richo106 Posted July 23, 2021 Share Posted July 23, 2021 We have just bought a 1960's bungalow with a suspended floor, the gap underneath ranges from 700-400mm. The joists are currently 50 x 100mm My plan for the renovation was the installed UFH throughout on the ground, between the joists I would lay 75mm kingspan insulation, then clipping UFH pipes then screed 25mm up to the level on the joists. Then floorboard/tile board for tiles to be laid on. I was just wondering if the joists would be strong enough to hold this extra weight? They are supported underneath at intervals by brick walls (with air gaps) but not sure exactly how far apart yet until I do further investigation What are peoples initial thoughts? How would they go about this? Many Thanks Link to comment Share on other sites More sharing options...
Temp Posted July 23, 2021 Share Posted July 23, 2021 I suspect they might carry the weight but might not be rigid enough to stop tiles cracking. One test I've seen mentioned is to put a glass of water on the floor and have someone walk around. If you can see the surface if the water vibrating then it's not rigid enough. Not very scientific though. Link to comment Share on other sites More sharing options...
tonyshouse Posted July 23, 2021 Share Posted July 23, 2021 Why do you want screed? It will work without it Link to comment Share on other sites More sharing options...
richo106 Posted July 23, 2021 Author Share Posted July 23, 2021 25 minutes ago, Temp said: I suspect they might carry the weight but might not be rigid enough to stop tiles cracking. One test I've seen mentioned is to put a glass of water on the floor and have someone walk around. If you can see the surface if the water vibrating then it's not rigid enough. Not very scientific though. Have you any methods to help it be rigid enough as you can imagine I don't want the tiles cracking!? Link to comment Share on other sites More sharing options...
richo106 Posted July 23, 2021 Author Share Posted July 23, 2021 26 minutes ago, tonyshouse said: Why do you want screed? It will work without it Thats just a method I have seen online when doing my research, have you any other methods that would work? Thanks Link to comment Share on other sites More sharing options...
Temp Posted July 23, 2021 Share Posted July 23, 2021 24 minutes ago, richo106 said: Have you any methods to help it be rigid enough as you can imagine I don't want the tiles cracking!? If the joists deflect/bend too much then normally I'd suggest replacing with solid floor (hardcore, sand blind, DPM, insulation, UFH in screed) but if you have 700mm deep voids it might be worth replacing the 100mm joists with deeper or possibly a beam and block floor (B&B, DPC, insulation, UFH in screed). Alternatively add more supporting walls under the 100mm joists. If sticking with 100mm joists I would fit 100mm insulation between them. Then board with something like two layers of 18mm WBP screwed down at 150mm centres then use an UFH system like this one on top.. https://ambienteufh.co.uk/tiling-over-underfloor-heating/ I might be wrong but think this type is limited to medium and large format tiles. Not small mosaic as they can be damaged by point loads. The more insulation below the UFH the better. Less wood above is also better. Link to comment Share on other sites More sharing options...
tonyshouse Posted July 23, 2021 Share Posted July 23, 2021 Insulate underneath 2 to300mm and pipes above with a sealed air void or spreader plates. Where can the heat go? It has to warm the floor turning it into a radiant floor. my floor sometimes has ufh, rarely but flow temp is never above 20 and with people, lighting etc the room is slightly warmer Link to comment Share on other sites More sharing options...
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