Obi_wan Posted March 3 Share Posted March 3 Planning to construct our extensions suspended timber floor next week and looking for feedback on getting a good airtight and insulated ground floor. I would like to install underfloor heating in this room but could give it up. the most common proposal seems to weave the an airtight membrane up and over each joist, insulate between joists and vapour control over the top. Is this aimed at retrofitting and not newly constructed floors? Could the bottom airtight membrane not be laid below the joists? Alternatively I have thought about 150mm PIR between the joists. Finished with PIR going over the top of the joists to deal with cold bridges. This top PIR could be used to clip the underfloor heating pipes. any advice would be appreciated Link to comment Share on other sites More sharing options...
ProDave Posted March 3 Share Posted March 3 I used 300mm I joists. 300mm Frametherm 35 between the joists. Then air tight membrane taped and sealed to the building walls. 12mm OSB. Battens following line of joists. UFH pipes between battens, dry pug mix for heat dispersal, then finished floor (engineered Oak) Design joists for the extra dead load of the pug mix and allow for the height build up. Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 3 Share Posted March 3 Why the timber floor ? you could use block n beam or concrete slab. you are making a lot of work for yourself for no apparent benefit . Link to comment Share on other sites More sharing options...
Obi_wan Posted March 3 Author Share Posted March 3 Sloped plot with 1.2m going to 2.0m drop. Too late now but do have a beam and block patio. From organising that I have discovered the following. Beam and block has proven to be very expensive in Scotland. Robslee are making to order with 4 week lead. Much better prices down south, but few suppliers willing to ship. The ones who have quoted have big transport fees. Moving beams are going to be challenging. Link to comment Share on other sites More sharing options...
Obi_wan Posted March 3 Author Share Posted March 3 56 minutes ago, ProDave said: I used 300mm I joists. 300mm Frametherm 35 between the joists. Then air tight membrane taped and sealed to the building walls. 12mm OSB. Battens following line of joists. UFH pipes between battens, dry pug mix for heat dispersal, then finished floor (engineered Oak) Design joists for the extra dead load of the pug mix and allow for the height build up. this is interesting. Was the frametherm just friction fit or did you uses something to hold it? what depth of dry plug mix? Thanks Link to comment Share on other sites More sharing options...
saveasteading Posted March 3 Share Posted March 3 33 minutes ago, Obi_wan said: but few suppliers willing to ship. Have you explained to them that Scotland has some roads these days? I'm not being facetious. The ignorance of some southerners (I live among them) about anything north of London is remarkable. As you will know, Perthshire, transport included, Inverness-shire (and some of Aberdeenshire) not. Either 'impossible', or add a lot for delivery. A good builders' merchant can possibly sort this for you. usually I'd favour a local one, but the nationals may have deliveries coming in from all over. 45 minutes ago, Obi_wan said: . Moving beams are going to be challenging. No more than other methods in my opinion. I've often used them on sloping sites. Link to comment Share on other sites More sharing options...
Obi_wan Posted March 3 Author Share Posted March 3 6 minutes ago, saveasteading said: Have you explained to them that Scotland has some roads these days? I'm not being facetious. The ignorance of some southerners (I live among them) about anything north of London is remarkable. As you will know, Perthshire, transport included, Inverness-shire (and some of Aberdeenshire) not. Either 'impossible', or add a lot for delivery. A good builders' merchant can possibly sort this for you. usually I'd favour a local one, but the nationals may have deliveries coming in from all over. No more than other methods in my opinion. I've often used them on sloping sites. I tried 4 different BM nearby in Glasgow area, 2 local and 2 national, that I have been using for other materials. They were all going to the same place, Robslee. Prices varied very little. All were double the price per beam of those I found down south. Link to comment Share on other sites More sharing options...
Obi_wan Posted March 3 Author Share Posted March 3 (edited) 4 hours ago, ProDave said: I used 300mm I joists. 300mm Frametherm 35 between the joists. Then air tight membrane taped and sealed to the building walls. 12mm OSB. Battens following line of joists. UFH pipes between battens, dry pug mix for heat dispersal, then finished floor (engineered Oak) Design joists for the extra dead load of the pug mix and allow for the height build up. I have read that you created a ledge under the I joists to hold the insulation. The plug mix covered the depth of the battens. What is the purpose of the 12mm OSB? Is it to stop the insulation being compressed by the dry mix? I am wondering if I could omit this if I used PIR instead. I have the joists so I can adjust the centres but not the depth. At 200mm frametherm wouldn’t meet the U valve. Edited March 3 by Obi_wan Link to comment Share on other sites More sharing options...
