Warm flat roof meets cold pitched roof VCL / insulation help

31 May 2023
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United Kingdom
Hi, help and advice needed.

Recently moved into a 1960 as built dormer roof / pitched roof house. Bloody freezing !. Found only 25mm insulation under the boarding in the pitched roof loft and only 25mm in the dormer flat roofs. Both open to each other via the 200mm roof / ceiling joists. No sign of an vapour control layer.
My plan is to strip the flat roofs and insulate as a warm roof and insulate / vent the pitched roof as a cold. My concern is around the junction of both and how to cross insulate and the correct line of vapour control.
Hopefully my pictures and drawings make this more clear.
As usual, any guidance and help gratefully received.


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I must admit that is an option to consider. I would still need to open up the flat roofs from above to get the insulation in between the joists and leave the air gap for cross ventilation.
Thanks for the thought.
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Or alternatively EWI entire house and ventilation strategy.

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