Celotex Air Gap in walls and advice on downlighter

[leevis]

Hi
I need to install 50mm Celotex between studs on my extension block walls (single skin). Do i need to leave an air gap?

I can't seem to be able to find stud work timber at 50mm so was wondering a) if i needed to find some (I'm sure there is some somewhere) or should i get 63mm and leave an air gap between the wall and the celotex or just a gap between the Celotex and the plasterboard.

Its foil backed.

Second question, i need to put 200mm Celotex in the ceiling which is going to be a bit of a nightmare as we are wanting to have downlighters installed. Whats the normal process here? Do i install the Celotex flush with the bottom of the roof trusses (if i do this i could make a hole roughly for where the downlighters are going to go) or do i install the whole lot with a gap of 60mm as that is the height of the lights? This gap should hopefully allow for the lights to be placed and enough space to get the power to them.

Trusses are only 90mm high thinking about it so would it be better to put the Celotex on top of the trusses?

I can do this either way but foresee issues with getting the power to these

Lee

 

[oldbutnotdead]

50mm? Single skin on a habitable room? Who designed that?
And Celotex in the ceiling-again, why? Rockwool is much more cost effective and easier to get airtight

 

[leevis]

Single skin of blocks not bricks

 

[oldbutnotdead]

Single skin of whatever is a compromise you put up with not a design feature.

 

[phatboy]

Why do you need to install it between studs, is dot'n'dab or mechanical fixing not a possibility?

For downlights, get slimline ones, they make them as slim as 12mm now, so they don't interfere with insulation at all.

200mm Celotex in the ceiling sounds very generous.... can you use 200mm of Rockwool to get the result you want, or a combination. COuld save a fortune.