Openings in Masonry Walls - Blackwell · PDF file5 Openings in Masonry Walls ... 128...

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BY019-05 BY019-Fleming-v6.cls September 17, 2004 10:55

5 Openings in Masonry Walls

For small pipes and cables 126For larger pipes and ventilators 127Large openings in masonry walls 127Alternative sill arrangements 136

Threshold arrangements 137Partitions of masonry 139Openings in timber frame walls 141

As we did with floors, we can classify open-ings in walls roughly by the size of openingrequired.

So we will look at:

� Openings for small pipes and cables<50 mm diameter

� Openings for pipes and ventilators >50 mmdiameter but <225 mm

� Openings in excess of 225 mm – large open-ings.

For small pipes and cables

Openings for small pipes and cables can nowbe drilled with a power tool fitted with an ap-propriate drill bit – solid for holes up to about50 mm and a core bit for larger holes up toabout 150 mm diameter. There are even somespecialised forms of bit which can cut largediameter holes but they generally require wa-ter cooling. All that is required is a power-ful enough tool, core bits requiring the greaterpower.

Because of the extensive use of cavities,sleeves must be built in across the full widthof the wall to prevent the leakage of pipe con-tents into the cavity and to prevent vermingetting into the cavity. Typical examples ofdrill bits and a sleeve in a masonry cavity wallare shown in Figure 5.1.

Sleeves should be built in with a slope downand towards the outer face of the wall to pre-vent water running through the sleeve. Thisdoes not need to be excessive – the sketchesexaggerate the slope.

Sleeves can be made of any solid drawnpipe material with a bore which will allow aneasy fit for the service pipe or cable passingthrough. Typically, copper piping or plasticspiping can be used. Ferrous material shouldbe avoided, as should aluminium which cor-rodes in contact with a strong alkali. Plasticspipe does seem to be the favoured choice onbuilding sites one visits, but it is uncertainwhether or not compatibility with cable in-sulation etc. has been considered in the choiceof pipe material.

Joints of the service pipes and cables are notallowed in the sleeve. With soft-walled pipesand cables, the ends of the sleeve should berounded or be fitted with some form of cush-ioning to prevent wear on the pipe or cable.Chapter 4, Timber Upper Floors, gives a de-scription of ‘cover plates’ where small pipesetc. pass through a floor. These can be usedwith holes in walls.

If the space between the sleeve and the pipeor cable is to be sealed, this should be donewith a non-setting mastic or sealer. Take careto ensure that it is compatible with the mater-ial of both sleeve and service pipe or cable.The space should be left large enough to make

126

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Openings in Masonry Walls 127

Masonry drill upto 50 diameter

Tungsten carbide(TC) tip on drill

Hole to allow dust toescape while drilling

Core drill -- 50 to

150 in diameter

Sleeve in masonry wall

Plastics ormetal sleeve

Service pipeor cable

TC teethset in

edge ofsteel ‘cup’

Steel cup withteeth cuts outa concentric

groove, leavingbehind a corewhich can bebroken off to

allow a further cut to be made until the hole

breaks through the masonry

NO joints in supplypipe or cable withinthe sleeve

Fig. 5.1 Drills for drilling through walls.

it easy to inject the mastic. The whole spacefrom end to end is never sealed, only about25 mm at each end.

For larger pipes and ventilators

The only large pipes to pass through domesticwalls are generally soil pipes or flue pipes –occasionally air extract ducts. In both casesthe norm is to cut a hole in existing walls orbuild in the pipe or flue with mortar, fittingthe masonry units around them. The cuttingis done with a hammer and chisel or a coredrill in a power tool. The latter causes muchless damage to the new masonry.

In the case of a flue, the heat generated maybe sufficient to damage cavity insulation. Insuch a case an approved sleeve (metallic orasbestos cement pipe) with proper clearancesmust be built into the wall. Manufacturers’literature should give the necessary adviceon the type of material to use for a sleeveand the clearances required, together with the

expected temperatures with various fuels forwhich the flue is suitable.

For pipes, ducts and flues up to 150 mmdiameter, holes would be formed or drilledto coincide with a junction of two bricks orblocks so that these units can be saved overrather than use a separate lintel, as shownin Figure 5.2. Also shown is a ventilator(not an airbrick) which generally tends to berectangular in section and made in brick coor-dinating sizes. For ventilators up to one brickwide therefore, there is no need to do anythingother than ensure that two bricks in every halfbrick thickness are evenly distributed overthe ventilator opening. Saving over relies onthe self arching effect of masonry.

Large openings in masonry walls

Large openings are made for doors, windows,hatches and the like. What differentiates themfrom previous openings is the need to pro-vide extra support over the opening as the self

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128 Construction Technology

Ventilator

Sheet metal orplastics duct

These three brickssave over

Flue liner in here

Flue pipe inhere

These three brickssave over the opening

Lineroutline

Void if a flue is used

LinerCover plate on flueliner over void

Fig. 5.2 Saving over in brickwork at ducts, pipes and ventilators.

arching effect can only be partially successful.Support is provided by lintels.

