6477 British Standard

Specification for water repellents for masonrysurfaceg.10Il, may increasethe resistance to rainpenetration. However. they may also reduce the rateof evaporation of any water from the wall and so the

moisture contentof the wallcan increase ifwatergets behind the paint orsurface treatment eitherbypenetrating imperfections in it orentering fromadjoiningconstruction. In some cases this has leadto localisedwaterpenetration and/or saturationofthe brickworksufftcient to cause frost damage toclay bricks of ML and MN durability designation inwinter conditions.

Water repellent surface treatments arenotgenerally recommended for clay brickwork.Traditionally brickwork that is correctly specifiedand constructed is durable, withstands weatheringand resists the penetration of wind-driven rainwithout the needofwaterrepellent treatments.They should not be applied to clay brickworkwithout the approval of the manufacturer of thebricks specified.

10 Quality of workmanship to be achieved on

site

The qualityof workmanship actually achieved,both when constructing masonry andwheninstalling any insulation material, is the mostimportant factor affecting resistance to rainpenetration, All workmanship should be inaccordance with BS 8000 : Part 3 British Standardfor workmanship on building sites : Codeofpractice for masonry" l. Detailedguidance onworkmanship is also given in BOA Building Note 1Brickwork " Good site practice ' ' I.

Some brickwork requires particularcare initsconstruction compared with others. For example,considerclay bricks of low waterabsorption andthose of high water absorption. It has been statedthat allmortar joints should alwaysbe filled(see6above), but from the description of the raincoateffectand the overcoateffect (see 1above) it will beevident that minor imperfectionsin the jointing of

high water absorption bricks (overcoat effect) willnot alwaysbe critical. This is because. except in

"'Tipping andtailing" generally produces crossjoints with poorreslst ance te fain penetration

severe and Very Severecategories of exposure,most

periods ofwind-driven rain are interrupted bya

drying period beforethe bricks in the wall havebecome so saturated that the rain passes through .Bycontrastrain falling on a wallof low waterabsorption bricks(raincoat effect) will run downovertheirglass-like surfaces to enter immediatelyany imperfections in the jointing.

The importance of filling allmortar joints toensuregood resistance to rain penetration cannotbe overstated, but the cross-joints ("perps") are oftennot filled properly because they are formed using apoortechnique known as "tipping and tailing".Smalldabs of mortar are Wiped on the leading andtrailing edges of the end ofeachbrickwhen laying. This badpractice leads to cross-jointsthat are not adequately filledand therefore do not have thebest resistance to rainpenetration. Any anticipationthat the joints willsubsequently befilled by mortar flowing down into themfrom the next layer of bedding mortar is fallacious.Filling cross-joints by this means is impossible.Stretcherbonded walls have sixty cross-joints persquare metre and so if they are poorly filled theshortcoming can be significant. Filling cross-jointsproperly by applyinga fulllayer of mortar to theend ofeach brick is not difficult or time consuming.It is regarded as good practice and therefore it is notunreasonableto insist that it is done.

-Buttering- the endofa brickwithmortargives 8 fully filled cross joint

DAMP PROOF COURSES AND CAVITY TRAYS

Genera l

Adamp-proof course(dpc) in a building isintendedto provide a barrierto the passageofwater from the exterior of the building to theinterior, or from theground to thestructure, or fromone part of the structure to another.

Where the dpc is intendedto prevent theupward movement ofwater due to capillary actionthroughmasonrymaterials continuity is importantalthough, in normal circumstances, no hydrostaticpressureis involved. loints shouldbe made inaccordance with the instructions ofthemanufacturer of the dpc material used. Where nospecific instructions are given, the dpc shouldbelappeda minimum 100mm orthewidth ofthemasonry leafat comersorintersections. Penetrationofdpc's and cavitytrays by services, reinforcement,fixings, etc. shouldbe avoided as faras possible.Where they haveto pass throughcareshouldbetaken to form the necessary holeneatly andcarefully seal around the breach.

Where water is subjected to hydrostaticpressure, or ismoving ina downwards directionunder the Influence ofgravity, any jointsInthe dpcshouldbe madewaterproof by lapping and sealingfollowing the dpc manufacturer's specification forsealantor adhesive.

