Natural Light Materials
The most common form of natural roof lighting used in commercial and industrial buildings comprises single skin, glass-reinforced plastic (GRP) sheets matching the profile of the metal roofing, running from ridge to eaves in continuous lengths of up to 12 m, sometimes longer. For other applications such as housing, polycarbonate sheeting is more commonly used. Polycarbonate is available in stock sheet lengths of up to 7.2 metres.
Profiled PVC roof lights are now rare as they suffer from embrittlement when exposed to UV.
GRP combines polyester resin and chopped glass fibre. AS/NZS 4256.3 requires sheets to contain a minimum of 22% glass fibre by mass and to be marked with their classification and weight.
Comparison of GRP and Polycarbonate.
| GRP | Polycarbonate |
|---|---|
| Available in all profiles | Available in limited profiles |
| Available in long run | Available in standard lengths |
| Available in different thicknesses | Available in one thickness |
| Durability >25 years | Durability >25 years |
| Will lose transparency with age | Will maintain initial transparency |
| Gives diffuse light | Gives direct light |
| Thermal expansion 2 x that of steel | Thermal expansion 5x that of steel |
| Available in tinted or opaque | Available tinted |
| Reasonable light transparency | Excellent light transparency |
Polycarbonate is more popular for shorter runs and continuous widths, where clarity and stable appearance are considered an aesthetic attribute.
Stand-alone and flat-sheet roof lights may be manufactured from translucent or transparent polycarbonate, acrylic, or glass sheeting.
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