Lintels can be made from a wide variety ofmaterials and a variety of shapes. Materials in-clude stone, reinforced precast concrete, pre-stressed concrete, cold rolled mild or stainlesssteel sections, and hot rolled mild steel sec-tions. Old buildings may have timber lintels or‘safes’ but these are no longer used and shouldalways be replaced during any refurbishmentwork. Shape will be discussed as we look ateach application.

There is some terminology to learn. Anylarge opening has:

� A bottom – the sill for windows or thresholdfor doors

� A top – the head which has a soffit or soffite� Two sides – the jambs which have reveals.

Once a frame is put into the opening, the soffitis divided into an inner and outer soffit, the re-veals are divided into inner and outer ingoes,and the sill into inner and outer sills. Theseare all illustrated in Figure 5.3.

Cavity walls have the cavity closed at thehead, jambs and sill or threshold. A fur-ther feature is the positioning of the door or

window frame within the opening. Wherethere is a risk of wind-driven rain, the frameis positioned back in the wall thickness, thusgiving shelter to the joint between frame andwall. This situation arises generally in Scot-land and in northern and western and south-western England, Wales and Northern Ire-land. In more sheltered areas, such as theHome Counties, Norfolk and Lincolnshire,the frame was traditionally placed flush withthe outside face of the wall, and the majority oftextbooks showed frames in this position. Thesituation has changed somewhat and the text-books now tend to show the frames set backbehind the face of the wall. Setting framesflush with the outer face of the wall had im-plications for making a weatherproof joint be-tween frame and wall which did not rely onsome form of mastic. Like flattery, mastic is thelast resort of the rogue builder in situationslike that. Mastic is advocated in the detailswhich follow but it is not relied on entirely;the detail itself has to be correct first.

Another area for concern was the closingof the cavity at head, jambs and sill. With theframe so far forward of the cavity, closure washaphazard in practice and the positioning of

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OU

TS

IDE

OUTSIDE

Frame

Outer ingo

Inner ingo

Inner sill

Inner soffitOutersoffit

Outersill

Soffit

Reveal

Sill

Jamb

Threshold

JambsSill

Jamb

Head Head

Fig. 5.3 Terminology associated with openings inwalls.

the DPC at jambs and head was never quitesatisfactory.

This chapter will deal with frames set backfrom the face of the wall – indeed the outerface of the frame should align with the innerface of the outer leaf of masonry in a cavityor timber frame wall construction. The detailsshown all work, and work well. They functionin the most extreme weather conditions in theUK.

Closure of cavities was traditionally, pre1970, done by:

� Making inner lintels wide enough at thehead with a DPC at the closure

� Making sills or thresholds wide enough,with a DPC at the closure

12--15 plaster

PCC innerlintel

Arris on plasterreinforced

15 quadrant bead

Window headTimber inner sill

Timber grounds

Bedmould

DPC behindmasonry sill

20 roughcast ordry dash finish

PCC outer sill with handling steel

Stooled end on PCC sill

Metal weather bar inmastic

frame bedding

Timber sill ofwindow frame

No mastic pointing here -- left clear to

allow water in cavity to drain out

Bellcast

20 roughcast or dry dash finish

PCC outer lintel

DPC dressed over inner lintel face

Fig. 5.4 Pre-1970s sill and head details, rendered ex-ternal finish.

� Returning the inner leaf of masonry againsta DPC layer on the outer leaf at the jambs.

These details were sound and have stood thetest of time since the early 1900s with onlyminor adjustment. The principles should notbe abandoned for the sake of fashion or whim.They are illustrated in Figures 5.4 and 5.5 in acavity wall which has a roughcast finish.

150 DPC

PCC sill

Window ingo smooth rendered

Stooled endof sill shown

dotted

20 roughcast or dry dashfinish

Outer leaf of wall

Inner leaf of wallMasonrycavityclosure

Mastic pointingTimber sill

outline

15 quadrant

Timber inner sill

Plaster arris reinforced

Horn on timber inner sill

Fig. 5.5 Pre-1970s jamb detail, rendered externalfinish.

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A few important points to note about the de-tails:

� PCC (pre-cast concrete) lintels of that pe-riod were frequently only reinforced at thebottom. Top and bottom reinforcement withlinks is now much more common.

� The roughcast finish stops short of the headand jambs of the timber frame and underthe PCC sill. At both head and sill this al-lows water to drain out. This should not befilled with mastic. At the jambs, the spaceis used to seal frame to wall to DPC withmastic.

� Joints of plaster to timber frame are coveredwith a timber quarter round beading to hidethe joint which would inevitably show acrack as the timber and plaster shrank awayfrom each other.

� Good joinery practice would have the bedmould tongued into a groove in the tim-ber inner sill. Economics now dictates oth-erwise.

� Had the wall been finished with facingbrick, many architects would have left the

Projection of outer leaf and components in itbeyond the inner leaf

While the facing brickwork is on a slightly differentalignment, the omission of the render finish to the outerface of the wall exposes the concrete lintel. This requires

a fair face on all exposed surfaces

Mastic pointingat jambs

No mastic pointing at head

Mastic bedding andpointing between sills

and roundweather bar

Fig. 5.6 Pre-1970s sill, jamb and head details, facing brick external finish.

brickwork in exactly the same position asthe common brick shown, relying in thatcase on the mastic alone to give a weatherseal instead of having the roughcast providea check or rebate. It would be better to havethis small rebate built into the wall as shownin the masonry only outlines of Figure 5.6.

