garage conversion insulating loft

[matz]

in doing an intergrale garage conversion I now have to insulate the loft.

According to building control, if using celotex I have to place 70mm between joists with 80mm on top. I aim to use 60mm between joists with 90mm on top as I dont want to risk the plasterboard ceiling pressing down as a result of storing stuff in the loft area when completed. (the joists are 70mm deep)

My question - given I am laying 90mm celotex across the whole lot, how good a fit do I have to make the 60mm between the joists. Obviously the looser it is the quicker the job. is the buliding inspector really going to pull back the top layer of celotex to see whats underneath and how well its fitted?

 

[freddiemercurystwin]

Well they should be tight enough to hold or pop a couple of nails in at the bottom of the joists and press the insulation onto them. you should be filling the gaps with expanding foam anyway so not too important. Any gaps left will just reduce the effectiveness of the insulation which seems a shame given the expense and overall effort of a garage conversion.

 

[matz]

what about Warmcell100? I have read about this product whereby the loft spaces are loose filled. So if I did that to the top of the joists then laid 90mm celotex across the top, would this suffice?

well if my calculations are correct, if I use 60mm of warmcell100 between the joists (U value 0.50) I need to lay 105mm of celotex across the top. Sounds like thats easier than cutting up dozens of small pieces of celotex.

but now according to Warmcell, the mixture of types will cause problems so its back to the celotex pieces