Insulation positioning

[thomp1983]

Hi all,

Quick couple of questions about insulating my extension.

1, I'm using 150mm celotex between the roof trusses, do I push the board up tight to the felt and leave the air gap between the plasterboard and insulation or leave the insulation flush with the bottom of the trusses so the air gap is between the board and felt and the plasterboard is touching the celotex?

2, The existing single garage is becoming part of a bedroom, the external wall is single skin brick, bco says I need 100cm celotex for that wall, do I fit visqueen against the brickwork then the celotex or the celotex to brick then visqueen?

Do I need to batten the single skin to create an air gap before the above visqueen/celotex?

Thanks
Chris

 

[cwhaley]

For insulation in the ceiling (between rafters/joists) the air gap needs to be between the underside of the felt and the top of the rigid PIR. The minimum gap is 25mm.

For the external wall insulation, it should go brick>membrane>insulation>plasterboard. Don't leave a gap between insulation and the wall.

 

[Diybeginner5]

For insulation in the ceiling (between rafters/joists) the air gap needs to be between the underside of the felt and the top of the rigid PIR. The minimum gap is 25mm.

For the external wall insulation, it should go brick>membrane>insulation>plasterboard. Don't leave a gap between insulation and the wall.

Hi I’m looking to insulate a wall like this and someone on my thread suggested no membrane was needed if the insulation was flush to the wall and taped and sealed. Is this not the case and if so I’d be grateful for a link to whatever membrane I need to use? Many thanks!