Vapour barrier needed on PIR boards?

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We have stud work erected on a detached garage with foil faces insulation between the battens. We started putting up a vapour barrier, but then realised whether it was needed at all.

Does the foil face itself act as a VB, therefore not needing another one? I can continue with installing the poly sheet but just wondered if its needed at all, or any harm will come with it installed.

See attached

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Does the foil face itself act as a VB, therefore not needing another one?
Are you going to fix another layer of insulation across the studs on the warm side? It certainly needs it and this will provide you with adequate VB as long as you foil tape all the joints on both layers. Fixing duplex boards (warm side) will help too.
 
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There wont be another layer of insulation after this. Just a double layer of plasterboard.

We don't have much floor space and adding another layer didnt leave us with much.
 
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It does come in very thin sheets. The 12.5mm ones would be the same as one of your plasterboard layers and be much easier to tape together to give a VCL.
 
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You can normally just tape foil board insulation for the vcl, and across the timber.

But, you have too many many gaps and they are excessive. No vcl is going to help you there, and you need to remedy those.
 
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You can normally just tape foil board insulation for the vcl, and across the timber.

But, you have too many many gaps and they are excessive. No vcl is going to help you there, and you need to remedy those.

Are you referring to the gaps between the insulation and timber battens? We are using foam or foil tape to cover those.
 
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There wont be another layer of insulation after this. Just a double layer of plasterboard.

We don't have much floor space and adding another layer didnt leave us with much.
A second layer of inso' across the studs prevents any cold bridging through the studs thus preventing the risk of shadowing.
 
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Are you referring to the gaps between the insulation and timber battens? We are using foam or foil tape to cover those.
You can't cover a gap with tape. Any gap is a pocket of air and that presents a condensation risk.
 

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