Thermoplastic rooflights - specification guide

The term 'thermoplastic' covers a huge variety of materials, some of which have been used as an alternative to glass in rooflights and other glazing applications since the 1950s and 60s. In recent years, increasing expectations in terms of performance and regulatory compliance, have led to many thermoplastic materials being discontinued by rooflight manufacturers.

The notable exception is Polycarbonate, which has been developed to provide excellent properties for all kinds of rooflighting applications.

Polycarbonate is a versatile material, available in three sheet forms:

• Solid – Flat or Domed
• Profiled
• Multiwall

The key properties of polycarbonate are common to all forms – exceptional impact resistance, high levels of light transmission, good workability and good fire rating. All are commonly available in clear and tinted options, with clear and most tints providing direct light, while clear patterned and opal tint provides diffused light and gives a soft quality to the light. Co-extruded UV protection eliminates up to 99% of UV radiation, protecting materials and people beneath it. Each form also has its own particular characteristics and properties.

Solid polycarbonate offers good optical clarity and superb workability. It can be cold curved on site and is suitable for use with a variety of glazing bar systems. Polycarbonate is a thermoplastic material, so it can be easily formed into 3D shapes, making it the ideal choice for domes, pyramids and barrel vaults.

Profiled polycarbonate matches profiled roof cladding and allows the sky above to be seen through a corrugated material, a feature popular with many designers. It has very good profile accuracy and is available in a growing profile range. Extrusion and vacuum forming techniques allow a huge variety of profiles to be produced.

Multiwall polycarbonate is an insulating glazing material. Thicker sheets with more walls achieve the highest thermal performance, typically 1.6W/m2K for a 25mm five wall sheet. Structured polycarbonate is most commonly used in most domestic and many commercial conservatories. Like solid polycarbonate it can be cold curved on site, although to a much lesser degree, it can be used in a variety of glazing bar systems, and has a very high strength to weight ratio making it ideal for the creation of glazing features.

 

If you have any queries relating to the specification of thermoplastic rooflights, please contact the NARM technical committee admin@narm.org.uk

Further detailed information for specifiers can be found on our Downloads page.