COP:natural-light; thermal-expansion

10.7 Thermal Expansion 

 

Although the figures quoted below are the theoretical expansion rates of different plastic roof lighting materials, the actual expansion rate will differ. See 6.2.2 Roof Cladding Expansion Provisions.

As PVC and polycarbonate expand almost six times more than steel, they should only be used in lengths not exceeding 3 m. Translucent plastic sheets, however, do not normally reach the same temperatures as adjoining metal sheets.

10.7A Material Expansion Rates

 mm per 50° C per 1 m length
Steel
GRP
PVC
Polycarbonate
0.6
1.1
7.0
3.2

PVC and polycarbonate sheet in lengths up to 3 m require 6 mm oversize holes to all fixings. The fixings should always be fitted in the centre of the holes, which can be achieved by pilot drilling. It is recommended that a stepped drill bit be used to ensure the correct size hole.

GRP roof lights also require provision for thermal movement, but to a lesser degree. See 6.2.2A Favourable conditions for expansion.

Special screws which drill their own clearance hole are suitable for polycarbonate and GRP sheeting.