Matt60 Posted March 22, 2021 Share Posted March 22, 2021 (edited) Will it work with a screed that thick? This question relates to the garage/workshop part of my new build only, the rest of the house will have the standard 75mm. The architect and structural engineer both know I wanted to have under floor heating in the garage and workshop because I spend a lot of time in there, particularly in the winter. However, in order to take the weight of a car, the screed needs to be 150mm thick and the SE has asked if my plumber (not selected yet) is willing to lay his system in this with the metal mesh that the SE has also specified. To quote the SE; "We would usually suggest a 150mm thick, RC35 slab in garages with A193 mesh in the middle." My immediate reaction to that question is; "Will the heat get through a slab that thick?" I don't need the garage to be house warm, on my old garage I used to heat it to 7 degrees to stop it hitting the due point and then just use a fan heater to top-up when working in there. I wonder if I might be better with a couple of big radiators with no trv's running as a slave on the ground floor UFH system. By that I mean say set the house to 22 degrees and the 2 garage rads would produce some heat as a by-product of the house reaching and maintaining 22 degrees, as the system effectively wouldn't know about the garage rads, which would mean the system is not trying to hit a target for the garage but should keep it above the due point. Then I could just top-up with a fan heater like I used to. Any guidance is appreciated, I need to go back to the structural engineer ASAP so he knows if the mesh is needed. He's specified the steel mesh just to stop the UFH cracking the screed but it won't be need if I go with rads or something else. Thanks. Edited March 22, 2021 by Matt60 Add Quote Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 22, 2021 Share Posted March 22, 2021 Drop the thickness to 100mm of c35 concrete on the mesh he suggests. Unless you are going to park a boeing 747 in there. This is standard spec for an insulated raft for the main house, obviously thicker at the edges to take wall loads, but thicker than 100 is not needed to park a car on. You are maintaining a drop in height from house to garage I presume. Just done mine, 100mm concrete with mesh, self levelling compound, interlocking plastic/ rubber floor tiles, no ufh. You need to forget screed and think concrete. Link to comment Share on other sites More sharing options...
Matt60 Posted March 22, 2021 Author Share Posted March 22, 2021 25 minutes ago, Russell griffiths said: Drop the thickness to 100mm of c35 concrete on the mesh he suggests. Unless you are going to park a boeing 747 in there. This is standard spec for an insulated raft for the main house, obviously thicker at the edges to take wall loads, but thicker than 100 is not needed to park a car on. You are maintaining a drop in height from house to garage I presume. Just done mine, 100mm concrete with mesh, self levelling compound, interlocking plastic/ rubber floor tiles, no ufh. You need to forget screed and think concrete. Thanks for the info, I'll feed that back and see what they say. Yes, the drop in height from the house to the garage has been accounted for thanks. Ignore the screed thing, that's me not him, he said R35 concrete, I just lose my way with all the different terminology. Where did you get your tiles from, are they any good, could you jack a car up on them without damage? Thanks again. Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 22, 2021 Share Posted March 22, 2021 (edited) Not fitted the tiles yet, but lots of American garages have them, I’m definitely looking at the tough polypropylene type not the foam ones. Edited March 22, 2021 by Russell griffiths Link to comment Share on other sites More sharing options...
Matt60 Posted March 24, 2021 Author Share Posted March 24, 2021 I spoke with the plumber that I will likely use for my self build and he had some reservations about this. He said that the heat up time will be hours (not really an issue) but that he was a bit concerned that the pipes will be contained in concrete which will have a stone content. He also wasn't sure if it might cause cracking. He didn't say he wouldn't do it but I think if he did it would almost certainly be at my risk and I could do without another thing to worry about. I think I might go with a couple of radiators instead, either not zoned (just take whatever passes through them while maintaining the main house target temp. Or zoned but set pretty low to stop the garage/workshop hitting the dew point and just top up with a fan heater. Does that sound like a reasonable solution or does anyone else have an alternative idea? Thanks. Link to comment Share on other sites More sharing options...
PeterW Posted March 24, 2021 Share Posted March 24, 2021 3 minutes ago, Matt60 said: he was a bit concerned that the pipes will be contained in concrete which will have a stone content. He also wasn't sure if it might cause cracking. He didn't say he wouldn't do it but I think if he did it would almost certainly be at my risk and I could do without another thing to worry about. Really ..?? May want to consider your choice of plumber as thermal cycling of concrete won’t crack it “just because it has stone in it”... There are very many people on here that will have issues if he’s correct ... Link to comment Share on other sites More sharing options...
joe90 Posted March 24, 2021 Share Posted March 24, 2021 Loads here have UFH pipes fitted to steel mesh within a concrete floor on insulation, yes heat up time is long but most tend to just keep it at a nominal temp 24/7 (I do mine). Link to comment Share on other sites More sharing options...
