Warm or cold roof design for our flat roof?

[Great_scot_selfbuild]

It doesn’t feel like I’m getting very clear advice from our principal designer.

 

Any comments on these options?

 

Thanks in advance.

[Big Jimbo]

At a first glance you will want to consider doing something with the huge void between the ceiling and the underside of the warm roof, where all your expensive heat will exit via the eaves.

[JohnMo]

If you do option A you need insulation above the outside wall insulation to join the wall to roof insulation - otherwise it will leak like a seize.

 

But I would just do option B, but add a 50mm service void to the ceiling with a vapour airtight membrane on bottom of rafter and service batten below then normal plasterboard.

[SBMS]

Have you any parapet walls? We went warm roof - was too difficult to detail ventilation. 

Edited October 29 by SBMS

[Great_scot_selfbuild]

39 minutes ago, JohnMo said:

If you do option A you need insulation above the outside wall insulation to join the wall to roof insulation - otherwise it will leak like a seize.

 

But I would just do option B, but add a 50mm service void to the ceiling with a vapour airtight membrane on bottom of rafter and service batten below then normal plasterboard.

I had wanted to go back to option B, but the flat roof and ventilation gap will be a paint to sort, so I’m thinking the option A - I think it’s just a case of taking the wall insulation up to the top.

 

Worth adding that I only received this warm roof design earlier today (5pm) and haven’t yet had a chance to ask him this question - but it will be with him tomorrow!

[Great_scot_selfbuild]

47 minutes ago, SBMS said:

Have you any parapet walls? We went warm roof - was too difficult to detail ventilation. 

Do you mean upstand above the flat roof? If so, there will be a lip of some sort for the guttering. With your warm roof, did you just take the wall insulation up to the underside of the roof board (rather than this drawing showing it stopping at the underside of the joists)?

[SBMS]

2 minutes ago, Great_scot_selfbuild said:

Do you mean upstand above the flat roof? If so, there will be a lip of some sort for the guttering. With your warm roof, did you just take the wall insulation up to the underside of the roof board (rather than this drawing showing it stopping at the underside of the joists)?

We had a parapet wall so the cavity wall continued up past the edge of the roof.