Pitched roof to warm flat roof

mrwood777 · 21 Apr 2019

Hi all

I’m just replacing my poorly ventilated and badly installed flat roof with a new warm roof. On doing this the rafters from the adjoining pitched roof will end up in the voids between the joists (they both sit on the same wall plate). The rafters are insulated between, with no ventilation space between that and the membrane/slates.

Do I need to do anything to block any flow of air/moisture from the rafters into the roof joist voids or leave as is?

Any other advice greatly appreciated. A picture below hopefully explains the general idea/issue

catlad · 21 Apr 2019

Yes if its a warm roof you will need to block the ends.

mrwood777 · 21 Apr 2019

catlad said:
Yes if its a warm roof you will need to block the ends.

Thanks. What would you use to block it off with? Insulation and then vapour barrier?

catlad · 21 Apr 2019

Ideally you need to block the ends using the same material as you have used for the rest of your roof.
Vapour barrier goes at ceiling level.

mrwood777 · 21 Apr 2019

catlad said:
Ideally you need to block the ends using the same material as you have used for the rest of your roof.
Vapour barrier goes at ceiling level.

Ok thanks. Do you mean the insulation? I’m just using rigid celotex type so I’ll cut it to fit the voids snugly if so

noseall · 22 Apr 2019

mrwood777 said:
Ok thanks. Do you mean the insulation? I’m just using rigid celotex type so I’ll cut it to fit the voids snugly if so

Use insulation and foil tape/ex-foam.

mrwood777 · 22 Apr 2019

Perfect, thanks!

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Pitched roof to warm flat roof

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