timber frame insualtion and vapour check

26 Mar 2020
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United Kingdom
Timber Frame annexe has cladding, battens, breather membrane, OSB, then 150mm timber frame wall

celotex between studs

Then what's my best option as regards insulating, vapour barrier , service voids etc

A multi foil insulting vapor barrier seems a good idea ???

If constructing internal stud walls, where they start from the outer frame , presumably they want fixing / butted up over the vapour / insulating layer?
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Multi foil is very tricky to get right in those situations. I would infill around services with PIR and fill any gaps with foam.
Insulation and vapour barrier should be continuous behind wall junctions.
If the frame is already insulated, what is the question about insulation for?
If adding more insulation to an insulated frame, then you really should use the same insulation and definitely not introduce a void, or or use something like multifoil

Ideally, services should be on the inside of the vapour layer. Otherwise just detailed (and enclosed) into the frame and insulation and not with a concept of a "service void" unless you are actually designing a proper service duct for all the services to use.
Apologies , for confusing things. I will put celotex between timbers, before plasterboard i believe i have to put a vapour barrier or foil backed plasterboard.
Im trying to avoid the cold bridging on timbers. I thought multi foil was ok as long as you had air gap one side. Therefore i thought it would achieve the vapour barrier and take care of the bridging.
Id also have battens then p/board to finish which would create a gap for electrics , pipes etc.rather then penetrate the insulation & v/barrier behind?
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Put a layer of Celotex across the frame, tape the joints and that's your vapour barrier. Services can be set into this and taped over, but if you are battening before boarding that will created your void.

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