Mike Garnham":uxfj8f11 said:
BigShot":uxfj8f11 said:
Kinda makes it clear just how mad the insulation regulations for houses are. Foil membranes, for example, are cheaper and easier to fit than anything that meets the official requirements - but they do a perfectly good job. Once things are "warm enough" in the dead of winter - anything else is just overkill!
No no no!!!!!!!
Granted there is a law of diminishing returns at play with insulation depth (ie the first inch of insulation when you have none at all does an awful lot more for the thermal efficiency of a building than, say an extra inch when you already have 12), but more and more insulation means less and less fuel. End of story.
There is a line, yes, but I believe it is drawn in the wrong place. The level of insulation put into loft conversions is, in most situations I deal with, far more than is needed. When you're working with a limited space, like in lofts or in this case sheds for small workshops, the extra thickness of insulation eats right into your usable space... It's not simply a matter of how much fuel is needed, though that's a factor, it also affects the physical size of the rooms in question - something that is all too often overlooked (to the point where people will, and do, have loft conversions done without building regulations approval because authorities are insisting on insulation so thick it makes a tight job impossible).
The point, though, is that foil membranes have been in use all over Europe for 20-odd years (IIRC) and do a perfectly good job of keeping things "warm enough" even up in the alps. I lived in a swiss-style chalet in Chamonix for a while and even when things were sub zero outside we didn't use the heating. The sloping roof (with no ceilings at first floor and no first floor at all in parts) was insulated with multi-foil insulation only.
Secondly, they are having difficulty proving that they work.
I dunno about that... They are having difficulty proving that they work when tested in a completely unrealistic test. A test which takes no account whatsoever of external conditions. Houses, sheds, workshops, loft conversions and alpine ski lodges are never built in hot boxes.
Real world tests of Tri-Iso Super 9 have indicated fuel use equivalent to 200mm of fibreglass insulation in similar situations - and Super 10 (double the thickness) only makes things better.
Thirdly, in rooves they require additional insulation to reach the min. requirements of Part L of the regs.
I acknowledged in an earlier post that the foils don't meet regs alone - though that may be more a regs problem than a product one. See also above comment about inadequate and unrealistic testing.
I'm unconvinced that the min. requirements are entirely sensible. When you've stood in a loft, in the dead of winter, with no heating and comfortable inside temperatures and you KNOW the insulation doesn't meet requirements it says a lot about the requirements. It's only anecdotal, but it makes a difference in the real world.
Roofs are another reason foils are a good idea and at times a better idea than other insulants. In a small workshop and even more so under a sloping roof in a loft conversion, the extra space taken up by foam insulation can have a critical impact on available space inside the room.
All that said, I agree completely that an air-gap is necessary. For warmth squashed in glass seems to do the trick for a shed (going on anecdotal evidence in this thread) but as I said in an earlier post, ventillation (air gaps in non-"warm deck" construction) needed looking into.
(This'll be marked as edited, nothing more than correcting a formatting error)