Opc's shouldextend throughthe full thicknessofa wall or leaf, and to the externalface whereitshouldbe clearly visible. Adpc shouldnot bebridged by pointing, rendering, plastering, walltiling, etc. To prevent penetrationofwater beneaththe dpc,whichcan occurIfit Isplaced directly on anirregular bed surface, and to producea goodbondto resistsubsequentmovement, dpc's shouldbelaid on a smoothbed offresh mortar. The use ofcoarseaggregates for the mortar shouldbe avoidedas they mightdamage the dpc. Sometimes dpc's areInstalled to form a slipplane to accommodatedifferential sliding movements betweenadjacentparts of the building structure; Insuch a case themortarbed shouldbe trowelled smooth, allowed toset, and then cleaned offbefore the dpc is laid.Alternatively, a doublelayerofappropriate sheetdpc materialwith no mortar or adhesive betweenthem may be specified.

itoove Ope's should be sandwiched betwee n mortar

Performance

To ensure adequate performance, dpc's andcavitytraysshould havethe following materialproperties:

(a) an expectedlife at least equal to that of thebuilding

(b) resistance to compression without extrusion(c) resistance to sliding wherenecessary(d) adhesionto units and mortarwherenecessary(e) resistanceto accidental damageduring

Installation and subsequent building operations10 workability at temperaturesnormally

encountered duringbuildingoperations, withparticular regard to forming and sealing joints,fabricating junctions, steps and stop ends, andthe ability to retainshape

table 4 gives Information on performance ofIndividual materialscurrently used fordpc's.

BSB215 BritishStandardCode of practicefordes/gn and installation of damp-proofcoursesin masonry construction " )gives guidance on thebasicprinciples concerning dpc's, their function andtheir Installation Inmasonry. Itcontainsrecommendations for the selection, designandInstallation ofdpc's Inboth solid and cavityconstruction.

Material

Rigid Materials

Resistant to extrusion :

..... ~~~~'.~iii~l~ .ad

Ease ofiointing

..:.

Limitationsor benefitsin use

OAr DI'C MICKS

complying with as3921

SLAncomptying with as 743

Semi-Rigid Materials

MASTIC AsnlALT Xcomplying with85 6925 or6577

..... .. . .. :... .

Flexible Materials

UADSH£ET

comptyingwith as 1178

COP1'EJt SHEET

compTying with C 104 orC 106ofBS2870

.t SUitable against rising moisture onlyGoodperformance in resisting flexural stress.

.t Suitableagainst riSing moisture only.

nf a

......; .

Requires protective coatingagainstcorrosion when setIn mortor > 25mm.

Requires protective coatingto avoIdstaining masonry.

MTUMENSHEET

compTying withas 6398- withHessian base(class A)

- withFibre base(class B). wtth Hessian base andlead (Class DJ. withFibre baseand lead(class E)

LOW DENSlTF 1'OLrETHnENI!SHEET

complying withas6515

rrTCH I"OLYMElI SHUT

~

~

~

~

'"

Difficult to handleIn coldweatherDifftcultto handlein coldweather.Di/flcultto handleIncoldweatherDifftcultto handleIncoldweather

Poorbond performance. Norrecommendedtor use In conditions offlexural stress.

Goodbondingperformance with mortar.

laDle 4 Summaryof materialsused for damp proof courses and cavity trays

Junct ions

Dpc and cavity tray detailscan be simple andstraightforward in straight plainwalls, but atcorners, junctions, returns, curves, changes inlevel,changes in plane,around openings, etc., the needforcontinuity oftenrequires quite complicatedinstallation of dpc material. During the preparationofdetail design and specification for a buildingcareful consideration should be given to thesepositions and detailedthree-dtmenstonal drawingsmade ofalldpc's and trays at junctions, steps,angles and stop ends. Many common detailscannotbe formed satisfactorily In-situ, unless they arefabricated in lead. If materialsother than lead are tobe used in complex situations, then pre-formedcloaks shouldbe specified, so as to restrict the siteoperation to simple jointing.

Continuity and support

Where practicable, dpc's and cavitytraysshouldbe formed Ina continuouslength of material tominimise the need for joints.Cavity trays should besupportedat their joint positions to facilitateeffective sealing. Continuous support isadvantageous as it avoids sagging and deformation.

Resisting rising damp

Immediately abovegroundlevel

In everyexternalwall, a dpc shouldbe providedat least 150 mm abovethe finished level of theexternal groundor paving. To preventthe transferofmoisture from external wallsintosolidfloors, thedamp'proofmembrane in the floor, and the dpc inthe wall, should overlap a minimum of 100 mm orbe sealed. In cavity workthe cavity should be filledto ground levelwith fine concrete, and weepholesshould be left In the vertical cross jointsof the outerleaf, at intervals not greater than 1 m, immediatelyabovethe top ofthis fill. The purpose of the fill is toprevent the leaves of the cavity wall beingdisplacedinto the cavity by pressurefrom the groundduringbackfill operationsorsubsequent loading ofthe ground.

