Hi
In my extension i have a pitched roof with a flat horizontal bit at the top.
I wanted to keep as much height as possible.
The kingspan is 75mm between rafters and 50mm under.
This runs right upto the UB ridge beam and the beam protrudes down, to white 4x2's are fixed touching it horizontally.
The kingspan runs right upto the beam.
I was then going to put 100mm quite roll between the joists and 170 over the top just to fill up this gap.
It would have been much quicker to put 75mm between these 4x2's and 50mm underneath, however i loose 75mm off the height then (with the 2x1 batten) so opted to do it this way.
All joints on the kingspan are taped with foil tape which creates the vapour control layer which is needed.
At the top, the UB itself i suppose will be colder and also breaks the vapour control layer a little. The foil tape goes over the joint with the UB and kingspan.
I know its only a vapour control layer and not a vapour barrier, and all the kingspan is taped etc. Is it worth going over the full lot with a vapour barrier, or possibly even the top flat horizontal part, or is it just wasting time/money?
Also, vapour barriers seem to be 125mu / 500g.
Screwfix do one for £19 but the reviews say its pretty thin.
I know its only polythene, does the specification of it have to be a minimum mu or g?
Can a large roll of black damp proof membrane which is either 250mu / 1000g or 300mu be used instead?
thanks for any help
In my extension i have a pitched roof with a flat horizontal bit at the top.
I wanted to keep as much height as possible.
The kingspan is 75mm between rafters and 50mm under.
This runs right upto the UB ridge beam and the beam protrudes down, to white 4x2's are fixed touching it horizontally.
The kingspan runs right upto the beam.
I was then going to put 100mm quite roll between the joists and 170 over the top just to fill up this gap.
It would have been much quicker to put 75mm between these 4x2's and 50mm underneath, however i loose 75mm off the height then (with the 2x1 batten) so opted to do it this way.
All joints on the kingspan are taped with foil tape which creates the vapour control layer which is needed.
At the top, the UB itself i suppose will be colder and also breaks the vapour control layer a little. The foil tape goes over the joint with the UB and kingspan.
I know its only a vapour control layer and not a vapour barrier, and all the kingspan is taped etc. Is it worth going over the full lot with a vapour barrier, or possibly even the top flat horizontal part, or is it just wasting time/money?
Also, vapour barriers seem to be 125mu / 500g.
Screwfix do one for £19 but the reviews say its pretty thin.
I know its only polythene, does the specification of it have to be a minimum mu or g?
Can a large roll of black damp proof membrane which is either 250mu / 1000g or 300mu be used instead?
thanks for any help
