DIY Doctor

Insulating Timber Frame and Roof Parts of Bay Window

Postby chameleon001 » Mon Jul 31, 2017 7:41 am


I am trying to figure out the best way to insulate the timber frame and roof part of my bay windows. The external surface is render and then there is a membrane below this. I was planning on fitting celotex/ kingspan in-between the timbers, taping the joints then putting visqueen/ moisture barrier over this before boarding with 12.5mm board

My questions are:

1) Is this the best way to do this?

2) What thickness of celotex should I used. The timbers are just under 70mm deep, would I be better cramming in 75mm celotex or using 50mm and having a small void between celotex and plasterboard (this might help me to fit my electrical sockets in the wall too actually).

3) How would I insulate the roof space, would it be to just put some rolls of standard loft insulation up there, if so would I be better insulating between the actual roof timbers themselves and visqueen over, or just putting some space roll up sitting on plasterboard?

See pics as my description probably isn't the best.

Upstairs bay ceiling:


Upstairs bay wall:


Downstairs bay wall:



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