Insulating rafters without ventilation

[Martin Pentreath]

Hi,

I've been umming and ahhing about putting kingspan/celotex between the rafters of my loft to beef up the insulation. I can't get insulation between the celing joists because most of the loft is boarded for storage.

I got put off by the problems of making sure there was enough ventilation on the cold side of the insulation to stop the rafters rotting. A friend has just put me onto this website - he used the stuff for a loft conversion recently, and said it was accepted (reluctantly) by the BCO:

seems to be basically a vapour barrier which gives a bit of insulation of its own by being made of bubble wrap and tin foil. It's used in conjunction with celotex. They try to get round being tarred with the multi-foil brush by saying: "Alreflex products are "bubble sheet with aluminium foil facing" as categorised under BR443 paragraph

3.10.1. They are NOT the "multi-foil insulation" referred to under paragraph 3.10.2."

Any thoughts on this?

Cheers!

Martin

[Hugo Nebula]

On Wed, 29 Aug 2007 10:46:35 -0700, a particular chimpanzee, Martin Pentreath randomly hit the keyboard and produced:

Yes, it's lies.

The underlying principle that a high-emissivity material will give a higher thermal resistance is understood and accepted, but this only applies where there is no ventilation or air movement. A loft is subject to a lot of air movement simply by being a large open space; the upper side also needs ventilation, as the material is NOT vapour-permeable. The BS for ventilation (ICBA to look it up) basically says that vapour barriers cannot be relied on to keep out all moisture, and that some form of ventilation IS required (either via eaves and high level vents or a vapour permeable membrane).

It has no BBA Certification for anything other than cavity insulation. It's about as good as one would expect bubble-wrap painted silver to be.