Warm deck roof: how wall insulation meets roof insulation

IE00 · 12 Sep 2021

We're getting an extension with a warm deck roof and have a question about how the wall needs to meet the roof to have good insulation.

I've attached an image of the build as it is now. As I understand it, in a warm deck roof the wall insulation should meet the roof insulation forming a 'sealed' warm space. With the joists sitting on top of the wall - as shown in the image - is this possible?

I'm concerned too about how the vapour control layer will work in this set up, but thats a bit beyond me right now.

Many thanks for your advice

RandomGrinch · 12 Sep 2021

One example of many:

The roof insulation sits above what your photo shows and the wall insulation will fill the gap between.
The plasterboard with vapour control layer can sit below the joists.
I hope that helps!

Swwils · 12 Sep 2021

ACD Ref: MCI-RF-01

Table K1: E14

IE00 · 12 Sep 2021

Swwils said:
ACD Ref: MCI-RF-01

Table K1: E14

https://xtratherm.com/wp-content/uploads/2018/05/XT-FF-E14-MCI-RF-01-0046-Certificate.pdf

Hi Swwils that seems to show our setup. Thanks!

Is your reading of it that the image I shared will be ok as long as the the space above the wall is stuffed with glass wool insulation?

IE00 · 12 Sep 2021

RandomGrinch said:
One example of many:
View attachment 243953
The roof insulation sits above what your photo shows and the wall insulation will fill the gap between.
The plasterboard with vapour control layer can sit below the joists.
I hope that helps!

Hi RandomGrinch - that drawing is what I was expecting, but our actual building work differs!

Swwils · 12 Sep 2021

I think there is a junction limiting value in the approved documents.

If your deck insulation isn't all of it, the VCL will need to be lower in the stack. That pdf you linked uses FR-ALU.

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Warm deck roof: how wall insulation meets roof insulation

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