Cold flat roof insulation and possibility of condensation Information, help and advice on maintaining, installing and repairing a flat roof. Post your questions and view answers here

[jhcbed]

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.

[stoneyboy]

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

[jhcbed]

Thank you I get the logic now