foil backed plaster board

[marsaday]

What do you think i should do in my loft conversion. there will be celotex under the rafter and this will be taped up, so making a decent VB.

To be sure of a good VB i want to either add a polythene sheet under the celotex and add the plaster board OR not use a polythene sheet and use foil backed plaster board.

What would be best. any other comments ?

 

[noseall]

I always use duplex (foil back) plasterboards. It is the simplest and cheapest way to install a v.b.

 

[marsaday]

great, so these combined with the celotex taped up will be ok then.

does the same apply to the gable walls be insulated? i am using 50mm between the studs and then 50mm over them.

 

[PrenticeBoyofDerry]

I always use duplex (foil back) plasterboards. It is the simplest and cheapest way to install a v.b.

Me too! great product ceilings and walls
do the gables the same if they are not or you don't intend to cavity fill.

http://www.insulation.kingspan.com/uk/pdf/tw55.pdf

 

[noseall]

great, so these combined with the celotex taped up will be ok then.

does the same apply to the gable walls be insulated? i am using 50mm between the studs and then 50mm over them.

Yup. I like the belt and braces idea of foil tape to all joins too. 'Tis the way i do it.

The idea is to keep all the moist warm air on the warm side of the insulation, not allowing one breath of air to meet the the cold side and subsequently condense.

 

[Deluks]

Either or but not both.
Polythene is cheaper, but slightly fiddlier.
You can buy vapour barrier on a roll, 50sqm for about £15 - £20