It’s now nearly a year since the two most important building control bodies in the UK moved to stop the use of multifoils, at least as a substitute for conventional insulation materials. Under pressure from government, the LABC (Local Authority Building Control) and the NHBC (National Housebuilders Council) simultaneously stated that in future they would only accept insulation that met the standards laid out in BR443, which translates as using the U value figures derived from the guarded hot box test.
Multifoil insulation performs very poorly in guarded hot box testing. The manufacturers claim that it’s the guarded hot box test which is at fault. Their case rests on them performing well in comparison tests against conventional insulation, usually 200mm or 250mm of mineral wool. Such tests have been carried out several times by the multifoil manufacturers, to the satisfaction of some independent accreditation providers, but they have yet to win a European Technical Approval for their testing methods and they remain highly controversial.
I don’t want to dig too deeply down into the multifoil debate here — it has been covered several times on this blog already — but what is worth mentioning at this point in time is that there are still a number of private building control bodies out there who are more than happy to accept multifoil roof insulation. I was talking to a director of MLM last week and he remains an enthusiastic supporter of multifoils and is more than happy to sign off building works that use multifoil insulation. And I came away with the impression that MLM are far from unique in this respect, and that private building control saw this as a positive way of differentiating their services from the strictures of both local authority building control and the NHBC.