From 3.68 W/m2K to 0.26 W/m2K
The building Joseph Priestley College occupied was built in 1890 and had a U-value for the roof of 3.68 W/m2K. When Crosshall Developments came to convert it into flats they wanted to do better than the 0.35 W/m2K required by Part L and yet have no worries over condensation risk. However, there was a problem because the roof height could not be raised and it was not possible to install extra insulation between the rafters.
Working with TLX Gold, Crosshall Developments came up with a novel solution that achieved a U-value of 0.26 W/m2K.
The Problem: With only 75mm rafters to work with, the developer needed to maximize thermal efficiency of the old roof without raising the roof height or creating a risk of condensation.
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The Solution: The solution was provided by a hybrid system designed by TLX Insulation. The R-value was increased on the outside by draping TLX Gold over the rafters and also improved on the inside by installing 50mm of PIR across the inside of the rafters. Plasterboard was installed in the normal way to finish the job. The result, a U-value of 0.26 W/m2K without a risk of condensation because TLX Gold is certified by the BBA as an insulating breather membrane and does not require a vapour barrier.