Figure 5.7 is a photograph of the sill and partof the jamb of an opening in a blockwork wall.The details shown are the 200 thick outer leafof masonry; the sill with the upstand withweather bar groove; the weathered surface ofthe sill; the stool on the end of the sill; the lackof protection to the finished surfaces of the silland how dirty they are – not a good site.

Figure 5.8 is a photograph of the same win-dow opening which shows both sill and linteland masonry mullion. The mullion is beddedbetween sill and lintel but is also restrainedin position by metal dowels both top andbottom. Figure 5.9 shows how this would bedone. Note how the sill has a sloping surfacegenerally to make water run to the front edge,and how the underside of the projection has a

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Fig. 5.7 Photograph of 1990s sill and jamb.

groove – the throating – to prevent water run-ning back onto the face of the wall. Becausethe upper surface slopes, the mullion sits ona stool. This device is also used at the endsof sills which are built into walls, to allow themasonry to be bedded on a horizontal surface.

Fig. 5.8 Photograph of 1990s head, sill and mullion inartificial stone.

Mullion

Metal dowel

Groove forweather bar

Hole or morticefor dowel

Stool formullion

Weathered surface of sill

Upstand on whichwindow is bedded

Throatingon sill

Handlingsteel

Fig. 5.9 Detail of mullion–sill junction.

Figure 5.10 is a photograph of the insideof another window on the same site, whichshows a galvanised steel lintel holding up theinner masonry leaf over the opening. Steel lin-tels are sketched a little later in the text.

It is important to note that frames for win-dows or doors are only fastened to the wallsthrough the jambs and that in the traditionalmethods this fastening went into the masonry,closing the cavity.

Figure 5.11 is a photograph of a cavity clo-sure in blockwork. Note how a cut block closes

Fig. 5.10 Steel lintel at inner leaf of opening.

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Fig. 5.11 Detail of checked jamb.

the cavity and bonds into the inner leaf in al-ternate courses, and that a cut of blockwork isused for the intermediate courses, all beddedup solid in mortar and with a vertical stripof DPC between closure and the outer leaf.Compare these photographs with Figure 5.4,the general sections.

For nailing to plugs, proprietary framing an-chors or cramps are the most common meth-ods, although some window frames are stillonly wedged into place. More of this whenwe examine windows in Chapter 9.

Note that in Scotland, traditional practice isto form the opening and then fit the frame intothe opening, whereas the practice in the restof the UK is almost entirely to set the frame upon the sill, rack or brace it vertical, and thenbuild up the rest of the wall round it.

The window sections shown in all thedrawings so far have been based on standardsingle glazed casement windows. A range ofsections will be studied in Chapter 9, Win-dows.

The practice of building in frames as the wallis built up means that fixings are generally

galvanised or stainless steel ‘cramps’ fixed tothe back of the frame and bedded into the mor-tar joints. Screws should be used with timberframes, and machine or self tapping screwswith metal or plastic frames. A typical fixingis shown in Figure 5.12.

Since 1970 there have been several editionsof the Building Regulations, and the stricterrequirements regarding U-values of walls andthe need to avoid cold bridging have meantthat the traditional details have had to be up-dated. This is shown in Figures 5.13 and 5.14.

Back of frame

Screw fixings

Fig. 5.12 Window frame cramp.

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Cavity insulation

PCC inner lintel

12--15 plaster

Extruded polystyrene

cavity closure

Self foaming plastic

Windowhead

25 thick polystyrene

strip behind DPC.Blockwork reduced

to 75 thick

20 roughcast or dry dash

finish

PCC sill

Stooled end ofPCC sill

Sill of windowframe

Bellcast

20 roughcast or dry dash

finish

PCC outer lintel

DPC dressed over inner lintel and

cavity closure

No pointing here -- left clear to allow water

to drain out

Fig. 5.13 Eliminating cold bridging at sill and head.

Variations on finishing

The figures which follow show variationson the finishing of various parts of open-ings incorporating different materials and

Timber inner sillExtruded

polystyrene ascavity closure

Inner leaf

A larger gap can be leftbetween masonry and

frame which can filled withan injected self foaming

plastic

15 quadrant

Outer leaf

20 roughcast or drydash finish Stooled end

of sill

Window ingoessmooth rendered

PCC sill

Masticpointing

DPC

Window cramp built into inner leaf, screwed

to back of window frame

Galv. metal strap screwed to back of window frame and frame anchors into

blockwork

Fig. 5.14 Alternative jamb arrangements and cavityclosure to eliminate cold bridging.

components but always including wall insu-lation and avoiding cold bridging in terms ofthe current Building Regulations. The goodpractice in relation to the positioning of DPCsand frames, and mastic pointing in appropri-ate places, have all been maintained from thepre-1970 details.

Textbooks will show weeps formed or builtinto perpends of the outer leaf of brickworkover window and door openings. This cannotbe done when lintelling with PCC and/or aroughcast finish. How do you build a weepthrough a solid concrete lintel? There weretwo possible routes for water in the cavity touse to escape. The first was between DPC andouter lintel, a space which was never pointedwith mastic, as has been noted on the previ-ous figures. The second was off the ends of theDPC into the cavity itself, but at the back of theouter leaf. This was made easier by the sim-ple expedient of having the DPC project about100 mm beyond the end of each lintel. With noinsulation filling the cavity, water running offthe low end of the DPC did so against the in-ner face of the outer leaf and was in no dangerof crossing back across the cavity.

