Flashings - Exterior Wall Assembly

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There’s an old saying that fits this topic very well: the devil is in the details.  at’s because it’s how we  ash windows, doors, porches, chimneys and other key areas of the exterior walls and roof that will keep the water out of your home. Flashings are one of the most important and overlooked components of the building envelope that make or break long-term resistance to damage. Make certain that your framers and roofers are using the right materials for the job and installing them in the proper fashion.  is is not the place to cut money from your budget! Flashings of all sorts are manufactured to  t every joint and intersection of your exterior building envelope, to cover all the different angles, seams, gaps and penetrations. It’s not just the materials; even more importantly, how they are installed keeps the water running downhill.

With windows, the process begins with a sill pan or a layer of waterproof material covering the bottom of the rough opening that the window will be installed in.  is material should be turned up at the corners at least six inches on the inside of the studs and then extend out on top of (not under) the house wrap below the open- ing. The house wrap has a  wrap cut above the window. The window is then installed, and the sides are  flashed with an adhesive tape, followed by a layer of  flashing tape across the top of the window  flange. The  flap of house wrap is then brought down over the top  flange, and it is taped in place with  flashing tape.  The bottom  flange of the window is not flashed.  is will allow any water that does get into the opening to drain out and  ow down the waterproof drainage plane of the house and out the weep holes or screed at the bottom of the wall. By the way, the order that these flashings are installed, from the bottom up, is critical. For curved windows and doors there are flexible flashing tapes on the market now that work very well.

The process for porches and decks is much the same.  e drain- age plane material is fully installed before the ledger board is put in place. A er attaching the ledger board, the drainage plane is cut above the ledger board to which the joists will be attached. A  ash- ing material like metal or  flexible waterproofing is attached to the sheathing, and wrapped around the front of the ledger board.  e drainage plane is then turned down over this flashing and taped in place. You can obtain detailed drawings showing exactly how these openings need to be flashed on the websites of the house wrap or window manufacturer for your project.

The addition of an insulated sheathing to the wall assembly re- duces thermal bridging. Or you can replace the rainscreen assembly that we just described with an insulated sheathing panel system that is taped at all seams (with a 50-year warranty). These types of water management systems are always employed behind masonry or stucco walls (because water penetrates those materials so rapidly) and behind wood walls, too, in rainy or marine climates.

Radiant Barrier - Exterior Wall Assembly

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A radiant barrier is the foil-faced roof decking (with the foil facing the attic side) that stops radiant heat gain through a vented roof assembly in hot climates.  is is usually one of the first upgrades for  existing construction if your roof design allows good access for installation, along with improving the insulation in the attic if needed. Note that radiant barriers require an open, ventilated air space on the side facing the house, so they should not be installed in a sealed attic, as they simply don’t work when foam insulation is in contact with them.

If you live in a cooling-dominated climate, you should also strongly consider using aluminum foil faced radiant barrier roof decking material with an emissivity of 0.05 or less26 to keep your attic cooler in the summer.  is will at least prevent much of the radiant heat gain through the roof assembly.  is results in helping to take some of the heat load o  your air conditioner and ducts during hot weather.

Thermal Barriers - Exterior Wall Assembly

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“ Thermal barrier” is a fancy term for insulation. In a high-performance home, insulation should be installed on all exterior surfaces in an unbroken sequence. Any gaps, voids or breaks in the insulation coverage of the entire building assembly can result in heat loss or gain.  is is shown in the image below with the use of a thermal imaging camera. In a color photo, heat loss shows up as warm yellow or orange and cool well-insulated areas are blue or black. In this black-and-white rendition, light and bright areas indicate heat loss.

Thermal bridging is the rapid transfer of heat through a build- ing component when that component has less thermal resistance (R-value) than materials surrounding it. Framing materials o er a good example of thermal bridging through the building envelope. Wood has an R-value of a little less than one per inch, so a typical 2 × 4 stud has an R-value of around 3.5. Compared to the surround- ing insulated wall cavities, if perfectly installed to manufacturers’ specifications to achieve R-13 or R-19, that’s quite a difference. So, if you look closely at the image above, the thermal movement through the wood-framing members allows you to see all of the studs and even the roof rafters glowing with the heat they are losing. Thermal bridging can greatly reduce the effective insulation value of a wall, floor or ceiling.

Another place where poorly insulated wood is typically used is for structural headers to displace the vertical loads over windows and doors, as was mentioned previously.  is volume of uninsulated wood creates large areas of thermal bridging, significantly reducing the overall thermal performance of the entire wall assembly. As was mentioned earlier, it’s unfortunate that many framing crews are taught to install headers over every window and door, even when they are located in non-load-bearing walls.  is usually hap- pens due to a lack of framing detail provided to them by the structural engineer or truss designer. Best practices are to install headers only where they are required structurally, to size them only for the actual load they are to carry and to insulate them. Many insulated structural header products are available on the market, or you can make your own by sandwiching a rigid foam board panel between two layers of wood (or structural wood product) to create a thermal break.

