Openings in Masonry Walls - Blackwell · PDF fileP1: KTU BY019-05 BY019-Fleming-v6.cls...
Transcript of Openings in Masonry Walls - Blackwell · PDF fileP1: KTU BY019-05 BY019-Fleming-v6.cls...
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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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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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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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Openings in Masonry Walls 129
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
Fig. 5.36 Pipes and ducts through timber frame wall (2).
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
Fig. 5.37 Pipes and ducts through timber frame wall (3).
� 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
Fig. 5.38 Pipes and ducts through timber frame wall (4).
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Openings in Masonry Walls 145
\
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.