building paper

[Damo1176]

I have just redone the insulation in my loft which previous to this work was less than 75mm. HOwever after installing it all I came across a document that said about reflective foil buildingpaper and brown paper. It said that I should put paper under my loft insulation to stop moisture. Is this true and should I do it before I start boarding. I have kept the insulation back from the eaves and although my soffits have no venting I live mid terrrace so expect air flow to be continuios from the neghbours as well which are vented. I also have found damage to the roof lining underthe tiles and was originally going to use new roof felt to fix but thought that this may also provide some extra ventilation.

Any thoughts from anyone?

 

[JohnD]

When you apply permeable insulation, you are supposed to have a vapour barrier on the warm (e.g. ceiling) side. The idea is that otherwise water vapour will pass through the insulating layer, and as it approaches the cold surface, it will condense within the insulation. I am told this is a particular problem in the walls of cold stores.

If you have foil-backed plasterboard on the ceilings that should fix it, I just have a couple of coats of silk emulsion on my ceilings, and of course an extractor fan in the bathroom, and have never found traces of damp in the insulation. I have a boarded loft with space between the boards and the insulation

I suspect that a lot of people don't bother, maybe you won't have a problem either.