Belowgroundlevel

Horizontal and vertical dpc's are required wherethe lowestfloor of the buildings is belowgroundlevel. Inthis situation it may be necessarytoconsidertanking (seeas 8102Bridsh Standard

Code ofpracdce for protection of structures

against water from the groun d 14)).

--­_ ... .....,."-'r'._­.--

Stop ends fmedtodiscontinuouscavity tray

Pre-formed cavity tray for anarch

Controlling downword movement ofwoter

Cavity walls

The design and specification of a cavity wall

should be based on the assumption that, inconditionsof persistent driving rain, water willpenetrate theouterleaf andrun down itsinnersurface within the cavity, Wherethe cavity isbridged, egoby lintels, structural beams, floor slabs,pipes, and ducts, dpc's in the form of cavity trays,with stop ends and weepholes, should be provided

to divert water out again.

Over openings

Incavity walls, cavity trays should be providedoverall openings(including small openings for

ducts, services, etc), unless they arewell protectedby a roofor balcony overhang.

The cavity tray should step down or slopeacross the cavity not less than 150 mm towards theexternal leaf and, preferably, terminate in a smalldrip on the faceof the wall.

The cavity tray overan opening should overlapthe vertical dpc's at the jambs to ensure continuity

of damp'proof measures (see figure on page' 8)

Arches

The curved form of an arch makes the use of anormal cavity tray impossible. A conventional cavitytray can be installed in the bed joint immediatelyabove the crown of an arch and for a minorsegmental arch in a relativelysheltered location this

may be considered acceptable. The tray shouldextend beyond the width of the arch and be filled

with stop ends. To improvethe construction short

lengths of flexible sheet dpc material can beset aroundthe curveof the arch in an overlapping arrangement.

A simpler and more reliable construction is to

use a pre-formed arch tray (see figure above).Depending on the detail design of the opening thetray may be installed at the intradosor the extrados,

i.e. under or over the arch ring.

Apre-formed tray should incorporate stop endsand, becausethe

arch form inevitablydrains any

penetratingwater to

itsbearings, care

should be taken toensure effective

weepholesare

provided.

Weepholes

Weepholes are required in the outer leafimmediately aboveany cavity tray so that watercollected on the traycan be diverted out to the exteriorof the building. They should be formed in verticalcross joints at intervals not greater than 1m. Thereshouldbe not lessthan two weepholes over eachopening.

It is usual to form weepholes by leaving anominal 10 mm wide cross jointunmortared.Theheightof the weephole is generallydetermined bythe height of the brickbut it is not critical. It shouldbe large enough to avoid any tendency to becomeblocked by debris. Weepholes formed betweensoldierbricks may be full height, but need only beabout 40 mm.

In tallbuildings subjected to harsh exposurethere has beenexperienceof rainpenetration duetohigh winds blowing into cavity wallsthroughweepholes and moving water up beyondtheupstand of dpc trays. Proprietarydevices areavailable to assist the formation ofweepholes thatallow water to drain from the cavitybut restrict theingressofwind andl or rain.

In this building there is a cavitytray inthefifth course above thesoldier course. Note theweepholesatthislevel- open crossjointsat900mm intervals

'Right Aproprietaryplastic windbaffleinsert toform aweephole

Stopends

Wheretrays arediscontinuous, andin a positionthat is not wellprotected by a roofor balconyoverhang, stop ends should be filledat or near theends of the tray, generallycorresponding to cross

joints in the brickwork. Theyshould be bonded to the trayto givea waterproofseal.Stopends prevent the possibility ofwater in thecavity runningdown onto the tray and beingthrown offits ends into thecavity · at the jamb ofan

openingsuch a concentrated flow ofwatercouldrun behind the verticaldpc in that part of thewalling, wet the inner leaf and lead to dampness ofthe internal faceof the wall. Stopends areparticularly desirablewhen cavityinsulation isinstalled.

Steel lintels are availablewhich are shaped andfinished to act as a cavity tray without the additionofsheet dpc material.These lintels also require stopends to be filled.

