27 Aug 2011
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United Kingdom
Hi, I'm in the process of refurbishing a lean-to extension. Originally there was a false ceiling with no insulation at all. I've pulled all of that out and fitted 50mm Celotex between rafters and 62mm insulated plasterboard under rafters (so another 50mm insulation + the 12mm plasterboard). Total insulation is now 100mm and greatly improved from previously.

I've just had a builder in to look at some work i've asked him to carry out and he's mentioned that the building inspector will be looking for 125mm insulation in the roof space and could ask us to improve what I've done. Is this right? I'm starting to get really annoyed with the regs...if i hadn't done anything the extension would have no insulation yet would be ok! go figure!

Any advice and help very very welcome.
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The figure of 125mm is about right for a lean-to roof, but why bother about it?
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Then don't bring it to his attention. If he specifically asks about it, then you're not that much below the standard, and most inspectors would take a view on it and let it go.

If the worst comes to the worst and he is insistent on following regs to the letter, see if you can put additional insulation elsewhere to compensate; or have you, for example, got smaller windows than would normally be allowed?

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