3 Minute read
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- It’s difficult to achieve the required U-Values with shallow rafters
- TLX Gold can be used without using counter battens
- This School was difficult to work on, but reroofing was made easier by using TLX Gold
75mm rafters? That’s shallow…
Norristhorpe School in West Yorkshire is a large junior and infantâₒs school. Its construction is fairly typical for its age and area, being stonebuilt with steep pitched roofs with dormers. So when the local authority awarded money for upgrading, re-roofing was a priority. But the work had to be carried out in the school holidays. With only 75mm deep rafters and rooms below, insulating with rigid board was not an option given the time constraints.
Fully BBA certified
The contractor who carried out the work, used the BBA certified TLX Gold insulating breather membrane, where it was possible to carry out two jobs in one for the same time and effort.
No counter-battening necessary?
Gold does not need counter-battening if it is used draped over the rafters with the usual 10mm breather membrane sag. The tile battens can then be fitted straight over, with no increase in roof height. And because TLX Gold is fully breathable there is no condensation risk, even without a vapour barrier at ceiling level (provided there is a well-sealed ceiling without gaps letting air through).
If TLX Gold is to be used in this way along with PIR insulation underneath, the rafters canâₒt be fully filled with PIR, since you need to allow the top 50mm to accommodate the TLX Gold plus the unventilated air gap below that allows heat to be reflected back.
If possible, the U Value can be reduced to 0.45 W/m2K
Where circumstances permit, it would be possible to fit 25mm of PIR at the bottom of the 75mm rafter to achieve a U-value of 0.45 W/m2K.
The Problem: How to insulate a school roof at the same time as re-roofing, which was necessary to complete during a time-restricted period.
The Solution: TLX Gold: the BBA certified insulating breather membrane that takes no more time to install than a conventional breather membrane, yet provides insulation with a U-value of 0.69 W/m2K.