_ Tray ove, lintel ­note stop ends

_ Vertical dpc wherecavity closed at jamb

Lapping of vertical dpcat jambs toopenings in cavrty wall

Arrangement ofvertical dpcand insulalion atjambs to openings in a cavity wall

Requirements for damp proof courses andcavity trays for specific parts of buildings

At jambs of openings

Where a cavity wall is closed at the jambs of

openings by masonry, a vertical dpc should be

inserted to prevent moisture passing fromtheouter

leaf to the inner parts of the wall. The vertical dpc

should extend into the cavity at least 25

mm beyond the width of the closer and

any cavity tray above should extend

beyond it tsee figure above). Insulation

material may also be placed in this

position to minimize cold bridging.

Proprietary closers are ava ilable which

combine the functionsof closingthe

cavityat the jamb, preventingmoisture

transfer, stabilizing the masonry leaves, reducing

cold bridging and providing fixingfor window or

door frames. If these areused followmanufacturer's

instructionsfor installation and linking with

assoc iated dpc's at the head and sill.

A frame in an opening should be located an d

fixed in such a manner that transmissionof water

past the vertical dpc is avoided . Where the frame is

to be built in, the dpc should be secured to the

frame first. If the frame is to be fixed later, the dpc

should be left projecting within the opening. Vertical

dpc's at openings shou ld be positioned to overlap

any horizontal dpc at the sill of the opening and be

overlapped by any cavity tray at the head [see

figure above).

A proprietary plastic cavitycloser I frame fixing

Sills

All pervious or jointed sills, or sub-sills, shou ld

be provided with a dpc for the full length and width

of the sill bed. The dpc should be overlapped by the

vertical dpc's at the jambs of the openings [see

figure on page 18). Where the sill is in contact with

the inner leaf, the dpc should be turned up at the

back and ends for the fulldepth of the sill(see figure

on page 8).

Requirements for additional cavity trays withcavity insulation

When cavity insulation is present but not

installed throughout the fullvertical height of the

cavity (eg. stopped at eaves level in gable ends) a

cavity tray is required immediately above the

insulation to protect from the hazard of mortar

droppings or other debris forming a bridging of the

cavity on the top of the insulation .

In buildings over 12 m high, with insulated

cavity walls, cavity trays are required to subdivide

the cavity so as to avoid surcharge by water that

may penetrate the outer leaf of masonry. They

should be insta lled at a maximum of 12 m above

ground level and at a maximum spacing of 7 m

thereafter. In framed building with brickwork

cladding the trays required to subdivide the cavity

can be the same as those associated with the

cladding support system .

In both these cases trays should step down aminimum of 150 mm towards the outer leaf and

weepholes should be provided at intervals not

greater than 1 m.

Addrtional cavity tray 10protecttop of cavityinsulation

Additional cavity trays to subdividetall walls with cavity insulation

Detail of parapet showingdpc tray

External wall becomingan internal wall

If, in its height,an externalwallbecomes aninternal wall at lower level, as inthe case of a roofabutting a wall (e.g. ina stepped terraceofhouses,ora porch, garage orconservatory annex)a cavitytray shouldbe installed to drainthe cavity abovethe level of the lower roof.

Ahorizontal abutment requires a level cavitytray withstop ends and weepholes. When a pitchedroofabuts such a wall, a cavitytray stepped tocorrespond with the slopewill be required;alternatively a system ofoverlapping preformedtraysmay be installed to collect and dischargewater from the cavity. Ineithercase stop ends andweepholes are essential.

Proprietary systemsexist forthese applications.

Parapets

Ina solid parapet wall a dpc shouldbe providedat a heightofnot less than 150 mm above the topsurface of an abutting roofsystem and lap overtheflashing to the roofing to givecontinuity,

In a cavity parapet wall a cavity tray shouldbeinstalled to provide the same function. It shouldstep at least 150 mm within the cavity. When cavityfill insulation is installed the tray shouldstep downto the outer leaf(away from the roof]. When there isno cavityinsulation the designer should considercarefully which way to step the tray inany givencase. It is safer to directwater towards the outerface (away from the roof]. Concern that thismaycause staining on the face of the wall belowisexaggerated. Ifslopedinwards (towards the roof)experience showsthat there is a danger in thatrainwater may be driven below the tray and trackalong its underside and so gain accessto the innerleafof the wall, the underside ofthe roofcoveringand the interior of the building.

Itshouldbe noted that dpcs and cavitytraysimpairthe structural integrity of the parapet andthe wall beneath and also the coping above. Opcmaterialswithgoodbonding performanceshouldbe specified.

stability of the assembly the dpc can be placed in abeddi ng two or three courses below the topmost

one . All materials above the dpc must be frost

resistant. In cavity walls flexible dpc's requiresupport overthe cavity to avoid sagging anddeformation and to facilitate effective sealing oflapped joints.

