Polycarbonate Roofing Sheet

A polycarbonate roofing sheet is a panel of polycarbonate plastic used where a roof needs to let in daylight. It is widely used for rooflights in industrial roofs, carports, verandas, patio and pergola covers, conservatories and greenhouses. Common forms are corrugated single-wall sheets that match the profile of metal or bitumen sheets, and multiwall (twin-wall, triple-wall) sheets with internal ribs that trap air for insulation.

Material

Polycarbonate was first commercialised in 1958 by Bayer (Makrolon) and in 1960 by General Electric (Lexan), following parallel discoveries in 1953. It is an amorphous thermoplastic with very high transparency, transmitting visible light better than many types of glass.

Key properties

• Impact strength: very tough, with an Izod impact strength of about 600-850 J/m. It can deform considerably without shattering, which is why it is used where hail or breakage is a concern. One corrugated product is marketed as "virtually unbreakable" against hail and debris.
• Scratch resistance: low; many sheets have a hard coating.
• UV: standard polycarbonate yellows and becomes brittle in sunlight, so roofing sheets need a UV-protective co-extruded layer on the outer face. The protected side must face up.
• Thermal movement: a linear expansion coefficient of about 65-70 x 10⁻⁶ per K so fixings need oversized holes and the sheet needs room to move.
• Temperature range: working limits of about -40 °C to 115-130 °C (-40 °F to 240-265 °F).
• Weight: light; one 1 mm (0.04 in) corrugated product weighs about 1.5 kg/m² (0.3 lb/ft²).
• Fire: one corrugated polycarbonate sheet is rated B-s1, d0 for reaction to fire under the European system.

Care

Cleaning should use mild soap or alcohol for grease. Ammonia, acetone, alkaline cleaners and bleach can damage polycarbonate and should be avoided.

Compared with GRP sheets

Glass-reinforced plastic (GRP, "fibreglass") rooflight sheets, made from polyester resin reinforced with glass fibres, are an older alternative. Glass-fibre reinforced plastics date from the late 1930s and 1940s, when Owens Corning's glass fibre and early polyester resins were developed. The two materials behave differently in impact, weathering and fire, so the manufacturer's data for the specific sheet should be checked.

Safety

Plastic rooflights can be fragile, especially as they age. Falls through rooflights are a serious hazard, and roofs with rooflights should be treated as fragile unless proven otherwise.