In recent years in the construction press,much has been made of cavity trays. The DPCover inner lintels is such a tray and in the badold days they formed up from hessian-basedbituminous DPC where appropriate. There isa widely held opinion that the ends of all cav-ity trays should be ‘boxed’ to prevent waterrunning off the end into the cavity. In manyinstances this is correct but is not really neces-sary at ordinary PCC lintels unless the cavityis filled with insulation. There are three solu-tions to the problem: only part fill the cavityand let the water run off the ends of the DPC inthe usual manner, or put the insulation some-where else, completely inside or outside thewall, or redesign the lintelling when we havea facing brick finish.

Alternative lintelling arrangements areshown in Figures 5.15, 5.16 and 5.17. Fig-ure 5.15 shows a steel lintel made upfrom three pressed sections spot welded to-gether, zinc plated, passivated and paintedin the factory. A separate DPC is shown but

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Weep

DPC

Mastic pointing

Self foamingplastic fill

Factory filledwith insulation

Back of lintelperforated

Metal lath to takeplaster finish

Sawn, treatedbatten clipped

to back oflintel

Fig. 5.15 Pressed steel inner lintel (1).

some manufacturers do not recommend one.Figure 5.16 shows an IG lintel, available in gal-vanised steel and stainless steel. Sealing thewindow frame and foam filling etc. is all thesame as the earlier lintels. Figure 5.17 shows avery old form of lintelling when using a facingbrick outer leaf: the mild steel angle iron. Gal-vanised angles are more readily available andare to be preferred to plain steel. Note that the

Cavity insulation

DPC

Factory filled

with insulation

Weep

Fig. 5.16 Pressed steel lintel (2).

Cavityinsulation

Weep

100 x 100 x 12galvanised

m.s. angle iron

PCCinnerlintel

DPC

Fig. 5.17 Angle iron lintel.

inner lintel here is rectangular and that a DPCis dressed over it and down over the angle toproject beyond the angle iron. DPC projectionis necessary in all the details where it is shownto provide a good drip and prevent water be-ing drawn under the lintel and so coming incontact with the frame. Mastic pointing is usedat the head of the frame.

The illustrations so far show an outer leaf offacing brick. All of these lintel alternatives canbe used with a roughcast or dry dash finishon common brick or blockwork. The generaldetail does not alter significantly. The weepscan be blocked when the roughcast is appliedand, if possible, the use of weeps with a re-movable strip or a strict regime of cleaning upafter rendering has to be adopted. Figure 5.18shows a possible solution using the IG linteland without using weeps, instead using thenatural porosity of blockwork to allow waterto escape. The detail would be the same forany steel lintel.

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Bellcast

Mastic pointing

Roughcast cutshort of edge

of lintel

Fig. 5.18 Pressed steel lintel (3).

Before leaving lintels the term ‘bellcast’ re-quires expansion. It is obvious how this pro-jection of a roughcast or rendered finish gotits name. It is not formed directly by applyingthe mortar in that shape; that would not bepossible. Instead, early craftsmen fixed a tem-porary batten to the masonry background andworked to the thickness of that batten. Mod-ern practice uses either a galvanised steel beador a plastic bead, which is fixed to the wall andthe render brought to that. Figure 5.19 shows atypical section and its application, while Fig-ure 5.20 is a photograph of three galvanisedbeads, from the left:

� The bellcast bead.� A render stop bead used to finish off plaster

at an open edge of a wall or where separat-ing plaster or render finishes either side ofan expansion joist etc.

� Angle bead for protecting arrises in plaster-work. It features in most of the sketches inthis book on openings in masonry walls.

Note that all the beads feature a mesh-likefinish to the edges which are bedded intothe plaster or render. This mesh is expanded

Blo

ck b

ackg

roun

dFa

cing

bric

k ba

se

Roughcastor

render

Bellcastbead

Expanded metal edge onbead, nailed or stuck with

mortar to blockwork

Fig. 5.19 Bellcast bead.

Fig. 5.20 Photograph of bellcast bead and corner bead.

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Mastic behind DPC

If ends of DPC boxed,then weeps in here

DPC

Thermabate

Head

Jamb

Thermabate

Mastic

Fig. 5.21 Proprietary cavity closure at head and jambs.

metal and is made by slitting the metal sheetand then pulling it apart.

The only alternative to the use of masonryor extruded polystyrene strip to close cavitiesat jambs is the use of a proprietary closure.The component is an extruded uPVC sectionfilled with expanded plastic foam. The outsidehas grooves or ridges to provide a fixing pointfor fittings and to direct water flow. Becausethe PVC outer is waterproof, there is gener-ally held to be no need to place a separateDPC against the outer leaf. This is not neces-sarily the case when the frame is set back inthe opening, as is common in much contempo-rary construction. Figures 5.21 and 5.22 showhow this can be dealt with.

Various

Flange

PVC casing Foam filled

Flanges and tees totake fittings and

stop water

Fig. 5.22 Schematic of cavity closure.

