Conservatory Roof Insulation

18 Aug 2021
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United Kingdom
I've moved into a place with a first floor (don’t ask) 3m x 6m conservatory. It’s brick/breeze block up to the timber windows which are double glazed in a timber structure up to the timber rafters. It’s got a polycarbonate roof.

My problem is the usual one with conservatories – being either too hot or too cold. I was looking to replace the whole thing with an aluminium framed glass version but, on investigation, it turns out that the foundations are only 20cm deep (as approved in the original planning permission 20 years ago) which wouldn’t take the extra weight. I can’t afford to knock both floors down, put in new foundations and rebuild. The current structure still appears to be sound after all this time.

So I was looking for an insulation and ceiling cover solution that didn’t add significant weight to the existing framework. As it was leaking and I needed a fast lightweight fix I’ve just replaced the polycarbonate roof like for like so I’ll need to keep that now.

The lean-to roof drops from 2.4m to just under 2m front to back. Any overall solution thicker than 3cm from the underside of the rafter would not only make the lowest ceiling height even more unacceptable but would also cover the top of the window frames.

The necessary air gaps around foil insulation made that too thick and ruled that out so I checked out ‘between rafter’ insulation and thin cladding over that. Any combination of Kingspan type boards and lightweight UPVC cladding didn’t seem to be particularly fire safe to me – even though the current timber frames would probably burn very well just by themselves.

I’m going round in circles with loose insulation, insulation foils, fire boards, cladding, etc. but can’t find a good solution that satisfies my requirements on thickness, weight and fire safety. I don’t know if there is an ideal solution but I’d really appreciate any suggestions.
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