Warm Roof to Cold UNVENTILATED Roof Detail Junction

[BartW]

Hi All,

 

Looking for some knowledge, and reassurance that the below will fly:

 

 

 

Building Control so far happy with the detail, but I want to ensure there is nothing that will later be stipulated as a bad practice, etc.

 

I know all cold roofs have to be ventilated, but even if I propose a full fill there?

 

 

It is a funny junction of the two roofs, and lack of ability to create a cold roof ventilation.

 

3D model below:

 

 

 

 

 

Your feedback would be most helpful!

 

 

Thanks

Bart

 

 

 

 

 

[Russell griffiths]

Your drawings don’t mention a vapour control layer, you need to prevent moisture entering the roof structure. 

[Gus Potter]

I think there may a be a good bit missing from this detail.

 

How are the sloping rafters supported, how do you stop moisture passing through the warm roof ceiling and into the sloping part?

 

I think this needs much more thought. I have a similar detail on my own house and it took a lot of thought to get it to work. It's also quite labour intensive to construct.

 

I have ended up with a warm flat roof. The sloping roof is full filled, insulated plasterboard to under side with supplementary vapour barrier. They key for me was to adopt a two pronged approach to the sloping roof. On the sloping roof I used timber sarking with a breathable membrane, counter battens, battens and concrete tiles. The soffit is vented and at the top the roof membrane overhangs the sloping roof with a concealed vent to allow the sloping roof to vent, like a mono pitch roof abutment vent.

 

Basically I decoupled the two types of construction so that the warm roof membrane sheds the water onto a sloping abutment roof. If you look at some of the Marley details they will help, just pretend (it is Easter after all) that the abutment wall is your flat roof.

 

Hope this helps.

 

 

 

[BartW]

On 05/04/2021 at 21:28, Gus Potter said:

I think this needs much more thought. I have a similar detail on my own house and it took a lot of thought to get it to work. It's also quite labour intensive to construct.

 

Hi, have you got a detail to hand? BC signed it off, but I want to avoid having to go back later on in case there is a change of mind. 

 

Warm to Warm was a previous idea, but then I would be loosing quite a bit of volume in the attic, as would need to shift rafters down by 150mm. The basic idea here is that by the time I install the solar pv on top the two roofs should almost marry up height wise. There will be timber cladding on that part of the roof too.

 

 

 

On 05/04/2021 at 21:25, Russell griffiths said:

Your drawings don’t mention a vapour control layer, you need to prevent moisture entering the roof structure. 

 

Yes, I omitted it when I was doing a quick sketch, but needs to be added of course.