Warm roof insulation

[hoyjoh]

I have just purchased Celotex WR4000 150mm thick and plan to put this between the rafters in a new extension, I would then like to leave a 50mm gap from the Celotex to the underside of the rafters, with Celotex PL4025 fixed to the rafters underneath. The 50mm gap will provide me with a gap for cable runs etc for lighting and also provide a sufficient void for ceiling spotlights to fit.

Is the 50mm gap between the XR4000 and the PL4025 acceptable and conform to regulations or should there be no gap at all between the two?

 

[^woody^]

There should be no gap unless its vented from end to end

 

[pred]

Are you talking of a flat roof?

 

[^woody^]

Flat roofs don't have rafters

 

[pred]

On a flat roof installation a warm roof requires you have an air gap.

This was the only time I heard the phrase "warm roof" that's why I asked.

 

[^woody^]

On a flat roof installation a warm roof requires you have an air gap.

No, that is incorrect

 

[pred]

On a flat roof installation a warm roof requires you have an air gap.

No, that is incorrect

Are you sure about that?

https://www.google.co.uk/search?q=flat+roof+warm+deck&tbm=isch&
tbo=u&source=univ&sa=X&ei=PlG2Ucz8G87EPOezgIgO&ved=0CFIQsAQ&
biw=1266&bih=881#facrc=_&imgrc=hr-sVRu1u6GL_M
%3A%3BP4HpHDUpE_nxTM%3Bhttp%253A%252F%252Fwww.arrowroofing.i
m%252Fimages%252Fjpg%252FInformation%252FWarm_Roof_FlatRoof_L.p
ng%3Bhttp%253A%252F%252Fwww.arrowroofing.im%252FInformation_
Roofing_Terminology_Flat_WarmRoof.html%3B800%3B600

 

[freddiemercurystwin]

Pred, this is a little embarrassing. The clue is in the name: warm roof!

Educate yourself man: http://www.delston.co.uk/coldvwarmroof.htm

 

[pred]

I was told by the architech that I had to maintain the air gap between the roof boards and the plasterboard to ensure it was a warm roof, I wanted to save room and put the Celotex between the joist but he assured me this would make it a cold roof.

 

[freddiemercurystwin]

He was clearly on drugs.

 

[Walkbar]

I was told by the architech that I had to maintain the air gap between the roof boards and the plasterboard to ensure it was a warm roof, I wanted to save room and put the Celotex between the joist but he assured me this would make it a cold roof.

There's the space between the plasterboard and the roofing board fitted top and bottom of the joists. The warm roof insulation and capping is on top of that without air gaps.
I take it that's what you mean, so no-one is on drugs in this instant.

 

[noseall]

A warm roof is not vented.

A warm roof does not have an air gap.

A warm has the insulation wholly above the rafters not between.

 

[limerockconstruction]

A warm roof is not vented.

A warm roof does not have an air gap.

A warm has the insulation wholly above the rafters not between.

I concur.

Warm = no gap. The entire deck is made up on top of the joists stacked one on top of the other, ply insulation, deck and roof covering.

Air gaps and insulation between are indicative of its brother the cold roof, which brings you into tricky ventilation territory.