Resistanceto waterpenetrationshould notprejudice provision formasonrymovement.Movement control joints in the masonryshouldbecarried th rough any coping or capping and sea lant

applied as in the corresponding joint in the wall below.

Consideration sho uld be given to copings and

cap pings being displaced by lateral loads, and to

the possibility of vandalism. L-sha ped copings and

clip-over copingsmay be more satisfactory insomesituations. Where necessary, copings should be

SUitably fixed down and may be doweled or joggle­

jointed together. Copings and cappings to the

sloping tops of gable end walls present particular

problems of sta bility and security. They require

careful consideration of the practicality of construction.

Brickwork withflush capp ings canbe very successful.butrequires extracare inthe selectionof materials for durabili ~

tv. anundemanding oftheirweathering characteristics. andofthe implicationsofdesignfeatures onweathering

Copings and coppings

A coping is a construction that protects the topof a wall and sheds rainwater clear of the vertical

wall surfaces below, generally by having a

weathered top surface and a throa ted overhang to

one orbothedges. Acappingis a construction atthe top of a wall, but it does not shed rainwater

clear of the wall surfaces below. Cappings are

generally flush, but they may have featu res which,

althoug h they overhang the surface of the wallbelow, do not adequately protect it by throwing

water clear.The traditiona l detailof bricks set on­

edge with tile creasing below sho uld be regarded as

a cappi ng rather than a coping.

Preferably parapet walls, chimney terminals,

freesta nding walls and retaining walls shou ld be

provided with copings. The drip edge of a throating

should be POSitioned a minimum of 40mm from the

face of the wall it is intended to protect. Where for

aesthetic orotherreasons a cappingis used specialcare is needed in the choice of materials fordurability, both for the capping itself and for the

walling beneath.

Where the capping or coping is [ointed, a

continuous sheet dpc should be provided in the

bedding mortarjoint.To increase the weight andCopings givepositive protection againstwetting ofwallingbelow

Chimneys

Chimneys may be built in solid or cavity wall

construction. Wherea chimney stack isincorporated in an outer cavity wall, preferably the

outerleafand cavityshouldbe continuous aroundthe chimney stack for the full height of the outer

walland then completely surround the chimney

stac k whe re is projects above the roof. Corbelling

from the chimney breast may be necessary below

the roof line, to support the outer leaf at the sides

and back of the chimney stack.

If the chimneyis set inan internal partition orparty wall and the roof is steeply pitched, a

reasonable height of chimney willbe exposed in the

roof void and any dampness in the masonry willbe

able to dryout ina ventilated roofspace. However,with a low pitched roof, when a chimney is located

at the eaves, or the roofspace accommodateshabitable rooms this beneficial effect will not apply

and particular carein the design and constructionof the roof/chim ney intersection wtllbe necessaryto prevent moisture penetrating into the masonry

below.

Opc trays should be provided to prevent the

downward passageof water. Horizontal traysshou ld extend through the thickness of the chimney

wall and into the flue liner,with an upturn at the

inner face of the flue. Externa lly it should be linked

with any flashing at the intersection of the chimney

with the roof. The figure below illustrates typical

arrangements.

It should be noted that a sheet dpc at the point

of intersection with the roofreduces the structuralintegrity of the masonry, and the stability of the

chimney stack and its resistance to lateral windloading needs to be considered. Chimney stacksbuilt in cavity work may be provided with a dpc tray

of a materialstiffenough to form a cavity tray

without beingbuilt into the inner leaf and this

provides structural continuity.

A horizonta l dpc should always be provided

below any coping or capping at the top of the stack

unless it is a jointless, waterresistant material, egoaone-piece dense terracotta, slate orreconstructedstone unit, or a sheet metal assembly in one-pieceor with waterproof joints.

Structuralframes

Masonry supported by a structural frame,

requires particular attention to be paid to thedetai ling of trays and dpc's to ensure their

continuity. Where cavity brickwork is supported on

an edge beam, or floor slab, a cavity tray with a

minimum upstand of 150 mm should be provided

to prevent moisture penetration into the structure.The cavity trayshould be continuous around anycolumn, or other structural member, that obstructsthe cavity. When a structural memb er bridges the

cavity, a vertical dpc should be included between

the structural member and the external leaf, andstop ends fitted to any ad jacent cavity trays.

Where complex shapes are needed,

prefabricated cloaks should be considered to

minimise difficulties of construction.

