On 15/04/2021 21:38, Theo wrote:
George Miles wrote:
I dont think the problem is condensation,
but that if rain blows in under the slates then there is nowhere for it to go
and no ventilation to dry it out
so the timbers will rot

Generally the advice when insulating with Celotex is to leave some of the
timber exposed, so moisture can escape. Do they not do that with spray foam?

They can't. It is just sprayed directly onto the underside of the slates
and all over the timber.