By adding a layer of rigid board insulation on the exterior of our entire wall assembly, we can reduce or eliminate thermal bridging, as this material provides an insulated break between the wood framing and the exterior heat source. By sealing the attic and insulating over the exposed roof rafters, we can reduce or eliminate thermal bridging there using the same approach. We could also
choose to use an alternative building system, like SIPs, ICFs, AAC block or a natural material, which could significantly reduce thermal bridging in the building assemblies.

We recommended raised heel or energy truss de- sign as a remedy for insulation gaps between the top of the wall assembly and the edge of the roof assembly. It is evident from Figure  that this home suffers from poor insulation in the so t area, a significant source of heat loss in the winter. These are like holes in the thermal envelope, and so the walls perform as if someone has left a window or door open, putting additional strain on the air conditioner or heater as it attempts to provide comfort under these conditions.

Finally, note the heat loss through the foundation or basement perimeter.  is has become a more important issue as we built tighter thermal envelopes, which should enable us to reduce the size of air conditioning and heating systems required to keep them comfortable. However, this heat loss through the foundation assembly can result in raising the heating loads, negating any savings achieved in the main building assembly. In fact, we have seen in- stances in the last couple of years where heat pump system sizing is being determined by these heat losses, driving up heating loads even in cooling-dominated climates with very mild winters.  is means that although we did a good job reducing the cooling loads through building science and envelope improvements, we were forced to install a larger HVAC heat pump system to handle the heat loss through the foundation in the few very cold days of winter that occur.  is is the best argument for insulated slabs in any location that has any chilly winter days. An insulated slab or basement can reduce the heating load on the home by as much as 25 percent or more depending on your climate and house plan.

Rubble walling and random rubble - wall.

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Rubble walling.

Rubble walling has been extensively used for agricultural buildings in towns and villages in those parts of the country where a local source of stone was readily available. The term rubble describes blocks of stones as they come from the quarry. The rough rubble stones are used in walling with little cutting other than the removal of incon venient corners. The various types of rubble walling depend on the nature of the stone used. 

Those stones that are hard and laborious to cut or shape are used as random rubble and those sedimentary stones that come from the quarry roughly square are used as squared rubble.

The various forms of rubble walling may be classified as random rubble and squared rubble.

Random rubble.

Uncoursed random rubble.

Uncoursed random rubble stones of all shapes and sizes are selected more or less at random and laid in mortar, as illustrated in Fig. 1 16A. No attempt is made to select and lay stones in horizontal courses. There is some degree of selection to avoid excessively wide mortar joints and also to bond stones by laying some longer stones both along the face and into the thickness of the wall, so that there is a bond stone in each square metre of walling. At quoins, angles and around openings selected stones or shaped stones are laid to form roughly square angles. 

Random rubble brought to course.
Random rubble brought to course is similar to random rubble uncoursed except that the stones are selected and laid so that the walling is roughly levelled in horizontal courses at vertical intervals of from 600 to 900 mm, as illustrated in Fig. 11 6B. As with uncoursed rubble, transverse and longitudinal bond stones are used.

 Fig. 116 (A) Random rubble uncoursed (B) Random rubble coursed.

Dowels. Cramps - Walls - Stones.

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Dowels.

To maintain parapet stones in their correct position in a wall, slate dowels are used. The stones in a parapet are not kept in position by the weight of walling above and these stones are, therefore, usually fixed with slate dowels. These dowels consist of square pins of slate that are fitted to holes cut in adjacent stones, as illustrated in Fig. 113.

Cramps.

Coping stones are bedded on top of a parapet wall as a protection against water soaking down into the wall below. There is a possibility that the coping (capping) stones may suffer some slight movement and cracks in the joints between theni open up. Rain may then saturate the parapet wall below and frost action may contribute to some movement and eventual damage.
To keep coping stones in place a system of cramps is used. Either slate or non-ferrous metal is used to cramp the stones together.

A short length of slate, shaped with dovetail ends, is set in cement grout (cement and water) in dovetail grooves in the ends of adjacent stones, as illustrated in Fig. 11 5A.

As an alternative a gunmetal cramp is set in a groove and mortice in the end of each stone and bedded in cement mortar, as illustrated in Fig. 115B.

For coping stones cut from limestone or sandstone a sheet metal weathering is sometimes dressed over coping stones. The weathering of lead is welted and tacked in position over the stones.

Fig. 115 (A) Slate cramp. (B) Metal Cramp.

