ectoplasmosis Posted December 13, 2023 Share Posted December 13, 2023 We're about to start building a single-storey rear extension to a Victorian semi, with a flank cavity wall which butts up to a neighbour's existing wall. Would it be possible to use 75mm-wide medium-density concrete block for the inner skin of the cavity wall, instead of the normal 100mm? This would allow us to increase the cavity size and use full-fill Dritherm 32 insulation instead of PIR, eliminating the risks with using rigid board inside a cavity. Link to comment Share on other sites More sharing options...
Mike Posted December 13, 2023 Share Posted December 13, 2023 (edited) Building Regulations Approved Document A requires a minimum thickness of 90mm, so to go thinner than that you'd need Structural Engineer's calculations to prove that it's adequate. Edited December 13, 2023 by Mike Link to comment Share on other sites More sharing options...
Russell griffiths Posted December 13, 2023 Share Posted December 13, 2023 As above, they are for internal walls. If your tight on space look at a different build bethod, sips panels and a block outer skin, or timberframe and brick/block outer, cavity construction takes up a lot of room for very little insulation value. Link to comment Share on other sites More sharing options...
Conor Posted December 13, 2023 Share Posted December 13, 2023 Good case for timber frame with block outer skin. 1 Link to comment Share on other sites More sharing options...
joe90 Posted December 13, 2023 Share Posted December 13, 2023 3 minutes ago, Conor said: Good case for timber frame with block outer skin. Yes then insulation within the timber frame as well 👍 Link to comment Share on other sites More sharing options...
Jane W Posted October 20 Share Posted October 20 On 13/12/2023 at 00:06, ectoplasmosis said: use full-fill Dritherm 32 insulation instead of PIR, eliminating the risks with using rigid board inside a cavity We are planning a newbuild atm but have the same quandary. Can insulated plasterboard or insulating render bring the u value up to building regs if you go 100mm medium density blocks and dritherm? Link to comment Share on other sites More sharing options...
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