Flat Roof ventilation

9 Sep 2008
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United Kingdom
I am insulating the walls and ceiling of a 6m x 3m breezeblock construction outbuilding for my father in law in Scotland that has a flat roof with previously no insulation and no soffits. The roof just covers the width if the walls with no overhang. It has double glazed windows and door.

We will need to insulate the ceiling to make a cold roof with a 50mm air gap from the top of the insulation to the underside of the roof.
I will be aiming to fit as good a vapour barrier as possible in the ceiling below the insulation that will link up with a vapour barrier over the wall insulation.

I do feel that we need to ventilate the 50mm air gap.

The roof is watertight so I am loathe to put in 10 mushroom vents.... ie one for each bay between rafters.

If there are no soffits what is the best way to ventilate between the rafters through the side of the building. Can we just drill a series of holes and put simple louvre vents over them behind the guttering?

Thanks for any advice.


Tommy Banana
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