Weathering to cornices, Cement joggle - Stones - Walls

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Weathering to cornices.
Because cornices are exposed and liable to saturation by rain and possible damage by frost, it is good practice to cover the exposed top surface of cornice stones cut from limestone or sandstone with sheet metal, The sheet metal covering is particularly useful in urban areas where airborne pollutants may gradually erode stone.

Sheet lead is preferred as a non-ferrous covering because of its ductility, that facilitates shaping, and its impermeability.

Sheets of lead, code No 5, are cut and shaped for the profile of the top of the cornice, and laid with welted (folded) joints at 2 m intervals along the length of the cornice. The purpose of these comparatively closely spaced joints is to accommodate the inevitable thermal expansion and contraction of the lead sheet. The top edge of the lead is dressed up some 75 mm against the parapet as an upstand, and turned into a raglet (groove) cut in the parapet stones and wedged in place with lead wedges. The joint is then pointed with mortar.

The bottom edge of the lead sheets is dressed (shaped) around the outer face of the stones and welted (folded) To prevent the lower edge of the lead sheet weathering being blow up in high winds, 40 mm wide strips of lead are screwed to lead plugs set in holes in the stone at 750 mm intervals, and folded into the welted edge of the lead, as illustrated in Fig. 114.
Where cornice stones are to be protected with sheet lead weathering there is no purpose in cutting saddle joints.

Fig. 114 Lead weathering to cornice.

Cement joggle.
Cornice stones project and one or more stones might in time settle slightly so that the decorative line of the mouldings cut on them would be broken and so ruin the appearance of the cornice. To prevent this possibility shallow V-shaped grooves are cut in the ends of each stone so that when the stones are put together these matching V grooves form a square hole into which cement grout is run. When the cement hardens it forms a joggle which locks the stones in their correct position.

Cornice an parapet walls, Saddle joint - Walls - Stones.

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Cornice an parapet walls.
It is common practice to raise masonry walls above the levels of the eaves of a roof, as a parapet. The purpose of the parapet is partly to obscure the roof and also to provide a depth of wall over the top of the upper windows for the sake of appearance in the proportion of the building as a whole.

In order to provide a decorative termination to the wall, a course of projecting moulded stones is formed. This projecting stone course is termed a cornice and it is generally formed some one or more courses of stone below the top of the parapet. Figure 113 is an illustration of a cornice and a parapet wall to an ashlar faced building. An advantage of the projecting cornice is that it affords some protection against rain to the wall below.

The parapet wall usually consists of two or three courses of stones capped with coping stones bedded on a dpc of sheet metal. The parapet is usually at least I B thick or of such thickness that its height above roof is limited by the requirements of the Building Regulations as described in Chapter 4 for parapet walls. The parapet may be built of solid stone or stones bonded to a brick backing.

The cornice is constructed of stones of about the same depth as the stones in the wall below, cut so that they project and are moulded for appearance sake. Because the stones project, their top surface is weathered (slopes out) to throw water off.

Fig.113 Cornice and parapet.

Saddle joint.

The projecting, weathered top surface of coping stones is exposed and rain running off it will in time saturate the mortar in the vertical joints between the stones. To prevent rain soaking into these joints it is usual to cut the stones to form a saddle joint as illustrated in Fig. 113. 

The exposed top surface of the stones has to be cut to slope out (weathering) and when this cutting is executed a projecting quarter circle of stone is left on the ends of each stone. When the stones are laid, the projections on the ends of adjacent stones form a protruding semi-circular saddle joint which causes rain to run off away from the joints. 

Openings to stone walls - Lintels.

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A stone lintel for small openings of up to about a metre wide can be formed of one whole stone with its ends built into jambs and its depth corresponding to one or more stone courses. The poor tensile strength of stone limits the span of single stone lintels unless they are to be disproportionately deep.

Over openings wider than about a metre it is usual to form lintels with three or five stones cut in the form of a flat arch. The stones are cut so that the joints between the ends of stones radiate from a common centre so that the centre, or key stone, is wedge-shaped, as illustrated in Fig. 108. The stones are cut so that the lower face of each stone occupies a third or a fifth of the width of the opening.

To prevent the key stone sinking due to settlement and so breaking the line of the soffit, it is usual to cut half depth joggles in the ends of the key stone to fit to rebates cut in the other stones. The joggles and rebates may be cut the full thickness of each stone and show on the face of the lintel or more usually the joggles and rebates are cut on the inner half of the thickness of stones as secret joggles, which do not show on the face, as illustrated in Fig. 108. The depth of the lintel corresponds to a course height, with the ends of the lintel built in at jambs as end bearing. Stone lintels are used over both ashlar and rubble walling.

The use of lintels is limited to comparatively small openings due to the tendency of the stones to sink out of horizontal alignment. For wider openings some form of arch is used.

