To provide for thermal expansion, all profiled roof lighting must be fitted with fasteners installed through an oversize hole and with a load spreading washer. Some fasteners drill their own clearance holes, otherwise pre-drilling is required. Although GRP has approximately twice the expansion as steel, it absorbs less energy from the sun, so the same expansion allowances as used for the adjacent steel sheet can be applied.
Roof netting and safety mesh can damage GRP through expansion movement and walking traffic. GRP can be protected at the purlin by placing a small slip sheet of GRP between the netting and the roof light.
Polycarbonate sheets expand more than steel, and so are only available in lengths up to 7.2 m. When directly installing polycarbonate sheets, friction tape can be placed on the purlins to reduce thermally induced noise.
Manufacturers recommend side lap fasteners on translucent sheets to maintain the integrity of the side laps.
Turn up stop ends are not easily formed with profiled skylights. To prevent blow over at the upper end of sheets, an angle or odd leg J-shaped channel is normally attached to the upper end of sheets with rivets and sealed with silicon or MS sealant.