Insulating a concrete slab

7 Feb 2024
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United Kingdom
Hi! I have permission to convert an old shop into residential and am getting some proper drawings made up for building regs. Trouble is, the consultant I am using has talked about 100mm jablite over the existing slab. My issue with this is that the street outside and the existing slab are more or less level, and to raise the level by over four inches might be feasible at the floor level but gives me all sorts of issues at the higher level (e.g. door frame height). Does anyone know whether this is an alternative that would provide sufficient U-values to satisfy Building Regulations? I was wondering whether 25mm Kingspan with a vapour layer and a thin screed prior to a finished floor would be favourable and be less of a ballache. Any advice will be gratefully received. Kind regards, Nigel
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25mm won't cut it, you might have to dig it out and do it the right way.

Or move the door frame and have a ramp.

Are you sure your existing slab isn't just screed on top of something else?
If you went with a PIR insulation such as Celotex or Kingspan then you would only need about half the thickness - 50mm. Alternatively you can get SAP calcs done whereby the insulation can be made thicker elsewhere to compensate, or perhaps your designer can produce the calcs. There's an excel spreadsheet on the web somewhere that's accepted by BC if I recall or used to be, though I think that was for extensions. Anyway the calcs don't cost too much from an assessor.
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Use a more efficient insulation product to achieve a thinner thickness.

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