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Hi folks i'm doing a self build extension my drawings ask for kingspan kooltherm k7 to be placed between the ceiling ties and the same above to achieve a maximum u value of 0.11w/m2k. The floor asks 175mm kingspan kooltherm K3 maximum u value 0.15w/m2k. Is there any insulation experts on here who could suggest an alternative cheaper product to kingspan to achieve the u values thank you.

Had this idea and wondering if anybody did this. To insulate the first floor from the top instead of struggling with overhead pushing rock wool between joists and then putting plasterboard on. The problem most of the times is that there is a ready installed subfloor (e. G. Tongue and groove chipwood boards) in place which is nailed/screwed and glued down long before any sound insulation is done inbetween floors. So it's not practical to go from the top. However The installation of insulation (maybe even loose, like cellulose) from the top, after the 1st fix electrics, plumbing.... Is done and plasterboard is installed to the ceilings, would be a lot less messy quicker and therefore maybe cheaper then fiddling rock wool or similar from the bottom. If you would put down large 2400x1200 plywood or osb sheets as a 1st floor subfloor without attaching them too much (just 3-6screws/board) in order to have a working platform while building. When all mvhr/electric/plumbing in the floor is done and it s sealed from the bottom with plasterboard, unscrew the boards, lift Row by row and stuff cellulose or loose eps (or whatever you fancy) down the void. Maybe even go a few mm higher then the Joists so by putting the osb/plywood back down you're compressing the insualtion a fair bit. Then attach the osb/plywood as usual with nails/screws and glue to the joists to finish the subfloor. A bit more work in laying the first floor boards, specially can see that as an issue if using the small chipwood t&g subfloor boards. But should be a lot quicker and easier to put insulation in. As always... Overcomplicating things. Or has anyone tried anything like this? Experience with it?

I introduced myself back in the ebuild days but I've mostly been lurking here since... thanks for all the interesting posts which I have enjoyed reading. For many years it was our intention to self build but failure to obtain planning permission (long shot) and failure to find another suitable plot meant we have settled for a renovation project instead. We dreamed of getting close to passive house standard on a new build. We have been living in our 1950s house in East Devon for a few months now and are trying to make decisions on what to do. Having read so many interesting response to people's queries I'm looking forward to asking a few questions. The highest priority for us is getting some heating, the old Aga that keeps only the kitchen warm has to go and we need something a bit more modern. We have filled the 50-80mm cavity with polystyrene (ThermaBead cavity Carbon Saver), which may have got the block/cavity/brick wall U value down to somewhere near 0.4. The loft has c. 200mm mineral wool. The Crittall windows will be changed at some point. I'm considering a GSHP. Given our EPC's heating requirement is quite large I think the RHI could be significant, especially as we have space for trenches so don't need the expense of a bore hole (we have spring water, I've got some questions to ask on that in another post). My question relates to floor insulation, or the absence of it. The ground floor is 67 sqm which is made up of 40 sqm of suspended floors (living room and dining room) and 27 sqm of concrete floors (kitchen, hall and cloak room). Taking up the suspended floor to insulate is relatively easy. Taking up the concrete floor would be a far less pleasant task. Having attempted to calculate the heating demand under a scenario where the whole floor is insulated verses one where only the suspended floor is insulated suggests it's not that big a difference. We're going to have plenty of cold bridges under the walls anyway. Would it be foolish not to take up the concrete floors and do the full job? Any tips on taking up a 1950s concrete floor?