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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