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426 Barry’s Advanced Construction of Buildings
The requirements for resistance to the passage of heat usually necessitate the use of some
material with comparatively good resistance to the transfer of heat, either in the cavity as
cavity fill or partial fill with a lightweight block inner leaf, as illustrated in Figure 7.2. Where
the cavity runs continuously across the face of the structural frame, as illustrated in Figure
7.4, the resistance to the transfer of heat of the wall is uninterrupted. Where a floor slab
supports the outer leaf, as illustrated in Figure 7.2, there will be to an extent a cold bridge
as the brick slips and the dense concrete of the floor slab will afford less resistance to the
transfer of heat than the main cavity wall. The very small area of floor and ceiling may well
be colder. Internal insulation around the floors, ceilings and columns may be used to reduce
the impact of any cold bridges. Where internal insulation is used, vapour barriers should
be used to prevent the warm, moisture-laden air reaching cold surfaces.
7.5 Facings applied to solid and cavity wall backing
The word ‘facings’ is used to describe comparatively thin, non-structural slabs of natural
or reconstructed stone, faience, panels, ceramic and glass tiles or mosaic which are fixed
to the face of, and supported by, solid background walls or to structural frames as a decorative
finish. Common to the use of these non-structural facings is the need for the background
wall or frame to support the whole of the weight of the facing at each storey height
of the building or at vertical intervals of about 3 m, by means of angles or corbel plates. In
addition to the support fixings, restraint fixings are necessary to locate the facing units in
true alignment and to resist wind pressure and suction forces acting on the wall. Fixing
centres are calculated using wind loading software. To allow for elastic and flexural movements
of the structural frame and differential thermal and moisture movements, there must
be flexible horizontal joints below support fixings and vertical movement joints at intervals
along the length of the facings. Both horizontal and vertical movement joints must be sufficiently
flexible to accommodate anticipated movements and must be water resistant to
prevent penetration of rainwater.
Natural and reconstructed stone facings
Natural and reconstructed stone facings are applied to the face of buildings to provide a
decorative finish to simulate the effect of solidity and permanence traditionally associated
with solid masonry. Because of the very considerable cost of preparation and fixing, this
type of facing is mostly used for prestige buildings such as banks and offices in city centres.
Granite is the natural stone much favoured for use as facing slabs for the hard, durable
finish provided by polished granite and the wide range of colours and textures available
from both native and imported stone. Polished granite slabs are used for the fine gloss
surface that is maintained throughout the useful life of a building. To provide a more
rugged appearance, the surface of granite may be honed to provide a semi-polish, flame
textured to provide random pitting of the surface or surface tooled to provide a more
regular rough finish. Granite facing slabs are generally 40 mm thick for work more than
3.7 m above ground and 30 mm thick for work less than 3.7 m above ground.
Limestone is used as a facing, usually to resemble solid ashlar masonry work, the slabs
having a smooth finish to reveal the grain and texture of the material. These comparatively