Hybrid flat roof design in dormer window

[garyo]

Hi,

I'm planning on building a 1500mm wide dormer window into a 45 degree pitched roof. I'm at the 'design' stage and rather than going for cold/warm roof, I want to go for hybrid for space reasons. Is this likely to be a can of worms for the BCO, or has the world grown more tolerant of this approach?

I'd like to take the same approach with the walls: 100mm deep full-fill PIR between joists pushed tight up against the outer skin, and then a continuous 50mm PIR over the top - no air gaps. Does that seem feasible?

Thanks

Gary

 

[Notch7]

My understanding is that hybrid roofs are tricky to form a vapour barrier and so insulation manufacturers arent keen on doing condensation risk analysis given so much depends on workmanship and lots of potential variants.

I personally think if a reasonable amount of insulation, say min 50mm is over the top, then the risk isnt too great.

Ive not seen BCO fuss too much -they cant see all the detailing anyway.

 

[^woody^]

It worked on my house

 

[garyo]

Thanks. I think I might do it on a full plans submission anyway, so I'll have a chance to haggle before the point of no return is reached. It's so small that there shouldn't be any joints in the 50mm sheets that I use for the walls and roof, so I feel pretty comfortable with the approach anyway.

 

[Notch7]

Thanks. I think I might do it on a full plans submission anyway, so I'll have a chance to haggle before the point of no return is reached. It's so small that there shouldn't be any joints in the 50mm sheets that I use for the walls and roof, so I feel pretty comfortable with the approach anyway.

I had meant to include this link
https://www.ealconsult.com/warm-roofs-go-wrong/