I'm planning on building a new large shed, hopefully with low heating
requirements and a steady temperature all year round to enable me to
use it for woodworking projects.

To keep the heat loss down to a minimum I'm going to use a high level
of insulation in the walls floor and ceiling but even after reading a
load of literature. I can't work out if what I'm doing is going to be
ok.

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?

The shed will be around 0.5m from a shared boundary fence and at least
5m from any existing structures. Will a mainly timber frame structure
covered in fibre cement weatherboarding (with a green roof of sedums)
meet class 0 standards or will I need plasterboard on all the inner
surfaces?


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