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Thermal Efficiency Title
 
Thermally Efficient Daylight
Part L, energy efficiency and target U values

Rooflights now have to achieve a target U value of 2.2 W/m² K based on a rooflight area of 20%. However, the current Regulations allow both a smaller rooflight area at a higher U value, and a greater rooflight area at a lower U value. Brett Martin Daylight Systems can provide a solution to suit your requirements.

 Thermal Efficiency
Cleartherm
Cleartherm provides the ultimate flexibility in GRP and polycarbonate triple skin rooflights, allowing you to choose the most appropriate U value for your project, with U values from 2.2 W/m²K to 1.0 W/m²K.
The Regulations control the heat loss through the rooflights based on a rooflight area of 20% and a U value of 2.2 W/mK to give the target heat loss figure. The current Regulations allow a trade off between U value and roof area as long as the target heat loss figure isn’t exceeded.
Double skin GRP rooflights can therefore still be used up to a maximum Rooflight area of 14%.
New energy efficiency legislation is due in 2005 and is expected to tighten the regulations further. Cleartherm rooflights can be installed at no extra effort and minimal additional cost, making it sensible to install rooflights with a U value of at least 2.2 W/m² K.
 
Opaque roof area with 0.25W/m² K U value Rooflight area Required rooflight U value W/m² K Rooflight type
69% 31% 1.5 Triple skin GRP or polycarbonate rooflight
80% 20% 2.2 Triple skin GRP or polycarbonate rooflight
86% 14% 3.0 Double skin GRP or polycarbonate rooflight
88% 12% 3.5 Double skin GRP or polycarbonate rooflight
90% 10% 4.1 Double skin GRP or polycarbonate rooflight
 
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