Fig. 108 Stone lintel with secret joggle joints.

Stone Masonry Walls.

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Before the Industrial Revolution, many permanent buildings in hill and mountain districts and many large buildings in Iowland areas in this country were built of natural stone. At that time the supply of stone from local quarries was adequate for the buildings of the small population of this country. The increase in population that followed the Industrial Revolution was so great that the supply of sound stone was quite inadequate for the new buildings being put up. Coal was cheap, the railway spread throughout the country and cheap mass produced bricks largely replaced stone as the principal material for the walls of ah but larger buildings.

Because natural stone is expensive it is principally used today as a facing material bonded or fixed to a backing of brickwork or concrete. Many of the larger civic and commercial buildings are faced with natural stone because of its durability, texture, colour and sense of permanence. Natural stone is also used as the outer leaf of cavity walls for houses in areas where local quarries can supply stone at reasonable cost.

In recent years much of the time consuming and therefore expensive labour of cutting, shaping and finishing building stone has been appreciably reduced by the use of power operated tools, edged or surfaced with diamonds. This facility has improved output in the continuing and extensive work of repair and maintenance to stone buildings and encourages the use of natural stone as a facing material for new buildings.

Because natural stone is an expensive material, cast stone has been used as a cheaper substitute. Cast stone is made from either crushed natural stone or natural aggregate and cement and water which is cast in moulds. 

The cast stone blocks are made to resemble natural stone.

Vapour barrier: Vapour check, External insulation, Resistance to the passage of sound.

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Vapour check.
The moisture vapour pressure from warm moist air inside insulated buildings may find its way through internal linings and condense to water on cold outer faces. Where the condensation moisture is absorbed by the insulation it will reduce the efficiency of the insulation and where condensation saturates battens, they may rot.

With insulation that is permeable to moisture vapour, a vapour check should be fixed on the room side of insulation. A vapour barrier is one that completely stops the movement of vapour through it and a vapour check is one that substantially stops vapour. As it is difficult to make a complete seal across the whole surface of a wall including all overlaps of the barrier and at angles, it is in effect impossible to form a barrier and the term vapour check should more properly be used. Sheets of polythene with edges overlapped are commonly used as a vapour check, providing the edges of panels or boards of these materials can be tightly butted together. 

External insultation.
Insulating materials by themselves do not provide a satisfactory external finish to walls against rain penetration or for appearance sake and have to be covered with a finish of cement rendering, paint or a cladding material such as tile, slate or weatherboarding. For rendered finishes, one of the inorganic insulants, rockwool or cellular glass in the form of rigid boards, is most suited. For cladding, one of the organic insulants such as XPS, PIR or PUR is used because their low U values necessitate least thickness of board.

As a base for applied rendering the insulation boards or slabs are first bedded and fixed in line on dabs of either gap filling organic adhesive or dabs of polymer emulsion mortar and secured with corrosion resistant fixings to the wall. As a key for the render coats, either the insulation boards have a keyed surface or expanded metal lath or glass fibre mesh is applied to the face of the insulation. The weather protective render is applied in two coats by traditional wet render application, by rough casting or by spray application and finished smooth, coarse or textured. Coarse, spatter dash or textured finishes are preferred as they disguise hair cracks that are due to drying shrinkage of the rendering.

Because the rendering is applied over a layer of insulation it will be subject to greater temperature fluctuations than it would be if applied directly to a wall, and so is more liable to crack. To minimise cracking due to temperature change and moisture movements, the rendering should be reinforced with a mesh securely fixed to the wall, and movement joints should be formed at not more than 6 m intervals. The use of a light coloured finish and rendering incorporating a polymer emulsion will reduce cracking.

As the overall thickness of the external insulation and rendering is too great to be returned into the reveals of existing openings it is usual to return the rendering by itself, or fix some non-ferrous or plastic trim to mask the edge of the insulation and rendering. The reveals of openings will act as thermal bridges to make the inside face of the wall around openings colder than the rest of the wall. Figure 106 is an illustration of insulated rendering applied externally.

Tile and slate hanging, timber weatherboarding and profiled sheets can be fixed over a layer of insulating material behind the battens or sheeting rails to which these cladding materials are fixed.

Slabs of compressed rockwool are cut and shaped with bevel edges to simulate the appearance of masonry blocks. The blocks are secured to the external face of the wall with stainless steel brackets, fixed to the wall to support and restrain the blocks that are arranged with either horizontal, bonded joints or vertical and horizontal continuous joints. An exterior quality paint is then applied to the impregnated surface of the blocks. At openings, non-ferrous or plastic trim is fixed around outer reveals.

Details of insulating materials are given in Table 7. 

Fig. 106 External insulation.

