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214 Barry’s Advanced Construction of Buildings
Barry’s Introduction to Construction of Buildings. Sheet metal may, in time, suffer corrosion
from heavy condensation on the underside of the sheet. Ventilation to the space between
the sheeting and the insulation, combined with a vapour check to the lining sheets, is the
most effective way of minimising the risk of condensation. Fibre cement sheet is permeable
to water vapour and thus provides less of a risk from condensation.
Resistance to passage of sound
The thin metal skin of profiled metal sheeting affords no appreciable resistance to sound
penetration; thus insulation must be provided, usually via the thermal insulation materials
and effective seals around the opening parts of doors and windows. If sound insulation is
a primary performance requirement, it may be advantageous to adopt a denser form of
enclosure, such as brick or concrete to help provide the necessary sound reduction.
Security
Many single-storey-framed buildings are only occupied during working hours and are
vulnerable to damage by vandalism and forced entry, unless adequately protected through
passive and active security measures. Apart from the obvious risk of forced entry through
doors, windows and rooflights, there is a risk of entry by prising thin profiled sheeting from
its fixing and so making an opening large enough to enter. Given that many buildings clad
with steel sheeting are for warehousing purposes, this presents a serious challenge to the
owners. Where the cost of the goods contained within is high and the likelihood of theft
also high, it is wise to use a more solid form of wall construction, such as brick. Roofs are
more difficult to protect, and some form of secondary protection is often used, such as a
secondary steel cage under the roof (this is outside the scope of this book).
Aesthetics
Choice of an appropriate cladding for the building frame will also be determined by the
appearance of the sheeting used and its ability to withstand weathering for a given timescale.
Sheet profile and colour will be primary concerns, and a wide range of profiles and
colours are available from manufacturers.
Profiled steel sheeting
The advantages of steel as a material for roof and wall sheeting are that its favourable
strength-to-weight ratio and ductility make it both practical and economic to use comparatively
thin, lightweight sheets that can be cold, roll formed to profiles with adequate
strength and stiffness (Figure 4.49 and Figure 4.50). The disadvantage of steel as a sheeting
material is that it suffers rapid and progressive corrosion unless protected. The corrosive
process is a complex electrochemical action that depends on the characteristics of the
metal, atmosphere and temperature, and is most destructive in conditions of persistent
moisture, atmospheric pollution and where different metals are in contact. Typically steel
is protected with a zinc coating by the hot dip galvanising process.
Organic (plastic)-coated profiled steel sheets
The majority of profiled sheets used today are coated with an organic plastic coating to
provide a protective coating and to provide an attractive finish. The plastic coating is
applied to the galvanised zinc-coated steel sheets to serve as a barrier to atmospheric cor-