Flat to pitched warm roof detail

[BartW]

Hi again,

Sounds like there will be a lot more of me seeking reassurances going forward....

 

 

I have two roofs adjoining:

- warm flat 

- warm pitched

 

Detailed as below:

 

 

 

Can anyone see problems with it?

 

It was going to be warm to cold initially, but possible cold bridges and likelihood of failing in such form had me redesign it. Or would an inverted hybrid be better on pitch? i.e. 60mm over the joists, and 60mm inbetween?

 

Thanks!

 

 

 

 

 

 

 

 

 

 

[Iceverge]

Have you planned a fall for your flat roof? Bregs suggest 1:40. 

[BartW]

3 minutes ago, Iceverge said:

Have you planned a fall for your flat roof? Bregs suggest 1:40. 

 

Yes, falls towards the pitched roof.

 

 

[BartW]

Thinking about this again, would I be able to achieve better performance of the pitched roof by doing a 100mm PIR above rafters, and 100mm rock wool between the rafters? Decrement delay and thermal mass come to mind, having read a few recent posts.

 

Also, would it fly with flat "warm roofs"? I.e. 100mm PIR above, and 100mm rock wool between rafters?

 

[BartW]

Anyone to comment please?

 

Also, weirdly, Kingspan suggest 60 over + 60 in-between for the "warm" roof buildup on pitched.

 

Any benefit to having sarking vs no sarking?

 

Would I be better off doing that instead of bulky 150?

 

 

[Dave Jones]

no vapour control barrier shown on the drawings, absolutely critical. Alutrix is the best.

 

Look at kingspan thermataper insulation, you can adhere EDPM directly to it saving the cost of 1 layer of decking.