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Steel Designers' Manual - 6th Edition (2003)
38 Single-storey buildings
Energy meters should be provided to ensure that comparisons of energy consumption
can be made with those forecast at design stage. These meters in turn will
provide any new owner/tenant with detailed information on which to base future
energy forecasts.
The cladding has also to withstand the applied loads of snow, wind, and foot traffic
during fixing and maintenance. It must also provide the necessary lateral stability
to the supporting purlin and siderail systems. Occasionally it will form part of the
lateral stability of the structure in the form of a stressed-skin diaphragm, mentioned
above.
1.4.8.7 Cladding systems
A variety of systems is available to suit environmental and financial constraints. The
most common are listed below.
Single-skin trapezoidal roofing
This was widely used in the past with plasterboard or similar material as the lining
material, and fibreglass insulation in the sandwich. The construction is susceptible
to the plasterboard becoming damp due to condensation. An alternative is the use
of rigid insulation boards, which are impervious to damp, supported on tee bars
between the purlins. Unless the joints are sealed, which is difficult to achieve, condensation
is likely to form. Although inexpensive, this type is therefore limited in
its applicability.
The minimum slope is governed by the need to provide watertight joints and
fasteners. If manufacturers’ instructions on the use of sealants and stitching to
laps are rigorously followed, this type can be used down to slopes of approximately
4°.
Double-shell roof construction
In this form of construction the plasterboard has been replaced by a steel liner sheet
of 0.4 mm thickness with some stiffening corrugations. The lining is first installed
and fastened to the purlins, followed by the spacing Zeds, insulation and outer sheet.
The liner tray is not designed to take full wind and erection loads, and therefore
large areas should not be erected in advance of the outer skin. The liner tray is normally
supplied in white polyester finish, providing a pleasing internal finish. The
weatherproofing criteria are the same as for single-skin systems and generally the
minimum slope is 4°. Differing thicknesses of insulation are accommodated by
varying spacer depths. The norm is 80 mm of fibreglass giving a nominal U value of
0.44 W/m 2 °C.