Alternative sill arrangements

Figure 5.23 shows a PCC sill with a propri-etary closure immediately under the sill ofthe window frame. The flange of the clo-sure should be over the PCC sill, bedded inmastic and trimmed back if necessary. Theprojection of the timber window sill may haveto be larger than usual. Note the use of and po-sition of the DPC. Provided the under sill DPCstarts on the inside face of the closure, thereis no need to place DPC between the closureand the outer leaf at the jambs detail.

An alternative shape for a PCC sill is shownin Figure 5.24. This shape can be cast onecourse high, although it makes a very slendersill if there is a wide window opening.

Tiles, both plain roofing of clay or concreteand quarry floor tiles, make good sills as theyare made to prevent the entry of water. Thedetail is illustrated in Figure 5.25. They must,however, be laid in a minimum of two courseswith the bond broken and in a strong mor-tar, mix 1:5 or even 1:4. Any DPC must bebrought down at least one, preferably two,brick courses below.

Window sill bedded onThermabate with mastic

Stooledend of

sill

DPC

Fig. 5.23 Proprietary cavity closure at sill.

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Outerleaf

Innerleaf

Cavity

Drip

Stooled end

Grooves for weather barfilled with mastic

Insulation to preventcold bridge

Fig. 5.24 Alternative sill in PCC.

Bullnose bricks can be laid on edge to pro-vide a sill. The plain header end is cut to abevel against the inner leaf and the bricksare canted up at the inside end to form aweathering. The sharp arris at the bullnoseend forms a satisfactory drip. A strong mortaris required to provide a reasonably weatherresistant joint. The detail is illustrated in

Cav

ity in

sula

tion

Cold bridgeinsulation

Mastic pointingand bedding

Plain roofingtiles as sill

DPC

Upper coursewith bullnose

Quarry tiles as sill

Fig. 5.25 Tile sills.

Insulation to preventcold bridging

Masticpointing

Bullnose brickbevelled one end

laid BOE

End of brickforms drip

DPC

Outerleaf

InnerleafCavity

Fig. 5.26 Bullnose brick sill.

Figure 5.26. DPCs are best taken one fullcourse below the bullnose sill.

Note that it is only on the PCC sill detailsthat stooled ends are shown because only PCC(or stone) sills are built into the walls at thejambs. Tile and brick sills are built only be-tween the jambs. PCC (and stone) sills are alsomade without stooled ends, to be built into theopening after the walls are complete and ei-ther just before or after the window frames arefixed. Such sills are termed ‘slip sills’.

Threshold arrangements

What a sill is to a window, the threshold isto a door. The same requirements apply – theneed to make this opening joint wind and wa-tertight. Many variations are seen, but withframes recessed into openings, the ideal situ-ation is to provide a step up to the floor levelwith the face of the step in the same plane asthe face of the door. Figure 5.27 shows this de-tail and points out one possible weakness – thefixing of the weather bar. Figure 5.28 shows asolution to that problem which does not jeop-ardise the integrity of the detail but providesa secure anchorage for the weather bar. The

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Platt

DPC

Dotted line showsoutline of slip step

at jamb

Cavity &closure

Outer leaf

ArchitraveSkirting

PlasterPlinthblock

Waist of slip step

Door

Line ofinsideface ofinnerleaf

Doorframe

Stop/facing

FGL

Platt

Laid to fall away from door

Slate or tile as permanentshutter

Slip step

Threshold bar pluggedand screwed to step

Plinth block

Architrave

Inner leaf with plaster

Cavityclosure

DPCOuterleaf

Stop/facing

DPC

FFL

Door frame

Doo

r

3 course corbelto support slip step

Horizontal section above slip stepVertical section through platt, slip step and bottom of door

Inner leaf

Fig. 5.27 Threshold (1).

detail is shown in Figure 5.29 and a photo-graph in Figure 5.30.

Note that the first detail, Figure 5.27, showsthe traditional full width frame in the checkedreveal while the second detail, Figure 5.29,shows a more modern small section frame

with the reveal finished in the same way asthe wall. Note that the second arrangement re-duces the amount of timber used for the doorframe and the stop facing; there are no plinthblocks to make and fix and no architrave; thereare 1

4 round beads; and plaster and skirting

This face in same plane as door

This face projects fro

m face of d

oor

Plugging and screwing the threshold bar to step is in a wider part of the step, just

where the plug expands, so less chance of concrete spalling

Stooled end

Stooled end

Plugging and screwing threshold bar to step is very close to and could spall

the concrete off

Dotted lines indicate position ofthresholds and ends of door frames

Width between stooled endsis door width plus clearance

Indicates a dowel, usually from offcuts of 15copper water pipe, let into bottom of door frameand grouted into hole in step. Dowels stop the

bottom of the door frame from twisting

Slip step shown in Figure 5.27

Slip step shown in Figure 5.29

Fig. 5.28 Slip steps.

