Loft insulation in garage ceiling.

[glangri2]

I need to insulate the suspended floor between the garage and the bedrooms above.

The joists ar 220mm deep so there is plenty of room for insulation.

The floor area is roughly 21 m sq.

I could fit 100mm celotex in the voids, or for significantly less money I could get 200mm loft insulation in there.
(Wickes are doing 200mm loft insulation for what works out at £2.08 per m sq ) and so for about £50 I could stuff the floor full of it.

100mm Celotex will work out at about 6 times that !

I know that I would need a waterproof membrane if I went for the loft insulation, but I guess my real question is will 200mm of loft insulation offer enough of a thermal barrier.


Maybe the best overall plan would be 200mm of loft insulation in the voids, and then 25mm or 40mm Celotex under the rafters. That would cost about half as much as just going for 100mm of Celotex.

I don't mind paying for the more expensive insulation, if there is a definite advantage, but I am keen to save as much money as possible at the same time.

Any advice will be gladly received.

Cheers
Gary

 

[^woody^]

200 quilt will do thermally, but it also has to perform as acoustic insulation. So if it is Rockwool then it will be fine, if not then you need acoustic insulation as well

I don't know why you think that you need a waterproof membrane?

Don't forget the ceiling needs to be double boarded with staggered joints and intumescent perimeter seal

 

[glangri2]

I don't know why you think that you need a waterproof membrane?

I thought that I had read that somewhere. Maybe I am wrong !

Don't forget the ceiling needs to be double boarded with staggered joints and intumescent perimeter seal

Yep, it has to be fireproof, so I was planning on a double skin of 12.5 plaster boards, and 22mm chipbpoard for the floor above.


Being a garage, I am going to use flourescent strips for lighting, so the cabling up in the ceiling void will be minimal.

 

[glangri2]

BCO was happy with the idea of 200m loft insulation.
He also said that as long as the ceiling was plaster skimmed up to the edges, he wouldn't insist on an intumescent perimeter seal.