Rooflights bring natural daylight into the interiors of industrial, commercial, recreational and agricultural buildings. The most common roofl ights used with profi led roof sheeting are translucent sheets made to the same profi le shape as the metal or fi bre cement sheets.
Rooflights bring natural daylight into the interiors of industrial, commercial, recreational and agricultural buildings. The most
common roofl ights used with profi led roof sheeting are translucent sheets made to the same profi le shape as
the metal or fi bre cement sheets.
Materials for roofl ights fall into two categories –
thermosetting plastics (GRP or glass-reinforced polyester) and thermoplastics (acrylic,
polycarbonate and PVC).
Plastics have large coeffi cients of thermal expansion, meaning they expand with a rise in temperature
and contract with a decrease in temperature and that the rate of expansion/contraction is much greater than
that occurring in steel. The dimension changes take place in all directions. Expansion/contraction
movement across the width of the sheets is absorbed by the “accordion” effect given by the sheet
corrugations, but movement along the length requires special attention.
The rate of longitudinal expansion of GRP, per °C of temperature change, is twice that of steel, or
about the same as aluminium. The thermoplastics expand to a far greater extent – three times more
than aluminium and six times more than steel.
All plastic roofl ight sheets require oversized holes around the sheet-to-structure fasteners to allow
the sheets to move freely. These holes can be made either by pre-drilling, or using specially designed selfdrilling
screws with large wings on their shanks.
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