My extension walls (2006 regs) are to be brick, full fill 75mm cavity batts, then aircrete inner leaf. I just thought, in theory, not that I'll do it, that if I wanted to use high density blocks inner leaf (will be fixing loads of cabinets etc to the wall), could I fit enough celotex in the walls to satisfy the (2006) regs. I mean, strong inner walls would be very nice ... just like the rest of the house ! Simon.
As long as your plugs and fixing screws go well into the blocks you need have no worries about strength ... assuming we're talking normal domestic loads. Or you can drill smaller holes and screw straight into the block, no plugs.
IIRC, 40mm Celotex was probably enough to give a U-value of 0.35W/m²K (I don't do a lot of domestic work these days, and it's amazing how quickly this info falls out of one's ears). Unless your extension is three or more storeys or is in an exposed location, a 25mm nominal residual cavity is OK.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.