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  • In exposed positions such as high ground, on the coast and where there is little shelter from trees, high ground or surrounding buildings it may well be advisable to employ a system of weathering on the outer face of both solid and cavity walling to provide protection against wind driven rain. The two systems used are external rendering and slate or tile hanging.

    Rendering

    The word rendering is used in the sense of rendering the coarse texture

    of a brick or block wall smooth by the application of a wet mix of lime, cement and sand over the face of the wall, to alter the appear­ance of the wall or improve its resistance to rain penetration, or both. The wet mix is spread over the external wall face in one, two or three coats and finished with either a smooth, coarse or textured finish while wet. The rendering dries and hardens to a decorative or protective coating that varies from dense and smooth to a coarse and open texture.

    Stucco is a term, less used than it was, for external plaster or rendering that was applied as a wet mix of lime and sand, in one or two coats, and finished with a fine mix of lime or lime and sand, generally in the form imitating stone joints and mouldings formed around projecting brick courses as a background for imitation cornices and other architectural decorations. To protect the com­paratively porous lime and sand coating, the surface was usually painted.

    The materials of an external rendering should have roughly the same density and therefore permeability to water as the material of the wall to which it is applied. There are many instances of the application of a dense rendering to the outside face of a wall that is permeable to water, in the anticipation of protecting the wall from rain penetration. The result is usually a disaster.

    A dense sand and cement rendering, for example, applied to the face of a wall of porous bricks, will, on drying, shrink fiercely, pull away from the brick face or tear off the face of the soft bricks, and the rendering will craze with many fine hair cracks over its surface. Wind driven rain will then penetrate the many hair cracks through which water will be unable to evaporate to outside air during dry spells and the consequence is that the wall behind will become more water logged than before and the rendering will have a far from agreeable appearance.

    Slate and tile hanging

    Fig. 85 Slate hangingIn positions of very severe exposure to wind driven rain, as on high open ground facing the prevailing wind and on the coast facing open sea, it is necessary to protect both solid and cavity walls with an external cladding. The traditional wall cladding is slate or tile hanging in the form of slates or tiles hung double lap on timber battens nailed to counter battens. Slate hanging has generally been used in the north and tile in the south of Great Britain. Either natural or manufactured slates and tiles can be used.

    As a fixing for slating or tiling battens, 50 x 25 mm timber counter battens are nailed at 300 mm centres up the face of the wall to which timber slating or tiling battens are nailed at centres suited to the gauge (centres) necessary for double lap slates or tiles, as illustrated in Fig. 85.

    As protection against decay, pressure impregnated softwood timber battens should be used and secured with non-ferrous fixings to avoid the deterioration and failure of steel fixings by rusting.

    Where slate or tile hanging is used as cladding to a solid wall of buildings normally heated, then the necessary insulation can be fixed to the wall behind the counter battens. Rigid insulation boards of organic or inorganic insulation are fixed with a mechanically oper­ated hammer gun that drives nails through both the counter battens, a breather paper and the insulation boards into the wall.

    For vertically hung slating it is usual to use one of the smaller slates such as 405 x 205 mm slate which is headnailed to 50 x 25 mm bat­tens and is less likely to be lifted and dislodged in high wind than longer slates would be. Each slate is nailed with non-ferrous nails to overlap two slates below, as illustrated in Fig. 85, and double lapped by overlapping the head of slates two courses below.The continuous layer of breather paper, that is fixed between the counter battens and the insulation, is resistant to the penetration of water in liquid form but will allow water vapour to pass through it. Its purpose is to protect the outer surface of the insulation from cold air and any rain that might penetrate the hanging and to allow movement of vapour through it.

    At angles and the sides of openings a slate one and a half the width of slates is used to complete the overlap. This width of slate is specifically used to avoid the use of a half width slate that might easily be displaced in wind.

    Fig. 86 Tile hanging

    Internal and external angles are weathered by lead soakers – hung over the head of slates – to overlap and make the joint weathertight. Slate hanging is fixed either to overlap or butt to the side of window and door frames with ‘exposed edges of slates pointed with cement mortar or weathered with lead flashings.

    At lower edges of slate hanging a projection is formed on or in the wall face by means of blocks, battens or brick corbel courses on to which the lower courses of slates and tiles bell outwards slightly to throw water clear of the wall below.

    Tile hanging is hung and nailed to 40 x 20 mm tiling battens fixed at centres to counter battens to suit the gauge of plain tiles. Each tile is hung to battens and also nailed, as security against wind, as illustrated in Fig. 86.

    At internal and external angles special angle tiles may be used to continue the bond around the corner, as illustrated in Fig. 86. As an alternative and also at the sides of openings tile and a half width tiles may be used with lead soakers to angles and pointing to exposed edges or weathering to the sides of the openings.