Resistance to the passage of sound.
The requirement of Part E of Schedule 1 to the Building Regulations is that walls which separate a dwelling from another building or from another dwelling shall have reasonable resistance to airborne sound.

Where solid walls of brick or block are used to separate dwellings the reduction of airborne sound between dwellings depends mainly on the weight of the wall and its thickness. A cavity wall with two leaves of brick or block does not afford the same sound reduction as a solid wall of the same equivalent thickness because the stiffness of the two separate leaves is less than that of the solid wail and in consequence is more readily set into vibration.

The joints between bricks or blocks should be solidly filled with mortar and joints between the top of a wall and ceilings should be filled against airborne sound transmission. 

Table 7 Externa insulating materials.

In Approved Document E, giving practical guidance to meeting the requirements of the Building Regulations in relation to walls between dwellings, is a table giving the minimum weight of walls to provide adequate airborne sound reduction. For example, a solid brick wall 215 mm thick, plastered both sides, should weigh at least 300 kg/rn2 including plaster, and a similar cavity wall 255 mm thick, plastered both sides, should weigh at least 415 kg/rn2 including plaster, and a cavity block wall 250 mm thick, plastered both sides, should weigh at least 425 kg/rn2, including plaster.

Solid walls: Mechanical fixing, Internal finish.

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Mechanical fixing.

As alternative to adhesive fixing, the insulating lining and the wall finish can be fixed to wood battens that are nailed to the wall with packing pieces as necessary, to form a level surface. The battens should be impregnated against rot and fixed with non-ferrous fixings. The insulating lining is fixed either between the battens or across the battens and an internal lining of plasterboard is then nailed to the battens, through the insulation.

The thermal resistance of wood is less than that of most insulating materials. When the insulating material is fixed between the battens there will be cold bridges through the battens that may cause staining on wall faces.
Details of some insulating materials used for internal lining are given in Table 6.

Table 6 Internal insulting materials.

Internal finish.

An inner lining of plasterboard can be finished by taping and filling the joints or with a thin skim coat of neat plaster. A plaster finish of lightweight plaster and finishing coat is applied to the ready keyed surface of some insulating boards or to expanded metal lathing fixed to battens. 

Laminated panels of insulation, lined on one side with a plasterboard finish are made specifically for the insulation of internal walls. The panels are fixed with adhesive or mechanical fixings to the inside face of the wall. For internal lining the organic insulants such as XPS, P1 R and PU R have the advantage of least thickness of material necessary due to their low U value.

Solid walls: Adhesive fixing.

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Adhesive fixing directly to the inside wall face is used for preformed, laminate panels and for rigid insulation boards. Where the inside face of the wall is clean, dry, level and reasonably smooth, as, for example, a sound plaster finish or a smooth and level concrete, brick or block face, the laminate panels or rigid insulation boards are secured with organic based, gap filling adhesive that is applied in dabs and strips to the back of the boards or panels or to both the boards and wall. The panels or boards are then applied and pressed into position against the wall face and their position adjusted with a foot lifter.

Where the surface of the wall to be lined is uneven or rough the laminated panels or insulation boards are fixed with dabs of plaster bonding, applied to both the wall surface and the back of the lining. Dabs are small areas of wet plaster bonding applied at intervals on the surface with a trowel, as a bedding and adhesive. The lining is applied and pressed into position against the wall. The wet dabs of bonding allow for irregularities in the wall surface and also serve as an adhesive. Some of the lining systems use secondary fixing in addition to adhesive. These secondary fixings are non-ferrous or plastic nails or screws driven or screwed through the insulation boards into the wall.

Figure 105 is an illustration of laminated insulation panels fixed to the inside face of a solid wall.
Internal insulation is used where solid walls have sufficient resistance to the penetration of rain, an alteration to the external appearance is not permitted or is unacceptable and the building is not occupied. A disadvantage of internal insulation is that as the insulation is at, or close to, the internal surface, it will prevent the wall behind from acting as a heat store where constant, low temperature heating is used.

The principal difficulty with both external and internal insulation to existing buildings is that it is not usually practical to continue the insulation into the reveals of openings to avoid thermal bridges, because the exposed faces of most window and door frames are not wide enough to take the combined thickness of the insulation and rendering or plaster finish.

 Fig. 105 Internal insulation.

Solid walls: Thermal insulation. Internal insulation.

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Thermal insulation.

A requirement of the Building Regulations is that measures be taken, in new buildings, for the conservation of fuel and power. There is no requirement for particular forms of construction to meet the requirement. The practical guidance to the regulation, contained in Approved Document L for dwellings, is based on assumed levels of heating to meet the expectation of indoor comfort of the majority of the largely urban population of this country who are engaged in sedentary occupations.

