Has there been a mistake made here?

[thomp1983]

Hi,

I'm on putting PIR board into the pitched roof part of our extension but I've some concerns.

Looking at my woodyesque drawing above, the airflow travels through the soffits at the front, up and down the pitched roof above the PIR boards but then vents out into the flat roof of the kitchen under the warm roof so in the void between the kitchen ceiling and the osb below the warm roof insulation.

Surely this is just going to make the kitchen cold and defeats the point of the kitchen having a warm roof or am I worrying about nothing?

The front soffits aren't fitted at the minute so there's alot of airflow up and over the PIR board, I suppose this will reduce quite a bit once soffits are in and gaps sealed.

Thanks
Chris

 

[RonnyRaygun]

If you use a breathable membrane beneath the tiles you don't need vents.

 

[freddiemercurystwin]

 

[thomp1983]

There is indeed breathable membrane below the tiles, so does that mean I don't need to worry about it?

 

[freddiemercurystwin]

In theory, if the breathable membrane is suitable/has been installed correctly. That said you can't beat natural ventilation whatever the membrane.

 

[^woody^]

It depends what breather membrane it is, and whether it certified for use without additional ventilation.

You would not want your ventilation running under the insulation on the flat roof. What would the insulation be insulating?

 

[catlad]

It depends what breather membrane it is, and whether it certified for use without additional ventilation.

You would not want your ventilation running under the insulation on the flat roof. What would the insulation be insulating?

Lol. I distinctly remember You telling this forum that all membranes were all the same! I think it was saturday night though!

 

[catlad]

Good to see you have been learning

 

[Notch7]

warm roof abutment to cold roof -pitched tiles -commonly done wrong, Ive seen builders do it wrong...

 

[Notch7]

Good to see you have been learning

that'll go down well with Mr Happy

 

[RonnyRaygun]

He’s been on the Technical Index reading up on research papers

 

[catlad]

that'll go down well with Mr Happy

Its alright by the time he has read this he will be on his second bottle of plonk!

 

[thomp1983]

So what do I do then? I can block the end of the pitched roof where it vents under the warm roof with rockwool but then I assume I'll need some vented tiles on that side of the pitch?

 

[^woody^]

Lol. I distinctly remember You telling this forum that all membranes were all the same! I think it was saturday night though!

Are you sure it wasn't "chow meins are all the same"?

 

[catlad]

You need to block it off with the same insulation as your warm roof.
You don't need any tile vents, you can use over fascia vents on the first row of tiles above the flat roof.