Double the foil insulation, double the warmth?

[Tom079555]

Perhaps a daft question, but - I've bought some foil thermal insulation. It says that it's the equivalent of 300mm of rockwool.

If I was to put 2 layers on top of each other, would that be the same as 600mm of rockwool, or does it not work like that?

What ive actually done is put 500mm of foam board into a stud wall, and foil insulation on top of that. Do you think the foil will help even more with insulation, or not make a difference?

 

[Doitproper]

The important issue with foil is to provide unventilated air gaps, so a 40mm foil actually occupies about 90mm to take account of the low emissivity surfaces. So 2 lots of foil would need a thickness of 155mm - and gaps should be sealed (unventilated).

 

[noseall]

I've bought some foil thermal insulation.

Chuck it in the skip.

 

[Doitproper]

I was very dubious of it 15 - 20 years ago when some BCO's would accept it but not others. I think now the testing has improved, the theoretical myths scientifically examined and the results better reflect reality. The proper stuff has regulatory approval and needs to be draped over the rafters / studs and requires counter battening. It cant be sandwiched behind the plasterboard.

 

[noseall]

I think now the testing has improved

It's sill the same old faffy, jump-through-hoops, bollax though.

 

[Doitproper]

Can not argue with that, its called progress and unfortunately the "faffy, jump through hoops" culture is here to stay. Its an alternative which has improved over time to now being (IMHO) a robust product. My personal preference for using it is that a service void can be built in behind the plasterboard and the vapour barrier is not destroyed when the electrician installs the ceiling lights. Also, it mitigates any airflow around poorly fitted solid insulation but there again you need to have the laps well sealed..