The advice in the Approved Document is based on an assumption that walls will be of cavity construction with the insulation in the cavity, which is the optimum position for insulation. In consequence it is likely that insulated cavity wall construction will be the first choice for the walls of dwellings for some time to come.

The regulations do make allowance for the use of any form of construction providing the calculated energy use of such buildings is no greater than that of a similar building with recommended insulated construction.
To provide the insulation required to meet the standard for conservation with a solid wall it is necessary to fix a layer of some lightweight insulating material to either the external or the internal face of the wall.

For external insulation it is necessary to cover the insulation material with either rendering, tile, slate or some sheet metal covering as protection against weather. Internal insulation has to be protected with plasterboard or some other solid material to provide an acceptable finish. The cost of the additional materials and the very considerable labour involved is so great that it is an unacceptable alternative to the more straightforward, less expensive and more satisfactory use of cavity wall insulation for new buildings.

Internal insulation.
Internal insulation may be fixed to the solid brick walls of existing buildings where, for example, there is to be a change of use from warehouse to dwelling to enhance the thermal insulation of the external walls. 

Insulating materials are lightweight and do not generally have a smooth hard finish and are not, therefore, suitable as the inside face of the walls of most buildings. It is usual to cover the insulating layer with a lining of plasterboard or plaster so that the combined thickness of the inner lining and the wall have a U value of 0.45 W/m2K, or less.

Internal linings for thermal insulation are either of preformed, laminated panels that combine a wall lining of plasterboard glued to an insulation board or of separate insulation material that is fixed to the wall and then covered with plasterboard or wet plaster. The method of fixing the lining to the inside wall surface depends on the surface to which it is applied.

Brick lintels - walls.

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A brick lintel may be formed as bricks on end, bricks on edge or coursed bricks laid horizontally over openings. The small units of brick, laid in mortar, give poor support to the wall above and usually need some form of additional support.

A brick on-end lintel is generally known as a ‘soldier arch’ or ‘brick on end’ arch. The word arch here is wrongly used as the bricks are not arranged in the form of an arch or curve but laid flat. The brick lintel is built with bricks laid on end with stretcher faces showing, as illustrated in Fig. 97. In building a brick lintel, mortar should be packed tightly between bricks.

A brick on end or soldier arch was a conventional method of giving the appearance of some form of support over openings in fairface brickwork.

For openings up to about 900 mm wide it was common to provide some support for soldier arches by building the lintel on the head of timber window and door frames. The wood frame served as temporary support as the bricks were laid, and support against sagging once the wall was built.

A variation was to form skew back bricks at each end of the lintel with cut bricks so that the slanting surface bears on a skew brick in the jambs, as illustrated in Fig. 97. The skew back does give some little extra stability against sagging.

For openings more than 900 mm wide a brick on end lintel may be supported by a 50 x 6 mm iron bearing bar, the ends of which are built into jambs as illustrated in Fig. 98A. The bearing bar provides little effective support and may in time rust. As a more effective alternative a steel 50 or 75 mm angle is built into jambs to give support to the lintel. The 50 mm flange of the angle supports the back edge of the bricks and may be masked by the window or door frame.

Another method of support was to drill a hole in each brick of the lintel. This can only successfully be done with fine grained bricks such as mans or gaults. Through the holes in the bricks a round-section mild steel rod is threaded and the ends of the rod are built into the brickwork either side of the lintel. This method of supporting the lintel is quite satisfactory but is somewhat expensive because of the labour involved.

A more satisfactory method of providing support for brick on edge lintels is by wall ties cast into a concrete lintel. The lintel bricks are laid on a temporary supporting soffit board. As the bricks are laid wall ties are bedded between joints. An in situ reinforced concrete lintel is then cast behind the brick lintel so that when the concrete has set and hardened the ties give support, as illustrated in Fig. 98B.

Bricks laid on edge, showing a header face, were sometimes used as a lintel. Where the soffit of the lintel is in line with a brick course there has to be an untidy split course of bricks, some 37 mm deep above. Alternatively, the top of the lintel may be in line with a course, as illustrated in Fig. 97.

As support for coursed brickwork over openings a galvanised, pressed steel lintel is used. The lintel illustrated in Fig. 99 is for use with cavity walling to provide support for both the brick outer leaf and the block inner.

 

Fig. 97 Brick lintels.

Fig. 98 (A) Bearing bar for lintel. (B) wall tie support for lintel.

Fig. 99 Steel lintel support.

Boot lintels - Walls.

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When concrete has dried it is a dull, light grey colour. Some think that a concrete lintel exposed for its full depth on the external face of brick walls is not attractive. In the past it was for some years common practice to hide the concrete lintel behind a brick arch or brick lintel built over the opening externally.

