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Cladding and Curtain Wall Construction 415
ceilings, external fire spread over the fabric and fire spread within concealed spaces such
as cavities.
Fire may spread within a building over the surface of materials covering walls and ceilings.
The Building Regulations prohibit the use of materials that encourage spread of flame
across their surface when subject to intense radiant heat and those which give off appreciable
heat when burning. Limits are set on the use of thermoplastic materials used in rooflights
and lighting diffusers.
To limit the spread of fire between buildings, limits to the size of ‘unprotected areas’ of
walls and also finishes to roofs, close to boundaries, are imposed by the Building Regulations.
The term ‘unprotected area’ is used to include those parts of external walls that may
contribute to the spread of fire between buildings. Windows are unprotected areas as glass
offers negligible resistance to the spread of fire. The Regulations also limit the use of materials
of roof coverings near a boundary that will not provide adequate protection against the
spread of fire over their surfaces.
Smoke and flames may spread through concealed spaces, such as voids above suspended
ceilings, roof spaces, and enclosed ducts and wall cavities in the construction of a building.
To restrict the unseen spread of smoke and flames through such spaces, cavity barriers and
cavity stops must be fixed as a tight-fitting barrier to the spread of smoke and flames.
Resistance to the passage of heat
The interiors of buildings clad with large areas of glass may gain a large part or the whole
of their internal heat from a combination of solar heat gain and from internal artificial
lighting to the extent that there may be little need for supplementary internal heating for
parts of the year. Solar heat gain (and associated solar glare) can be controlled through the
use of simple shading devices fixed externally and/or internally to the building fabric.
Thermal insulation is required to prevent heat from passing through the fabric.
Simply adding layers of insulation to the building fabric does not always provide the preferred
option, especially where aesthetics and space requirements are at a premium. When
space is restricted, advanced forms of insulation are required, some of which are shown in
Table 7.1.
A number of high-performing insulation products are available, such as aerogels and
vacuum insulated panels (Figure 7.1). While they tend to be more expensive than other
insulation products, they offer better thermal resistance for the same thickness. Combined
with more traditional insulation materials, it is possible to reduce thermal bridging and
add an effective thermal barrier within a relatively thin wall.
Ventilation
The use of sealed glazing and effective weather seals to the joints of cladding panels and
windows in the envelope of modern buildings has restricted, and to some extent controlled,
the natural exchange of outside and inside air to provide ventilation of buildings. For
comfort there should be a continuous change of air inside buildings to provide an adequate
supply of oxygen, to limit the build-up of humidity, fumes, body odour and smells, and to
provide a regular movement of air that is necessary for bodily comfort. The necessary
movement of air inside sealed buildings may be induced artificially by mechanical systems
of air conditioning which filter, dry and humidify air through a complex of inlet and extract
ducting, connected to one or more air treatment plants. The pumps necessary to force air