Matt60 Posted March 24, 2021 Author Share Posted March 24, 2021 Just now, PeterW said: Really ..?? May want to consider your choice of plumber as thermal cycling of concrete won’t crack it “just because it has stone in it”... There are very many people on here that will have issues if he’s correct ... Thanks, I think his concern was that the heat could make it crack and the stone would not be good against the pipes. I'm not sure to be honest. Have you known people lay under floor heating in this type of situation without issues? Link to comment Share on other sites More sharing options...
Matt60 Posted March 24, 2021 Author Share Posted March 24, 2021 (edited) 5 minutes ago, joe90 said: Loads here have UFH pipes fitted to steel mesh within a concrete floor on insulation, yes heat up time is long but most tend to just keep it at a nominal temp 24/7 (I do mine). Brilliant, thank you. I think it might be the case that I spooked him a little by saying my architect had asked me to ask the question. Your reply is appreciated and helpful as I will just go back and say I'm going for this as originally hoped. thanks again. Just further to this, I don't want to cost me a fortune to run. I'm happy to heat it just so it can't fall below 7 degrees and top up with a fan heater while I'm in there. Would you zone it or just run it as a slave part of the main system just taking whatever as a result of the main house say maintaining 22 degrees? Edited March 24, 2021 by Matt60 Add question 1 Link to comment Share on other sites More sharing options...
PeterW Posted March 24, 2021 Share Posted March 24, 2021 14 minutes ago, Matt60 said: Have you known people lay under floor heating in this type of situation without issues? Yes - every single member of this forum with a passive slab and UFH. He’s worrying about nothing. If he thinks UFH pipe is this delicate, ask him how many installs he has done as I think you may find it’s “not many” 1 Link to comment Share on other sites More sharing options...
PeterW Posted March 24, 2021 Share Posted March 24, 2021 Just on the garage you need to ensure it has its own controls and is isolated from the system in the house as otherwise you’ll need to insulate the walls and potentially the door too. 1 Link to comment Share on other sites More sharing options...
Matt60 Posted March 24, 2021 Author Share Posted March 24, 2021 16 minutes ago, PeterW said: Yes - every single member of this forum with a passive slab and UFH. He’s worrying about nothing. If he thinks UFH pipe is this delicate, ask him how many installs he has done as I think you may find it’s “not many” Thanks, Is a passive slab that sort of thickness then? I just assumed they would be the standard 75mm screed. Link to comment Share on other sites More sharing options...
joe90 Posted March 24, 2021 Share Posted March 24, 2021 8 minutes ago, Matt60 said: , Is a passive slab that sort of thickness the Yes! 1 Link to comment Share on other sites More sharing options...
Matt60 Posted March 24, 2021 Author Share Posted March 24, 2021 Thank you for the replies on here, that's really useful as I probably would have wimped out on this otherwise. ? 1 Link to comment Share on other sites More sharing options...
Matt60 Posted March 25, 2021 Author Share Posted March 25, 2021 12 hours ago, Matt60 said: Just further to this, I don't want to cost me a fortune to run. I'm happy to heat it just so it can't fall below 7 degrees and top up with a fan heater while I'm in there. Would you zone it or just run it as a slave part of the main system just taking whatever as a result of the main house say maintaining 22 degrees? 12 hours ago, PeterW said: Just on the garage you need to ensure it has its own controls and is isolated from the system in the house as otherwise you’ll need to insulate the walls and potentially the door too. Thanks. This is what I was getting at (above), what I mean is running the garage loop without a thermostat or trv's so the main house system doesn't "know" the garage loop exists. Therefore it would just take/get whatever heat is required to hit the house target and therefore not really place much extra cost to run? Does that make sense? Would that work? I don't need the garage to be house warm, just not to hit the dew point and therefore anything above 7 degrees is fine and easy to top up with a fan heater while working in there. Link to comment Share on other sites More sharing options...
PeterW Posted March 25, 2021 Share Posted March 25, 2021 Ok so for the sake of an actuator (£15) and a cheap thermostat (£10) you get control that means you don’t overshoot the temperature or dump large quantities of heat into a building that you want at a lower target temperature. 1 Link to comment Share on other sites More sharing options...
Matt60 Posted March 25, 2021 Author Share Posted March 25, 2021 1 minute ago, PeterW said: Ok so for the sake of an actuator (£15) and a cheap thermostat (£10) you get control that means you don’t overshoot the temperature or dump large quantities of heat into a building that you want at a lower target temperature. Right, I see thanks, that makes sense, I'll do that. So does that mean it would be a separate zone? Sorry, still learning... Link to comment Share on other sites More sharing options...
PeterW Posted March 25, 2021 Share Posted March 25, 2021 Yep it would be a separate zone. 1 Link to comment Share on other sites More sharing options...
coconutsaregood Posted April 3, 2021 Share Posted April 3, 2021 The garage is good example where humidity control is more important than air temperature. Has anyone used a humidistat instead of thermostat for controlling the heating? I know to keep humidity to the idea of 55 to 65 % RH you have to maintain a differential of plus 7 degrees over outside temperature in the winter season. Link to comment Share on other sites More sharing options...
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