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DPC Cavity closure

Outerleaf

Slip step

Stop/facing

Inner leafwith plaster

Door frame

Doo

r

Skirting

1/4 round bead

Threshold plugged andscrewed to step

FFL

Note how stop/facing isscribed to angled face

on slip step and so covers the joint of the cavity

closure to the top of the step -- a better finish than

the previous detail

Platt

FGL

Cavity closedwtih slate/tile

DPC

Platt

DPCStop/facing

Door frame

Face of slip step

Waist of slip step

Door

Cavityclosure

1/4 round beadCorner bead reinforcing arris

Skirting

Vertical section through platt, slip step and bottom of door Horizontal section above slip step

Plaster

Fig. 5.29 Threshold (2).

have to return into the reveal from the wallface. This detail is more economical than thefirst arrangement.

Note that in both details the type of floorhas not been shown. This is irrelevant tothe threshold construction, although for some

Fig. 5.30 Photograph of threshold (2).

floors the DPC under the slip step should beturned up between step and floor – very im-portant if the floor is of hung timber or con-crete construction. For solid concrete floors,the DPC should be joined to the DPM.

It is usual to keep the top of the slip stepslightly higher than the finished floor level ofthe building. This allows for any thickness offloor finish put down by the occupiers such ascarpet, vinyl sheet, etc.

Threshold bars come in a bewildering va-riety of types, sizes, materials and finishes.Some have moving parts (to be avoided,as they inevitably break down); others havefixed sections. Some have only one sectionfixed to the slip step; others have a numberof sections fixed to both slip step and door.

Partitions of masonry

The fitting of door frames into the openings inpartitions can be done using full width or partwidth door frames. The effect is similar to thatseen with the external doors shown earlier.

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Figure 5.31 shows lintelling arrangements.Figure 5.32 shows two typical examples – apart width frame with a PCC lintel and a fullwidth frame with a pressed steel lintel. Thechoice is deliberate as it is difficult to finishthe soffit at a part width frame where there isa pressed steel lintel of this type – how is thefinish attached to the corrugated shape of thelintel? It might be possible to introduce a stripof metal lath, but how can one convenientlyfasten that to the lintel?

Frames for doors in partitions will normallyinclude a timber threshold plate (not to be

2 or 3 brickcourse

multiples

one brickcourse

one brickcourse

Precast concretelintels

Galvanised pressed steel lintels

Depth andreinforcement

for these lintelswill depend onwhether or notthe partition is

load bearing andon the span

Pressed steellintels are made

in a variety ofprofiles for

partition work;those shownhere are only

suitable for non-loadbearing

partitions

Fig. 5.31 Partition lintels.

Plaster

Pla

ster

Plaster Pressed steellintel

Pla

ster

Plaster

Half brickwide

Stop

Doorframe

Architrave Architrave

Skirting lineArchitrave

Architrave

Architrave

Architrave

Door frame

Door frame

Door frame and fixing

Stop

Skirting line

Door

DoorD

oor

Door

Stop

Stop

round bead

round bead

Corner bead toplaster arris

Corner bead toplaster arris

PCC lintel

Skirting line

Skirting line

41

41

Fig. 5.32 Partition door openings.

confused with a threshold bar), a plain tim-ber section, usually hardwood. This may beonly the width of the door (irrespective of theactual frame width) or the width of the frame.From a purely practical point of view, a fullwidth plate is best as any floor covering fittedto the threshold plate does not incur excessivewaste. Indeed, the occupant may be forced topurchase the next width up in floor coveringbecause of the door ‘recess’.

For fastening frames, see Appendix G, par-ticularly nailing to dooks and proprietaryframing anchors. Note in the partial widthframe situation how close the frame fasten-ing is to the edge of the frame, or if it is set inthe middle how close it would be to the edgeof the wall.

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In all the door frames fastened to masonry,3 or 4 frame anchors or plugs should be usedin internal walls and 4 or 5 for external doors,depending on the weight of the door leaf.

Openings in timber frame walls

Openings in timber frame walls share onlythree things in common with masonry walls:

� The need to provide support for the struc-ture built over the opening

� The need to provide a finish to the structurebelow the opening

� The need to close cavities and maintaina waterproof interface with whatever theopenings will accommodate.

Additional features include:

� The need to include fire stopping roundopenings

� Proper weather proofing where the outerskin is of the rain screen variety (this willbe explained as we go along)

� Provision for differential movement atopenings in structures over three storeyshigh between the frame and the facing ma-terial, particularly a facing of masonry. Thiswill not be included in this text.

We begin by looking at suitable details forone- and two-storey buildings with domes-tic or light commercial loadings, in each casetaking different cladding systems/techniquesinto account. As we have done before, we canclassify the openings according to size:

� For small pipes and cables < 50 mm diam-eter

� For pipes and ventilators >50 mm diameterbut <225 mm

� In excess of 225 mm – large openings.

Openings for pipes and cables up to 50 mmdiameter can be treated in the same way, nomatter what the storey height.

When cutting through a timber frame wallfor a pipe or cable, the elements shown inFigure 5.33 will all be pierced and the cav-ity bridged; if not treated properly this will be

Externalcladding

Cavity

Breather membrane

on sheathing

Sheathing

Insulation in voids of timber frame

Vapour control layer

Plasterboard orother finish

Fig. 5.33 Timber frame wall schematic.

a source of potential trouble as the buildingages.

Starting at the inner face, the hole in theplasterboard can be disguised by using a floorplate. Immediately behind is the vapour con-trol layer (VCL) which if badly torn will al-low water vapour to collect in the insulation –a possible source of condensation and rot onthe back of the sheathing. Cutting through thesheathing causes no problems but piercing thebreather membrane could allow solid water topass to the sheathing.

