DIY Doctor

Cold flat roof insulation and possibility of condensation

Postby jhcbed » Sat Feb 27, 2021 9:42 am

I have an existing bitumen flat roof maybe 30 years old but still serviceable. I suspect it must be a cold roof but has had no insulation on the underside. I have taken down the ceilings and there is no evidence of past condensation although it is impossible to adequately ventilate, as the joists run to a blank wall. I was intending to put in 100mm celotex, can this increase the possibility of condensation and sweating problems, logically to me it seems to make it less likely.
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Postby stoneyboy » Sun Feb 28, 2021 10:02 pm

Hi jhcbed
By adding insulation you will reduce the temperature of the space above the insulation, this may mean that the space reaches dew point temperature so condensation will form.
Regards S
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Postby jhcbed » Mon Mar 01, 2021 10:21 am

Thank you I get the logic now
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