vapour barrier

Eve1

Does anybody know if it is necessary to put in a vapour barrier if you use xtratherm rigid insulation or does the foil act as a vapour barrier?

Thanks
Eve

Steve

AFAIK Xtratherm have a helpline for this. I reckon you don't need a vapour barrier. The dew point will normally be outside the foil layer - not always the case though, depends on the construction - give them a call and they'll advise you.

patrido

i asked both kingspan and xtratherm about this (specifically in relation to insulated plasterboard).

xtratherm say...

The foil facing on our boards, much like the Kingspan material, is gas and vapour tight and acts as a vapour CHECK – however – every time you cut the board, you cut the vapour barrier. It is recommended that you install a continuous vapour control layer to the under side of a dormer roof such as yours. This ideally should be placed directly behind the plasterboard in the form of polythene or taping the joints on the insulation boards with aluminium foil tape. If you are using a composite board of insulation and plasterboard to the underside of the slope, ensure the boards are tightly butted and sealed.

while kingspan say

Thank your for your enquiry. There is no requirement for a separate vapour control layer when using our TW56 or TW52 Insulated plasterboard as there is a built in vapour control between the Plasterboard and Insulation on these products.

so i guess you make your own mind up.

Eve1

Thanks for that,
I think I'll look into seeing if there is anything else you can use as opposed to plastic.

Eve

anon1

Try ecological building systems in Meath