The breather membrane should be cut withan upside down T-shaped cut which forcesany solid water to run round the cut and downthe face of the membrane. This is illustrated inFigure 5.34. Bridging the cavity must be done

Top of slitpoints

upwards

Fig. 5.34 Cutting waterproof fabric for pipe passingthrough.

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Metal pipe or sleeve 50 diameter

Facing brickcladding

Cavity fire stopped atall other openings, top

and bottom and atcorners

102.5 50 110 102.5 50 110Metal pipe or sleevepassing through wall.No need to firestop

around it but must be atight fit in thesheathing.

Loose fit in the facingbrick allows for

differential expansion.

Cable or plastics pipein sleeve. Sleeve

bushed each end toprevent damage from

chafing.Gas pipes need to besealed both ends withan approved mastic

Timber framepanel with 11

OSB sheathingand breatherpaper on 97framing and

VCL and 12.5plasterboard,

decorateddirect

Fig. 5.35 Pipes and ducts through timber frame wall (1).

with any material sloping down towards thecladding, thus preventing solid water reach-ing the breather membrane. Cutting throughthe outer cladding must be done with care,not only from the point of view of appearancebut also to keep the hole to the minimum re-quired, so preventing vermin and larger in-sects getting into the cavity. Larger holes willalso allow weather, particularly rain andwind-driven snow to penetrate. This is moreimportant where the external cladding is ofthe rain screen variety.

Commencing with a masonry layer, Fig-ures 5.35 and 5.36 show some typical exam-ples; the slope to the outside is, of course,exaggerated. In Figure 5.36 a duct is illus-trated which could be circular or rectangular,plastic or metal. Whichever of these combi-nations it is, there is every need for fire stop-ping around it. Sealing of all the ducts, sleevesand pipes to the masonry cladding could bedone, but rather than using the ubiquitous sil-icone sealer, one based on polysulphide mightprove to be more long lasting. There is nothingwrong with silicone sealers but frequently theincorrect grade is used and often in the wrongplaces for a silicone-based product.

The examples shown have only illustrateda cladding of masonry which to some degreeor other will absorb rain driven onto its face.Penetration to the cavity is not a problem asmeasures are built into the general detailingto cope with this, particularly the provisionof a DPC layer between fire stopping andcladding.

Rain screen cladding

Mention was made earlier of rain screencladding. These types of cladding do not ab-sorb water to any great extent and some notat all:� Slightly absorbent claddings include slate

and tile, both clay and concrete, timber suchas shiplap or weather boarding, and boardsmade from timber, asbestos cement or silicafibre cement compounds.

� Non-absorbent claddings include metalsand glass.

Metals and glass are seldom used in domes-tic structures in the UK but are common inNorth America, as are boards of timber fibreand asbestos cement. This leaves tile or slate

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Plastic sleeve < 50 diameter and light metal or plastic duct > 50

Fire stopping

DPC

Firestopping

DPCPlastic sleeve cannot beused for gas pipe

Plastics sleevepassing through

cavity must be firestopped. Can be a

tight fit in facingbrick cladding as

flexibility allows fordifferentialexpansion Light metal or

plastics duct


cladding and timber weather board or shiplapcladding. All are quite common.

Vertical slating and tile hanging is usuallydone on horizontal battens nailed to verticalbattens which in turn are fixed through thebreather paper and sheathing to the studdingof the timber frame. The vertical battens allowa space to be formed from top to bottom of thewall cladding, and this should be finished offtop and bottom to allow a free air flow, thusallowing any water getting past the tiles ontothe breather membrane to dry out.

Timber boarding is normally fixed horizon-tally to vertical battens which in turn are fixedthrough the breather paper and sheathing tothe studding of the timber frame. Shiplapboarding is always fixed horizontally butweatherboarding can be fixed diagonally, al-though this is only done for decorative effect.Any attempt to have timber boarding fixedvertically should be avoided as it defeats therain screening properties of the boards.

Figures 5.37 and 5.38 show the same pipe,sleeve and duct situations already examinedfor a masonry cladding. Here the cladding haschanged to tile, weatherboarding and shiplapboarding.

Permutations of various finishes showingsmall pipe, sleeves or ducts through all thevarious combinations of cladding for timberframe construction would be excessivelyrepetitive here. The details already cov-ered can be extrapolated to cover mostsituations.

Lintels

Large openings are those which require sup-port provided by lintelling over doors andwindows, and here techniques have similari-ties to masonry construction:

� The opening in the timber frame is spannedby a lintel – in this case made from timberor a timber/steel combination.

� The jambs provide support for the lintel bythe insertion of additional studs called crip-ple studs.

� There can be multiple cripple studs in onejamb, some supporting the lintelling ar-rangements and others supporting a sill.

� The bottom of the opening is finished offwith a sill or a threshold

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38 x 25 vertical batten

38 x 25 tile batten

Lead slate piece nailedto tile batten at 50

centres

Code 5 leadslate piece

sized to suit tileor slate withshort spigotburned on.

