Low pitch roof with vaulted ceiling - ventilation or not?

15 Oct 2016
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United Kingdom

Looking for some advice. There seems to be 2 schools of though concerning ventilation on a low pitch roof for my extension. The room adjoins the kitchen area (semi open plan)

The roof is 15.8% and standard cold roof construction. No joists with rafters spanning 3.7m at less than 400 centres (building control ok'ed) and one velux. I will be using a marley fibre cement rated for the pitch. For clarity- this is a vaulted ceiling will 100mm celotex, airgap + 25mm + foil backed board

Ref ventilation: I am told that if you minimize air gaps as much as possible with insulation etc then there is no need to ventilate the roof. The alternative is to use eaves vent kit with a wall abutment vent kit (low profile).

The vents do not particularly cost a lot or really add a lot of time for fitting but I am keen to get it done the in the right way that does not come back to haunt you with problems.

Thoughts welcome

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Who told you you don't need ventilation? There aren't two schools of thought, you don't need to ventilate if the insulation is above the rafters otherwise you do. And why have you got a gap between the insulation?
The non-ventilation offering came from a builder who specializes in green/environmental work. Ref the gap, the BC officer insisted on it, plus, the rafter width kind of dictated it.

I also scratched my head after a roofer who quoted for the job looked puzzled when I mentioned the use of abutment ventilation.

Thanks for the comments

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