    As weather protection to the solid walls of buildings with low or little heat requirements the hanging is fixed directly to walling and to those buildings that are heated the hanging may be fixed to external or internal insulation for solid walling and directly to cavity walling with cavity insulation.

     

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  • Strength and Stability

    Up to the middle of the twentieth century the design and construction of small buildings, such as houses, was based on tried, traditional forms of construction. There were generally accepted rule of thumb methods for determining the necessary thickness for the walls of small buildings. By and large, the acceptance of tried and tested methods of construction, allied to the experience of local builders using traditional materials in traditional forms of construction, worked well. The advantage was that from a simple set of drawings an experienced builder could give a reasonable estimate of cost and build and complete small buildings, such as houses, without delay.
    With the increasing use of unfamiliar materials, such as steel and concrete, in hitherto unused forms, it became necessary to make calculations to determine the least size of elements of structure for strength and stability in use. The practicability of constructing large multi-storey buildings provoked the need for standards of safety in case of fire and rising expectations of comfort and the need for the control of insulation, ventilation, daylight and hygiene.
    During the last 50 years there has been a considerable increase in building control, that initially was the province of local authorities through building bylaws, later replaced by national building regula¬tions. The Building Regulations 1985 set out functional requirements for buildings and health and safety requirements that may be met through the practical guidance given in 11 Approved Documents that in turn refer to British Standards and Codes of Practice.
    In theory it is only necessary to satisfy the requirements of the Building Regulations, which are short and include no technical details of means of satisfying the requirements. The 11 Approved
    Documents give practical guidance to meeting the requirements, but there is no obligation to adopt any particular solution in the documents if the requirements can be met in some other way.
    The stated aim of the current Building Regulations is to allow freedom of choice of building form and construction so long as the stated requirements are satisfied. In practice the likelihood is that the practical guidance given in the Approved Documents will be accepted as if the guidance were statutory as the easier approach to building, rather than proposing some other form of building that would involve calculation and reference to a bewildering array of British Standards and Codes and Agrement Certificates.
    In Approved Document A there is practical guidance to meeting the requirements of the Building Regulations for the walls of small buildings of the following three types:
    (1) residential buildings of not more than three storeys
    (2) small single storey non-residential buildings, and
    (3) small buildings forming annexes to residential buildings (including garages and outbuildings).
    Limitations as to the size of the building types included in the guidance are given in a disjointed and often confusing manner.

    Height

    The maximum height of residential buildings is given as 15 m from the lowest ground level to the highest point of any wall or roof, whereas the maximum allowable thickness of wall is limited to walls not more than 12 m. Height is separately defined, for example, as from the base of a gable and external wall to half the height of the gable. The height of single storey, non-residential buildings is given as 3 m from the ground to the top of the roof, which limits the guidance to very small buildings. The maximum height of an annexe is similarly given as 3 m, yet there is no definition of what is meant by annexe except that it includes garages and outbuildings.

    Width

    The least width of residential buildings is limited to not less than half

    the height. A diagram limits the dimensions of the wing of a residential building without defining the meaning of the term ‘wing’, which in the diagram looks more like an annexe than a wing. Whether the arms of a building which is ‘L’ or ‘LP shaped on plan are wings or not is entirely a matter of conjecture. How the dimensions apply to semi-detached buildings or terraces of houses is open to speculation. In seeking to give practical guidance to meeting functional requirements for strength and stability and at the same time impose limiting dimensions, the Approved Document has caused confusion. One further limitation is that no floor enclosed by structural walls on all sides should exceed 70 m2 and a floor without a structural wall on one side, 30 m2. The floor referred to is presumably a suspended floor, though it does not say so. As the maximum allowable length of wall between buttressing walls, piers or chimneys is given as 12 m and the maximum span for floors as 6 m, the limitation is in effect a floor some 12 x 6 m on plan. It is difficult to understand the need for the limitation of floor area for certain ‘small’ buildings.

     

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  • These thin blocks, usually 60 or 75 mm thick, are made with the same lightweight aggregate as those in Class 2. These blocks are more expensive than dense aggregate blocks and are used principally for non-loadbearing partitions. These blocks are manufactured as solid, hollow or cellular depending largely on the thickness of the block.

    The thin blocks are solid and either square edged or with a tongue and groove in the short edges so that there is a mechanical bond between blocks to improve the stability of internal partitions. The poor structural stability may be improved by the use of storey height door linings which are secured at floor and ceiling level.

    Thin block internal partitions afford negligible acoustic insulation and poor support for fittings, such as book shelves secured to them.
    The thicker blocks are either hollow or cellular to reduce weight and drying shrinkage.

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