A modification of the ordinary rectangular section lintel, known as a boot lintel, was often used to reduce the depth of the lintel exposed externally. Figure 93 is an illustration of a section through the head of an opening showing a boot lintel in position. The lintel is boot-shaped in section with the toe part showing externally. The toe is usually made 65 mm deep. The main body of the lintel is inside the wall where it does not show and it is this part of the lintel which does most of the work of supporting brickwork. Some think that the face of the brickwork looks best if the toe of the lintel finishes just 25 or 40 mm back from the external face of the wall, as in Fig. 94. The brickwork built on the toe of the lintel is usually B thick for openings up to 1.8 m wide. The 65 mm deep toe, if reinforced as shown, is capable of safely carrying the two or three courses of B thick brickwork over it. The brickwork above the top of the main part of the lintel bears mainly on it because the bricks are bonded. If the opening is wider than 1.8 m the main part of the lintel is sometimes made sufficiently thick to support most of the thickness of the wall over, as in Fig. 94.

The brickwork resting on the toe of the lintel is built with bricks cut in half. When the toe of the lintel projects beyond the face of the brickwork it should be weathered to throw rainwater out from the wall face and throated to prevent water running in along soffit or underside, as shown in Fig. 93.

When the external face of brickwork is in direct contact with concrete, as is the brickwork on the toe of these lintels, an efflorescence of salts is liable to appear on the face of the brickwork. This is caused by soluble salts in the concrete being withdrawn when the wall dries out after rain and being left on the face of the brickwork in the form of unsightly white dust. To prevent the salts forming, the faces of the lintel in direct contact with the external brickwork should be painted with bituminous paint as indicated in Fig. 93. The bearing at

ends where the boot lintel is bedded on the brick jambs should be of the same area as for ordinary lintels.

Fig. 93 Boot lintel.

Fig. 94 Boot lintels.

Prestressed concrete lintels and Composite and non-composite lintels- Walls.

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Prestressed concrete lintels 

Prestressed, precast concrete lintels are used particularly over internal openings. A prestressed lintel is made by casting concrete around high tensile, stretched wires which are anchored to the concrete so that the concrete is compressed by the stress in the wires. Under load the compression of concrete, due to the stressed wires, has to be overcome before the lintel will bend.

Two types of prestressed concrete lintel are made, composite lintels and non-composite lintels.

Composite and non-composite lintels.

Composite lintels are stressed by a wire or wires at the centre of their depth and are designed to be used with the brickwork they support which acts as a composite part of the lintel in supporting loads. These comparatively thin precast lintels are built in over openings and brickwork is built over them. Prestressed lintels over openings more than 1200 mm wide should be supported to avoid deflection, until the mortar in the brickwork has set. When used to support blockwork the composite strength of these lintels is considerably less than when used with brickwork.

Non-composite prestressed lintels are made for use where there is insufficient brickwork over to act compositely with the lintel and also where there are heavy loads.

These lintels are made to Suit brick and block wall thicknesses, as illustrated in Fig. 92. They are mostly used for internal openings, the inner skin of cavity walls and the outer skin where it is covered externally.

Precast, or prestressed lintels may be used over openings in both internal and external solid walls. In external walls prestressed lintels are used where the wall is to be covered with rendering externally and for the inner leaf of cavity walls where the lintel will be covered with plaster.

Precast reinforced concrete lintels may be exposed on the external face of both solid and cavity walling where the appearance of a concrete surface is acceptable.

Fig. 92 Prestressed lintels.

Reinforcing rods and Casting lintels - Walls.

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Reinforcing rods.

Reinforcing rods are usually of round section mild steel 10 or 12 mm diameter for lintels up to 1.8 m span. The ends of the rods should be bent up at 900 or hooked as illustrated in Fig. 91.

The purpose of bending up the ends is to ensure that when the lintel does bend the rods do not lose their adhesion to the concrete around them. After being bent or hooked at the ends the rods should be some 50 or 75 mm shorter than the lintel at either end. An empirical rule for determining the number of 12mm rods required for lintels of up to, say, 1.8 m span is to allow one 12mm rod for each half brick thickness of wall which the lintel supports. 

 Fig. 91 Ends of reinforcing rods.

Casting lintels.

The word ‘precast’ indicates that a concrete lintel has been cast inside a mould, and has been allowed time to set and harden before it is built into the wall.

The words ‘situ-cast’ indicate that a lintel is cast in position inside a timber mould fixed over the opening in walls. Whether the lintel is precast or situ-cast will not affect the finished result and which method is used will depend on which is most convenient.

It is common practice to precast lintels for most normal door and window openings, the advantage being that immediately the lintel is placed in position over the opening, brickwork can be raised on it, whereas the concrete in a situ-cast lintel requires a timber mould or formwork and must be allowed to harden before brickwork can be raised on it.

Lintels are cast in situ, that is in position over openings, if a precast lintel would have been too heavy or cumbersome to have been easily hoisted and bedded in position.