ProDave Posted March 3 Share Posted March 3 1 minute ago, Obi_wan said: What is the purpose of the 12mm OSB? Is it to stop the insulation being compressed by the dry mix? I am wondering if I could omit this if I used PIR instead. I have the joists so I can adjust the centres but not the depth. So 200mm of frametherm wouldn’t meet the U valve. Yes to support the pug mix and to fix the UFH pipes to. 1 Link to comment Share on other sites More sharing options...
Super_Paulie Posted March 3 Share Posted March 3 I'd go with the 150mm PIR, best bang for your buck and if it's supported on battens then it's rock solid ready for your pug mix. Here's my 170mm version, just need to tape over the joins. 1 Link to comment Share on other sites More sharing options...
Obi_wan Posted March 4 Author Share Posted March 4 12 hours ago, ProDave said: Yes to support the pug mix and to fix the UFH pipes to. The finished floor is undecided and could be tiles, LVT or wooden floor. Am I right in saying that this build up would only allow for engineered wooden flooring because this is being substituted in for the structural floor. Does that mean 18 or 22mm moisture board, like caberdek, or OSB could be used instead of the 12mm OSB and I would have more flexibility in the finished floor selection? Link to comment Share on other sites More sharing options...
Obi_wan Posted March 4 Author Share Posted March 4 12 hours ago, Super_Paulie said: I'd go with the 150mm PIR, best bang for your buck and if it's supported on battens then it's rock solid ready for your pug mix. Here's my 170mm version, just need to tape over the joins. What’s your finished floor buildup plan? Link to comment Share on other sites More sharing options...
Super_Paulie Posted March 4 Share Posted March 4 ive got 22mm caberdeck and then LVT. I got the caberdeck before i was reallly educated on the subject and i needed a structural floor to live on for the last year and a half while the build was ongoing. If i could go back id get something that isnt an insulator like cement board or whatever but it is what it is, ive already got it. If its rubbish i'll just switch the floor out in the future but quite frankly the house is warm enough as it is with having the radiators on for 10 minutes as its so well insulated and air tight. I put rads in as a backup incase the UFH doesnt work as intended (and to dry clothes etc!), the room is 90sqm open plan. In fact, if i could go back i wouldnt even bother with the UFH, but im all in now. Link to comment Share on other sites More sharing options...
Obi_wan Posted March 4 Author Share Posted March 4 16 minutes ago, Super_Paulie said: ive got 22mm caberdeck and then LVT. I got the caberdeck before i was reallly educated on the subject and i needed a structural floor to live on for the last year and a half while the build was ongoing. If i could go back id get something that isnt an insulator like cement board or whatever but it is what it is, ive already got it. If its rubbish i'll just switch the floor out in the future but quite frankly the house is warm enough as it is with having the radiators on for 10 minutes as its so well insulated and air tight. I put rads in as a backup incase the UFH doesnt work as intended (and to dry clothes etc!), the room is 90sqm open plan. In fact, if i could go back i wouldnt even bother with the UFH, but im all in now. Ok thanks. I haven’t bought the caberdek yet, but thinking I could place it on top of the joists and before the pug mix. It should contribute to the thermal resistance below the ufh and provide the structural flooring. Alternatively I could look at cement board and put it on top of the pug mix and it will contribute to the heat dispersion. Not sure what thickness of cement board would be required for a solid floor feel, spanning between the 400mm centred battens. Link to comment Share on other sites More sharing options...
saveasteading Posted March 4 Share Posted March 4 16 hours ago, Obi_wan said: All were double the price per beam of those I found down south. I had a quick look online. Nationwide BM say it's the same delivery cost anwhere except the Highlands ( it must be the ferry crossings to those mountainous islands). Maybe it's just got more expensive. Link to comment Share on other sites More sharing options...
saveasteading Posted March 4 Share Posted March 4 1 minute ago, Obi_wan said: cement board would be required for a solid floor feel, spanning between the 400mm centred battens. This feels all wrong. Why not simply a latex screed? It isn't spanning it is just sitting there. In fact a cement board might be the least good option as it is brittle. Hoping that your joists are tanalised and the void is well ventilated. Link to comment Share on other sites More sharing options...
Obi_wan Posted March 4 Author Share Posted March 4 11 minutes ago, saveasteading said: This feels all wrong. Why not simply a latex screed? It isn't spanning it is just sitting there. In fact a cement board might be the least good option as it is brittle. Hoping that your joists are tanalised and the void is well ventilated. the cement board like no more ply would be on top of the pug mix or latex screed as you have suggested. It would then accept tiles and provide a structural floor. Link to comment Share on other sites More sharing options...
saveasteading Posted March 4 Share Posted March 4 47 minutes ago, Obi_wan said: on top of the pug mix The chances of it sitting snugly are low, and if it spans any distance it will sound hollow/ perhaps snap under load. Ply would be better, but I think latex given where you have got to. I like innovation but sometimes it becomes an experiment, with risk. Up to you really. Link to comment Share on other sites More sharing options...
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