Tom Posted August 5, 2021 Share Posted August 5, 2021 I've approached Wunda to give me a quote, but they are saying my proposed floor make up isn't possible. We plan to have an insulated slab, UFH pipes fixed directly to the top of the slab, then 75mm screed over the top of this. From what I've read this doesn't seem completely nuts, but they are saying they can't recommend fixing the pipes diectly to the slab. Is there any reason why we can't do what we plan? Link to comment Share on other sites More sharing options...
Temp Posted August 5, 2021 Share Posted August 5, 2021 The thermal mass would be very high (slow response time) but opinions differ on that. Link to comment Share on other sites More sharing options...
Mr Punter Posted August 5, 2021 Share Posted August 5, 2021 It will take too long to respond as lots of heat will go into the slab. A small amount of insulation on the slab would work. Link to comment Share on other sites More sharing options...
Tom Posted August 5, 2021 Author Share Posted August 5, 2021 I'm not bothered about response times tbh, I quite like the idea of having essentially a big storage heater! I'm sure I can't be the only one looking to put pipes directly on to a slab and screed over the top? Would the pipes fail due to differential movement or something? Link to comment Share on other sites More sharing options...
joth Posted August 5, 2021 Share Posted August 5, 2021 What do you mean by "fixed directly". Mechanically fixing it to the slab sounds hard work and likely to damage the pipes. Using their castellated panels would probably work well though? Link to comment Share on other sites More sharing options...
Tom Posted August 5, 2021 Author Share Posted August 5, 2021 Yep, clip rails or the castellated panels, either way UFH pipes on the slab then screed over the top. Link to comment Share on other sites More sharing options...
Nickfromwales Posted August 5, 2021 Share Posted August 5, 2021 16 minutes ago, Tom said: I'm not bothered about response times tbh, I quite like the idea of having essentially a big storage heater! I'm sure I can't be the only one looking to put pipes directly on to a slab and screed over the top? Would the pipes fail due to differential movement or something? Zero issues. I’m about to do the same in triple digits of M2 in screed and over existing ( insulated ) slabs. I absolutely will not be using the castellated trays, as I do not want the air gaps that are underneath. This faux pas is due to yet another architect who screamed “eco credentials” but failed to back that claim up. Otherwise the slabs would have been 75mm thicker and the UFH pipes encapsulated in the concrete. Can you not do this? Link to comment Share on other sites More sharing options...
Tom Posted August 5, 2021 Author Share Posted August 5, 2021 Thanks Nick. The issue is we need something to brace our ICF walls off while they're poured, and would need to bolt in to the slab for these, so having the UFH pipes in there would cause problems. Our slab is 200mm thick with two layers of mesh. It was initially spec'd as having the UFH pipes attached to the top layer of mesh, hence the issues with the ICF braces and thinking we could just take the pipes out and put in a screed over the top bwhen the walls are done. Tbh can see no reason why they can't be tied to the lower layer of mesh in the first place which would keep them out of the way of any bolts/screws. Link to comment Share on other sites More sharing options...
Tom Posted August 5, 2021 Author Share Posted August 5, 2021 ...though would we still need a screed for a final/level finish, even if we plan tiles/carpet/wood flooring in various areas? Link to comment Share on other sites More sharing options...
Russell griffiths Posted August 5, 2021 Share Posted August 5, 2021 @willbish did his pipes in the slab, he set up a system with scaffolding boards laid on the finished slab to take the screws for the props. He has probably got some pics if you if you ask him nicely. Link to comment Share on other sites More sharing options...
Tom Posted August 5, 2021 Author Share Posted August 5, 2021 Thanks Russell, will send him a PM. So, hypothetically speaking, if you were given a choice between: 200mm slab with two layers of mesh with UFH tied to LOWER mesh (i.e 150mm from surface) + 20mm for tiles or carpet etc OR 200mm slab, UFH on the top covered with 75mm screed + 20mm for tiles or carpet etc which would you go for? Both would have 300mm EPS below the slab. I'm thinking relative cost, floor heating responsiveness (big deal in a near passive house?), ability to "store" heat etc Link to comment Share on other sites More sharing options...
Triassic Posted August 5, 2021 Share Posted August 5, 2021 3 hours ago, Tom said: ...though would we still need a screed for a final/level finish, even if we plan tiles/carpet/wood flooring in various areas? We put our UFH pipes in the slab, attached to the mesh. We also used ICF braces. We simply left a slightly wider space between two rows of pipe and pegged out the centre line, using pegs hammered into the ground outside the slap.. we power floated the concrete a couple of hours after the pour, lovely smooth finish for carpets etc. and saves money. Link to comment Share on other sites More sharing options...
Triassic Posted August 5, 2021 Share Posted August 5, 2021 (edited) 5 minutes ago, Tom said: 200mm slab with two layers of mesh with UFH tied to LOWER mesh (i.e 150mm from surface) + 20mm for tiles or carpet etc No…. The UFH pipes are tied to the top mesh. I’d go for option 3 200 mm slab, UFH pipes tied to top mesh and power floated finish! Dont forget the insulation belowcthe slab. Edited August 5, 2021 by Triassic Link to comment Share on other sites More sharing options...
Tom Posted August 5, 2021 Author Share Posted August 5, 2021 Just now, Triassic said: No…. The UFH pipes tied tontura top mesh. I was just thinking that if tied to the bottom mesh we can bolt braces down anywhere without worrying. I can see this would affect responsiveness, but is that too much of a concern? For the main living area we are having the powerfloat as the final finish (albeit polished a bit and sealed etc), and one of the contractors said having the UFH pipes attached to the upper mesh would be a nightmare with moving the hose around, damage from boots etc etc. He recommended having it on the lower mesh. This slab would be going in after the ICF walls so no issues with bracing or anything though. Link to comment Share on other sites More sharing options...
Bitpipe Posted August 5, 2021 Share Posted August 5, 2021 3 hours ago, Tom said: ...though would we still need a screed for a final/level finish, even if we plan tiles/carpet/wood flooring in various areas? No, a few mm of self levelling compound will take care of that. Our basement floor was tamped flat - had a few high spots and snots that were chiselled off and the floor installer got it dead flat with compound. Link to comment Share on other sites More sharing options...
Bitpipe Posted August 5, 2021 Share Posted August 5, 2021 Two issues in play here a) how do you work around your need to bolt braces to the slab without damaging any UFH pipes b) position of UFH pipes in insulated slab in a passive house. Regarding b) you will have a very low heat injection requirement so the UFH will run at a low temp (35oC or thereabouts) when it is even needed. if you're using an ASHP you may want to run the slab cool in summer. Response time is not that relevant in a passive house as there is never a major call for heat - its a steady low level injection of heat and usually only in the coldest of months. Link to comment Share on other sites More sharing options...
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