warm pitched roof detail - ventilation

[garyo]

Hi,

I'm building a warm roof as per the diagram below - with a 50mm ventilation gap between the membrane and insulation. Given that I'm using a breathable membrane, am I right in thinking that I don't need over fascia vents?

I'll foil tape the PIR insulation together to form a vapor barrier between the room and the roof.

Untitled

• garyo
• 13 May 2013
• 1

Thanks

Gary

 

[freddiemercurystwin]

Yes.

 

[tony1851]

Isn't that a cold roof?

 

[hardmetalking]

A warm roof does not have any ventilation!

Any small "voids" in a warm roof are areas of risk where condensation can occur, no matter how small.

What you're describing is a cold roof.

 

[^woody^]

Whether vents are required, will depend on the actual membrane and the conditions of installation set out in the BBA certificate, or manufacturers guidance.

And yes, its a cold roof

 

[garyo]

I did wonder... I'll check out the membrane data sheet. It's a Tyvek something or other.

 

[flatthumbs]

My understanding is your proposed detail is a ventilated warm pitch.
warm pitch can be either ventilated or non-ventilated depending upon barrier systems used. Insulation can be above, inbetween or partially between & below the rafters to constitute a warm pitch roof.

I suspect though, you should be using an impermeable barrier beneath the roof tiles with a 50mm ventilated void beneath. Eaves and ridge vents would likely be required. As mentioned previously check with the manufacturer for their recommendations and construction details etc. There are some good details available from people like kingspan that show a few variations of constrcution make-up etc.

The alternative is a non ventilated detail whereby you have a vapour permeable (breather) membrane beneath the tiles, insulation sandwich, then a vapour control layer and finally plasterboard.

 

[tony1851]

My understanding is your proposed detail is a ventilated warm pitch.
warm pitch can be either ventilated or non-ventilated depending upon barrier systems used. Insulation can be above, inbetween or partially between & below the rafters to constitute a warm pitch roof.

I suspect though, you should be using an impermeable barrier beneath the roof tiles with a 50mm ventilated void beneath. Eaves and ridge vents would likely be required. As mentioned previously check with the manufacturer for their recommendations and construction details etc. There are some good details available from people like kingspan that show a few variations of constrcution make-up etc.

The alternative is a non ventilated detail whereby you have a vapour permeable (breather) membrane beneath the tiles, insulation sandwich, then a vapour control layer and finally plasterboard.

Pinenot no. 2?

 

[^woody^]

Must be some sort of relative. Unless what pinenot has is contagious

 

[flatthumbs]

Must be some sort of relative. Unless what pinenot has is contagious

Ouch gents, a bit harsh isn't it?

 

[barnaclebill1]

Mmm, well my building inspector told me breather membranes only lets moisture out as they don't breath per se. He said warm roof still need some ventilation due to sweating so i've installed a continuous vent in the soffit?

 

[tony1851]

Mmm, well my building inspector told me breather membranes only lets moisture out as they don't breath per se. He said warm roof still need some ventilation due to sweating so i've installed a continuous vent in the soffit?

'Sweating'? Never heard of that one. One of the advantages of a warm roof is that it solves the ventilation problem.

 

[catlad]

Erm make your mind up Tony you said it was a cold roof earlier in the post.

 

[tony1851]

Erm make your mind up Tony you said it was a cold roof earlier in the post.

doh......