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330 Barry’s Advanced Construction of Buildings
The notional fire resistance times, which depend on the size, height and use of the building,
are chosen as being sufficient for the escape of occupants in the event of fire. The
requirements for the fire resistance of elements of a structure do not apply to:
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A structure that supports only a roof unless:
(a) The roof acts as a floor, e.g. car parking, or as a means of escape
(b) The structure is essential for the stability of an external wall, which needs to have
fire resistance
The lowest floor of the building
To prevent rapid fire spread which could trap occupants, and to reduce the chances of a
fire growing large, it is necessary to subdivide buildings into compartments separated by
walls and/or floors of fire-resisting construction. The degree of subdivision into compartments
depends on:
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The use and fire load (contents) of the building
The height of the floor of the top storey as a measure of ease of escape and the ability
of fire services to be effective
The availability of a sprinkler system, which can slow the rate of growth of fire
The necessary compartment walls and/or floors should be of solid construction sufficient
to resist the penetration of fire for the stated notional period of time in minutes. The
requirements for compartment walls and floors do not apply to single-storey buildings.
Smoke and flame 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
stops should be fixed as a tight-fitting barrier to the spread of smoke and flames.
External fire spread
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.
Resistance to the passage of heat
The requirements for the conservation of power and fuel by the provision of adequate insulation
of roofs are described in Barry’s Introduction to Construction of Buildings and Chapter 3.
Resistance to the passage of sound
A description of the transmission and perception of sound is given in Barry’s Introduction
to Construction of Buildings, Chapter 5. In multi-storey buildings, the structural frame may
provide a ready path for the transmission of impact sound over some considerable distance.
The heavy slamming of a door, for example, can cause a sudden disturbing sound clearly
heard some distance from the source of the sound by transmission through the frame