We are just converting a barn which has solid 9inch brick walls. Our building reg drawings show 60mm celotex with 25x47mm battens with plasterboard.
Would it be better to spend more on this and improve the insulation on the walls? if so what is best to increase the 60mmm to lets say 70mm OR keep the 60mm and have insulated plasterboard?
any suggestions please. thanks

  • Mark Brinkley

    Your written detail isn’t altogether clear but 60mm of Celotex is probably a little on the minimal side for a modern structure, though undoubtedly enough to get through building regs. I’m not sure if there is an air gap involved here but generally once you get towards the higher end of the insulation spectrum, ensuring overall airtightness becomes just as important as adding extra insulation. In this respect, adding a different layer of insulation (e.g. insulated plasterboard) is likely to be more effective than just thickening one layer of insulation. Adding an air barrier might be more effective still, but care needs to be taken here around the issue of moisture migration – you don’t want water trapped inside the wall.

    In all probability, it’s best to take advice from the person who did the drawings. Say you are thinking of making the property more energy efficient and ask what he/she thinks is the best way of achieving this. Just adding 10mm on insulation may not make much difference and may have knock on effects elsewhere – e.g door openings.

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