u ratings - 3.6N Aerated Celcon versus 50mm Cellotex

30 Mar 2012
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United Kingdom
I have a car port under the end of the house, the supports for the house are conc. blockwork, L shaped (in section) piers with a 2" cavity containing Rockwool or similar insulation. The car port is being converted to domestic/internal room.

BC says that original internal faces of car port piers need 50mm of insulation to achieve necessary u value, but I'd be happier just hiding them behind a standard 100 thick aerated Celcon/Thermalite wall (I don't mind losing the extra 50mm of space). I don't like stud walls and avoid them like the plague.

Is this likely to be acceptable? Will 100mm aerated blocks boost the u value as much as 50mm Cellotex?


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On my spectrum of things to avoid, it goes stud walls, then 500mm thick walls, and then the plague.
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Have you considered "glueing" celotex bonded plasterboard on? Will feel a bit more solid than a stud wall.
My list of things to avoid usually puts things that I can't do at the top.

Dot'n'Dab - I won't be able to do that.

Would a 50x75 (63 deep) CLS frame be ok? With 50thk Cellotex inserts. Faced with 12mm plasterboard. Only 12mm behind the boards for cables though.

Or maybe 100mm CLS (89 deep) would be more rigid, with more room behind the Cellotex for running cables.

@ what maximum ctrs?

Presumably I need a wider landing where the vertical edges of 2 boards meet, than the 38 wide edge of the CLS?
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So, a 4" deep stud would let me run any pairs of socket cables well back from the face. Noggins adjust locally to back boxes so that they can be screwed in on 2 sides. Sole to sit on a length of that damp course that brickies use.

Does the membrane that's going under the flooring also run under the stud wall, up to and up the existing walls, with the the stud built on it? Or does the under flooring membrane just run up to the stud wall?
BC says sheet membrane runs under the sole and up to the wall..

Any thoughts on sheet membrane, does it need any geotextile type protective matting above/below?

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