Pipe passesthrough spigot.Tile cut short tolet pipe pass.Flexibility of

lead, slate ortile allowsdifferentialmovement

Metal pipe

Metal orplastics sleeve

bushed toprevent damageto cable or pipe

Metal pipe 50 diameter Metal sleeve 50 diameter


� Sills require support from cripple studs.� Masonry claddings require support over the

opening and this can be done with con-ventional lintels of concrete or steel or by

special steel lintels restrained against thetimber frame

� Jambs are treated conventionally externallyand internally but the structure within the

Shiplap boarding Weatherboarding

38 x

25

vert

ical

bat

tens

38 x

25

vert

ical

bat

tens

Metal or plastics, pipe orsleeve, through boardingand timber frame wall.

Tight fit in sheathing withcover plates inside and

outside -- see below

Cover plate Sprung lugs

Pipe

Boarding


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\

Full studCripple stud tosupport lintel

Self foaming plastic sealbetween window frame

and cavity closure

Masticpointing

Stooled end ofPCC sill

DPC

50 x 50cavity

closurewrapped in

buildingpaper

12 sheathingplywood

withbuildingpaper

on face

Glass fibrequilt

2/200 x 50 timbersas lintel

DPC

50 x 50 cavityclosure wrapped

in buildingpaper

Inner timber sill

Bed mould

75 x 50 filler piece between studs

150 x 50 sill support on a second cripple stud nailed inside thecripple studs supporting the lintel

150 x 50 studs at 400 centres

12 sheathing plywood with building paper on the face

PCC sill

Window sill beddedin mastic with galv.

weather bar

Self foamingplastic seal

between windowframe and cavity

closure

PCC lintel

20 roughcastor dry dash

Commonbrickwork

12.5 plasterboard andVCL

Fig. 5.39 Window opening in early timber frame constructioin.

jamb is made up of multiple studs and crip-ple studs in the timber frame.

� Masonry sills can be treated convention-ally in all the accepted ways but the ac-tual sill butts back against the timber framepanel with the sill DPC between. The in-ner sill is treated in a conventional mannerwith packers rather than grounds for fixingdown.

Figure 5.39 shows a version of a windowopening in an early timber frame wall. Notethat all the structural timbers were sawn andnot stress graded. These details are fairly typ-ical of early timber frame construction, whichtended to mimic the masonry cavity wall inthe order in which it was built – first the frameswere erected, then the masonry skin was builtand then the openings were filled with win-dows or doors. Now the trend is to erect theframe, fix the cavity closure to the windowor door frames, fix these back to the timberframes and then build the skin against all thetimber work. This does not leave a gap be-tween frame and timber panel to be filled witha sealant.

Figure 5.40 shows the inside of the timberframed panel once it is erected on a wall plate,the doubled top runner put in place and theupper floor joists in place. Note the use of crip-pled studs – studs cut short to provide supportat the ends of horizontal members.

Figure 5.41 shows a more modern approachto timber frame panels. This is a photograph of

Wall plate

Sole plate to frame

Noggings,two in height

Studs at 400 centres

Top runner totimber frame

Double runnerunder joists

Upper floor joistsover studs

Doubled timbersas lintel

Cripple studsupporting

lintel

Filler pieceat sill

Sill support

Cripple studunder sillsupport

Fig. 5.40 Elevation of early timber panel at windowopening.

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Fig. 5.41 Modern timber panel at window opening.

the inside of a timber frame panel but note theOSB skin, the regularised and stress gradedtimbers, the timber lintel supported on dou-ble cripple studs and the narrow sill supporton cripple studs. Now compare with Figure5.40. The studs, runners and dwangs are reg-ularised and 97 × 47 but the studs are put in

Fig. 5.42 Rolled steel channel as lintel in timber panel.

Ring beamJoist

Top runner doubler

Top runner of panel

Timber chock to holdchannel in position

203 x 89 mild steelchannel

Timber under channelgives nailing facility all

round

OSB panelcladding

2 x cripple studs andfull stud of 97 x 47

stress graded timber

Fig. 5.43 Detail of rolled steel channel as lintel in tim-ber panel.

at 600 centres and so the joists are put in at600 centres and have to be much deeper. Afurther complication is the need to keep ceil-ing heights down. If wooden lintelling is usedfor wide openings, the top of the glass in thewindow would be much too low. This can be

Fig. 5.44 Flitched beam over large opening.

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Fig. 5.45 Flitched portal frame round opening in tim-ber panel.

solved in one of two ways depending on theloadings involved.

The first way is shown in Figure 5.42 anduses a combination of a mild steel channelsandwiched between two layers of the 97 × 47timbers, with blocks at each end set into thechannel and nailed to the studs. These keepthe channel in position. Note that there aredoubled cripple studs supporting each endof the channel/timber lintel. Channel ironsare made in a range of sizes but any in therange 76 × 38 to 305 × 89 would be suitable.Figure 5.43 shows a detail at the head of theframe.

The second way is to ‘flitch’ the frame mem-bers – both studs and lintels–to make a ‘portal’round a large opening such as a patio door.Figure 5.44 is a photograph of a flitched beamspanning a wide opening and is followedby a photograph of a flitched portal frame inFigure 5.45. The steel strip in the portal framewas welded at the corners before sandwichingit and bolting up between the timbers. Notethat the steel does not extend to the bottom ofthe jambs but stops short. A plywood packeris put between the timbers.

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