DIY Doctor

Condensation Forming Underneath Loft Board

Postby benawhile » Sun Jan 05, 2020 9:26 pm

I don’t so far have the problem, but a general question with regard to boarding over a loft storage space.
I have found info relating to condensation forming on the underside of loft boards if an air space is not left between the top of the insulation and the underside of the board, but cannot find any definite statement about whether standard loft board is, or should be, water vapour permeable.

There definitely is information on the net to imply that ”building materials “ such as ceiling plasterboard, ARE permeable, and so on pre 1970s houses there is a risk of condensation on the underside of loft board.

Is it best to assume loft board is not permeable, or are there some board materials that have a certain amount of permeability?
benawhile
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Postby benawhile » Mon Jan 06, 2020 6:58 pm

Following from previous post:
I intend to board my loft floor on 7” loft legs after adding glass fibre insulation over the joists.

There are no condensation issues at present and I will continue to monitor this.

The ceiling below is plasterboard from the 1950s and there is no vapour barrier.

My question is, as I cannot verify whether standard loft board is vapour permeable, would I reduce risk of condensation under the boards if I drilled vent holes in them?
benawhile
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