GRP Sheeting is measured in weight per square metre. The test provisions of AS/NZS 4257 require the measure to be calculated from the area of the profile, including the overlap. Because the mass of plastic sheeting varies between profiles, the thickness will vary for different profiles of a given weight per square metre. Deeper profiled products are usually supplied as standard at a greater weight per square metre than more material-efficient profiles.
Standard profiled roof lights are classified as brittle roofing and are not suitable for roof traffic. They are normally laid over safety mesh to AS 4859. (See 13.4.4 Safety Netting)
Trafficable roof lights are normally rendered trafficable by embedding a woven glass mat into the material. They must be tested under the point load test provisions of AS 4040.1, AS/NZS 4040.4, and AS/NZS 1562.3: 2006. Plastic roof lights.
Non-trafficable sheets over one sheet in width should be provided with a walkway, terminate short of ridge and/or eaves, to enable transverse traffic.
The spanning capacity of profiled roof lights depends on the profile shape, material thickness and composition, the number of fasteners per square metre, and the washer type and size.
Pull-though of the fastener is the most common failure mode of profiled translucent sheeting, so it should always be installed with a load spreading washer unless otherwise specified by the manufacturer.
Additional support can be obtained from adjacent metal cladding by using mid-span supports, alternatively, the thickness of the roof lights may be increased.
Profiled translucent sheeting must be designed to be capable of withstanding design wind loads, using the manufacturer’s literature.
