JayDee

Is it common practice to put dpm (joins taped) beneath and above the pir or just beneath?

Thanks dude, your advice and others on this forum is immeasurable!

Yes the A193 mesh will definetly be supported on 70 or 90mm height chairs anyway. So the the mesh is about 50mm below the surface no matter what. Mesh should usually always be on chairs to reinforce it correctly, especially at this thickness. I've just heard different things about placing the pipes. Some say install pipes directly on the pir at the very bottom of the screed (beneath the mesh that's on support chairs). Others have said put the pipes on top of the mesh so it is halfway or 50mm from the surface. Wunda advised not to do this and to put the pipes directly on the pir at the bottom of screed, even if it were 125 to 150mm of screed. It's interesting though because this exercise, I've come across this a few times. ufh installers, some say put it in the middle of the screed tied on the mesh so they're suspended in the upper half of the screed. Some say not to and put the pipes at the bottom of screed directly on the insulation.

Another conflict I've come across in ufh industry advice with this job (not just on this forum). Is some say tie the pipes to the mesh halfway to 50mm from the surface of the screed. Others say don't, and install the pipes directly over the pir at the bottom of the screed. Even Wunda recommended to install on the pir and not on the mesh. What's the general consensus on that one?

All very helpful information. There is an internal wall going in, splitting the extension equally into two rooms/zones with a door way on the left hand side (the existing building side). Internal wall extending from the centre column to the outside wall. (see picture) I was considering cutting a joint 1/3 depth of slab, beneath the internal wall however was wondering I might getaway without it as the joint will then be exposed in the door way. Not heard of the inducers before, is this a better way of doing it and what type of inducer and where to get? The last conundrum I'm battling is, do I need to add another 25mm pir boards on top of the 100mm or will the 100mm pir be ok? One ufh guy i spoke to said don't worry, another ufh guy said add it, but mainly to decrease the slab thickness. After reading the comments above, I'm ok with the slab thickness heating slower if there's no significant increase in energy consumption. Though I will add 25mm pir if 100mm pir isn't enough. If it's not a big deal, so long as the joins are taped properly I'll save the faff adding the additional pir... thoughts?

Yes that's right. exposed agg polish then sealed. small surface cracks are always expected. It's the slab cracking all the way through the thickness that I'm trying to avoid. This can be controlled with cut contraction joints, 150mm screed thickness , miothene foam around the block dpc and A193 mesh will be going in to reinforce. Due to the size of slab I'm just on the limit to avoid cutting a contraction joint. So wanted to do everything else to limit any big cracking to occur.

Cheers. Yes its an air source hp . So the idea would be to run at low temp continuously through cool months. the slow response time is not too much an issue. My main concern is at 150mm is it still going to work, or will it use too much energy and not work very well? So long as it does work and not take too much energy from the hp system to maintain, or be very inefficient. If its worth going for then I'm keen to have ufh installed. Or happy to take other recommendations for alternative heating should this be a no go. I know rads aren't great for hp systems. What about wall heating systems like variotherm? Or the skirt heating systems? Looking for the best advice under the circumstances really. Should I go for the ufh? Or is there a better solution based on this particular set up? I can throw in another 25mm pir boards ontop of the 100mm I already have. If this will make a huge beneficial difference. However not ideal due to the polished concrete/exposed agg finish. Answers from all commentors welcome. Thanks again.

Looking for some advice please. Doing a 8.5m x 4.4m concrete slab for a house extension. Substrate to slab floor height is a total of 250mm. Dpm and 100mm insulation going in first, then pour a 150mm concrete slab over the 100mm insulation. Reason for the 150mm thick concrete is for polished concrete floor finish, to help prevent the slab cracking. I'm aware the overall max recommendation for screed on ufh pipes is 100mm . Although with 150mm screed thickness over the ufh pipes that are at the bottom of screed, and on top of the insulation. Will it still work ok? Or should this be avoided? I guess it would take longer to heat up, but if its set and maintained temp it should still store the heat and work ok? I could possibly add 25mm insulation to increase to 125mm and decrease concrete thickness to 125mm if needed. Although not ideal, as can increase the risk of slab cracking. ufh would be best as the existing house already has a heat pump ufh system, and adding two zones in the new extension is fine for the current system to cope. However, due to the 150mm thick concrete screed, should another heating method be considered instead? Like radiators etc... instead of ufh? Picture attached. Thanks in advance.