Precast lintels must be clearly marked to make certain that they are bedded with the steel reinforcement in its correct place, at the bottom of the lintel. Usually the letter ‘T’ or the word ‘Top’ is cut into the top of the concrete lintel whilst it is still wet.

Head of openings in solid walls and Timber lintels.

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Head of openings in solid walls.
Solid brickwork over the head of openings has to be supported by either a lintel or an arch. The brickwork which the lintel or arch has to support is an isosceles triangle with 600 angles, formed by the bonding of bricks, as illustrated in Fig. 89. The triangle is formed by the vertical joints between bricks which overlap 1/4 B. In a bonded wall if the solid brickwork inside the triangle were taken out the load of the wall above the triangle would be transferred to the bricks of each side of the opening in what is termed ‘the arching effect’.

Lintel is the name given to any single solid length of timber, stone, steel or concrete built in over an opening to support the wall over it, as shown in Fig. 89. The ends of the lintel must be built into the brick or blockwork over the jambs to convey the weight carried by the lintel to the jambs. The area of wall on which the end of a lintel bears is termed its bearing at ends. The wider the opening the more weight the lintel has to support and the greater its bearing at ends must be to transmit the load it carries to an area capable of supporting it. For convenience its depth is usually made a multiple of brick course height, that is about 75 mm, and the lintels are not usually less than 150 mm deep. 

 Fig. 89 Head of openings.

Timber lintels.

Up to the beginning of the twentieth century it was common practice to support the brickwork over openings on a timber lintel. Wood lintels are less used today because wood may be damaged during a fire and because timber is liable to rot in conditions of persistent damp.

Bonding of bricks at rebated jambs - Walls.

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 Just as at an angle or quoin in brickwork, bricks specially cut have to be used to complete, or close, the 1/4 B overlap caused by bonding, so at jambs special closer bricks B wide on face have to be used.

Provided that the outer reveal is 1/4 B wide, the following basic rules will apply irrespective of the sort of bond used or the thickness of the wall. If the rebate is B deep the bonding at one jamb will be arranged as illustrated in Fig. 88. In every other course of bricks a header face and then a closer of 1/4 B wide face must appear at the jamb or angle of the opening. To do this and at the same time to form the 1/4 B deep rebate and to avoid vertical joints continuously up the wall, two cut bricks have to be used.

These are a bevelled bat (a ‘bat’ is any cut part of a brick), which is shaped as shown in Fig. 88, and a king closer, which is illustrated in Fig. 88. Neither of these bricks is made specially to the shape and size shown, but is cut from whole bricks on the site.

In the course above and below, two other cut bricks, called bevelled closers, should be used behind the stretcher brick. These two bricks are used so as to avoid a vertical joint. Figure 88 shows a view of a bevelled closer. 

Fig. 88 Bonding at rebated jambs.

Where the rebate is 1/2 B deep the bonding is less complicated. An arrangement of half bats as quoin header and two bevelled closers in alternate courses for English bond and half bats and king closers in alternate courses for Flemish bond is used.

Jambs of openings and Rebated jambs - Walls.

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Jambs of openings.
The jambs of openings for windows and doors in solid walls may be plain (square) or rebated.

Plain or square jambs are used for small section window or door frames of steel and also for larger section frames where the whole of the external face of frames is to be exposed externally. The bonding of brickwork at square jambs is the same as for stop ends and angles with a closer next to a header in alternate courses to complete the bond.

Rebated jambs.

Window and door frames made of soft wood have to be painted for protection from rain, for if wood becomes saturated it swells and in time may decay. With some styles of architecture it is thought best to hide as much of the window frame as possible. So either as a partial protection against rain or for appearance sake, or for both reasons, the jambs of openings are rebated.

Figure 87 is a diagram of one rebated jamb on which the terms used are noted.

As one of the purposes of a rebated jamb is to protect the frame from rain the rebate faces into the building and the frame of the window or door is fixed behind the rebate.

The thickness of brickwork that shows at the jamb of openings is described as the reveal. With rebated jambs there is an inner reveal and an outer reveal separated by the rebate.

The outer reveal is usually 1/2 B wide for ease of bonding bricks and may be 1 B wide in thick solid walling. The width of the inner reveal is determined by the relative width of the outer reveal and wall thickness.

The depth of the rebate is either 1/4 B (about 51 mm) or 1/2 B (102.5mm). A 1/4 B rebate is used to protect and mask solid wood frames and the 1/2 B deep rebate to protect and mask the box frames to vertically sliding wood sash windows. The 1/2 B deep rebate virtually covers the external face of cased wood frames  to the extent that a window opening appears to be glass with a narrow surround of wood.

Fig. 87 Rebated jamb.