psirus

It wouldn't be sitting on top of an insulated slab. Its a 1970s house with zero floor insulation. I think after all of the comments and I am going to scale back this project and only fit UFH in 2 of the smaller rooms which are currently being renovated. Rather than just remove the screed I will take out the whole slab and start the floor from scratch. The manifold will be in an empty room so I don't mind leaving the floor and pipes exposed here so that I can add UFH to the other rooms at a later date. I am thinking 10mm type 1, 150mm PIR and 50mm liquid screed over the UFH pipes. Should I add more insulation to the floor or is 150mm enough? The big radiators in the living/dinning room area only have 8mm pipes going to them for reasons only the previous owners and explain. I will fit 15mm pipes to them and that should help things this winter. Hopefully next year I will be in a position to extend the UFH into this space.

So assuming I add 100mm of insulated plasterboard as you suggested, would my UFH spec be good enough? I would most likely be happy to add the PIR to the roof but this would come at a later date. Right now the decision to remove the screed and install UFH is blocking progress so need to make a decision if I should do it or not.

If reducing the screed (and thermal mass) and adding a little extra insulation would give a better end result then I would be interested is those liquid screed solutions, thanks for highlighting them.

I am not really expecting the UFH to overcome the heat loss from the roof all I really want is the bottom half of the room to be a comfortable temperature. Would my plan achieve that? I am still keeping the radiators for days when it's really cold. My basic thinking is that for the heat to be lost out of the roof then it would first have to pass the comfort zone I am after. Granted the system would not be able to turn off if the heat lost is too great from the roof. Just trying to decide if it's worth doing from a comfort perspective. Would 30mm of insulation allow the 46mm of screeds thermal mass to create a comfortable temperature in the bottom half of the room? Or would I lose too much heat into the floor? There are lot of retro fit systems out there that just sit on top of the floor and don't even have any screed for thermal mass which made me think my plan would at least get some ways towards the benefits of a real UFH install. If its just a case of it will cost more to run because of the 30mm floor insulation but still get the same comfort benefit as if I had 100mm floor insulation then I think I would probably just go for it. If its a case of the heat output will be terrible and mostly lost into the floor and I wont be really any warmer then I might wait a few years and just dig up the floor entirely. Thanks for taking the time to read my posts and guide me to the right decision.

50mm is a lot more than what was there let me tell you! But I take your point that really could do with more however we really didn't want to lose any of the exposed beams. Even with 150mm of PIR in the ceiling I cannot see it making much different since the massive void with still take all the heat away from where it's needed at ground level when using radiators. My thinking was that URH would keep the bottom half of the room warm the and top much cooler. The Tarmac liquid screed that the screed guy quoted for is suitable to be used with only 40mm depth but it has to be at least 30mm above the pipes as well. So technically I would have 46mm of screen as a thermal store. Yes you are correct I forgot to mention the 30mm celotex I wanted to put under the pipes. I cannot seem to edit the original post to fix that.

Hi All I am considering retro fitting UFH in my 1970s house. I am really wanting to do this because the radiators just don't do enough in the open plan dining/living room area. Cavity wall insulation was added about 20 years ago by the previous owners and I have since added as much PIR to the pitched roof areas as I could fit. Adding more radiators wont help much as all the heat will just go straight up away from where is needed. The dining room ceiling starts at 3m heigh and finishes 5m, any heat from the radiator in the living room just spills out into the high dining room ceiling. The pitched dining room ceiling has 50mm celeotex between the rafters. My current plan would be to remove the screed which is roughly 6cm thick, lay 16mm pipes, liquid screed up to 30mm above the pipes. That would mean only a 16mm increase in height across the downstairs floor which is ideal because only the dining room has a high ceiling the other rooms are all standard height. Please see attached photos to get an idea of the open plan space and the screed depth from a small test hole. The rest of the downstairs is heated just fine by radiators but since the floor heigh will increase I would want to add UFH everywhere. So my questions are should I do this? Will it make a worthwhile difference or would I lose to much heat into the floor? Should I put this project on hold and maybe one day dig out the entire floor and add extra insulation? I cannot see this open ever happening as it would cost a whole lot more that just removing the screed but maybe I can be convinced. Any other comments, concerns or advice would also be welcome. Many thanks