DIY Doctor UK DIY Forums

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.

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

Thank you I get the logic now