On 30 Oct, 13:14, Mike wrote:

With regard to the walls, *the studs will probably be 89 x 38 CLS on a
600mm spacing with 12mm ply on the inner wall. The insulation will be
75mm foil covered celotex, with a tyvek outer breather layer and fibre
cement weatherboard on the outside to try and make it meet fire regs
(class 0)

Do I need a vapour barrier behind the inner ply?

Do I leave the gap caused by the difference in wall stud depth and
insulation depth on the hot side next to the ply or on the cold side
towards the tyvek or doesn't it matter?


Pretty much what I did except I used ship lap for the cladding mounted
on 2x1 batten nailed to the studs with the building paper held to the
studs by the battens. This gives ventilation behind the ship lap.

I had the gap due to the wall insulation nearest the outside with the
foil side out (only one side of mine is foil covered). Then a poly
membrane which I am told is not strictly necessary but I did it anyway
and the 12mm ply. It worked really well.

I also have a warm deck roof constructed with 105 mm tissue faced
kingspan and a three layer built up felt roof on top. Saves having to
ventilate the roof space.

I have no idea about the class 0 fire regs I am afraid but wait for
others comments with interest.


Andy