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Further insulating a warm roof

I have a flat roofed small extension to the house built back in the 70's I believe. It has a warm roof however the insulation is only 50mm thick so the room is very cold in winter. There is a service void approx 150mm deep due to the joists where a few wires and radiator pipes are run. I have been given some 50mm celotex boards which I could cut up and stuff between the joists. Could this cause any issues (condensation etc)?

4 Answers from MyBuilder Roofers

Best Answer

The easiest way to achieve good insulation value to a flat roof would be to install a new warm roof on top and stripping off the old coverings first.


Answered 10th Aug 2020

If it’s a true warm roof then you can fill the void between joists with insulation


Answered 10th Aug 2020

Just make sure you leave a gap for airflow to the underside and maybe some vents in the fascia


Answered 10th Aug 2020

Sounds to me like you’re trying to create a cold roof insulation and a warm roof insulation at the same time would be better to strip flat roof and insulate from above using 100/150mm euro deck then making fascia bigger on the outside to box it back in


Answered 21st Aug 2020

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