£eft Opc trays andflashings in masonrychimneyat roof penetration

Flashings and weatherings

The material to be used should be sufficiently

malleable to perm it dressing into shape, but

sufficiently stiff to maintain its shapeand to resist

lifting by the wind. Metal flashings other tha n lead

should, preferably, be pre' formed.

Flashings sho uld be bedded into the work a

minimum of 25 mm, and be provided with welted ,

orotherwise sealed, joints, oradequate overlaps.

Mostexternal wallsareexpectedto prevent rainpenetrating to the interior of buildings .

In masonrycavity walls it is acceptedthatsome water will pass thro ugh the outer leaf in

prolonged periods of wind·driven rain, but the

design of the wall is intended to dea l with this

inevitable eventuality. The risk of furthe r penetration

throug h the wall and into the building is minimized

by the proper des ign and installation of the wall's

associated damp-proof systems.

Environmental and ecanomic benefits have led

to the incorporation of various types of thermal

1. Building Research Establishment. Repo rt DrivingRain Index (1976)

2. BS8104: 1992. British Standard Code of practicefor Assessing exposure ofwalls to wind-driven rain.

3. BREReport BR 262 : 1994. Thermal insulation:avoiding risks.

4. B55628: Part 3: 1985. British Standard Code ofpractice for the use of masonry: Materials andcomponents,designandworkmanship.

5. BRE Digest 273 : 1983. Perforated clay bricks

6. B55262: 1991. British Standard Code of practicefor external rendered finishes.

7 . British Cement Association publicationno.47.1 02. Appearance matters -2: Externalrendering (1992) W Monks

8. BS 392 1: 1985. British Standard Specification forClay bricks.

The designer shouldconsiderhow flashings aretobe fixed and at what stage in the constructionprogramme to provide secu re fixing and avoid

damage to dpc's. The materials should be selected

with due regard to the likelihood of corrosion and

given protective treatment asnecessary.

To avoidstaining of masonryfrom the run-off ofrainwater, consideration should begiven to theneed for surface treatment of somemetals.

CONCLUSION

insulationmaterials into modern cavity walls.

Effectiveinstallation met hods have been deve loped

to ensure that this isdonewithout impairing the

wall's performance in bad weather.

The incidence of wind and rain experienced inthe United Kingdom can be very testing, but walls

with facing brickwork can efficiently meet the

cha llenge. With care and attention to design and

workmanship, stra ightforward and well established

construction methods can provide wallsthat areresistant to rain penetration and also attractive,durable and economical.

REFERENCES

9. B5 6150: 1991. British Stan dard Code of practicefor painting of buildings .

10. B56477: 1992. British Standard Specification forwaterrepellents for masonrysurfaces.

11. B58000 : Part 3: 1989. British Standard forworkma nship on building sites : Code of practicefor masonry.

12. Brick Development Association Building Note 1. .Brickwork· Good Site Practice. (1991)TLKnight

13. B58215: 1991. British Standard Code of practicefor design and installation of damp-proofcoursesinmasonryconstruction.

14. BS8102: 1990. British Standard Code of practicefor protection of structures against waterfromthe ground.

ISBNo 900191 OS 8

ACKNOWLEDGEMENTS

All photography by Brick Development Association except as follows:

Frankwalter - covers,p.u upper. p.21 lower

Cover & p.1IglI :z 1: Houses at Victoria Park. Virginia Water, Surrey

....rchitects: The Howell Smith Partnership

Page 4: CascadesHotel and flats, Isle of Dogs, London E14

Architects: ClWG

Page 11 upp er : Flats& maisonettes, Hadrian Estate,Hackney. London E2Architects: LevittBernstein Associates li d

Page 11 lower: CompassPomt HouSing. Isleof Dogs. LDndon E14

Archuects: ~~mVD~on

Page 21 upper: HartlepooJeve Centre, develand

Architects: TheCulpm Partnership

Allenquir ies should be addressed to the autho r at the Brick Development Assoc iation.

The contents of this pubhcatmnare intended for generalguidance onlyand any person intendmgto use these contents for the purpose ofdesign. constructionorrepairof bnckworkor any related prcject should firstconsult a Professional Adviser.

TheBrick Development Association. Itsservants. and any persons who contributed to or who were In any way connected With this publicationaccept no babihtyarising fromnegligence or otherwisehowsoevercaused for any inluryor damage to any person or property as a result ofany use or reliance on any method,

product. instruction. idea,or other contents of this publication.