Adsibob Posted March 2, 2021 Share Posted March 2, 2021 Our floor build up on our ground floor was meant to be as follows: FFL: Porcelain tiles, underlay and adhessive (15mm) Screed containing 16-18mm wet UFH pipes (55mm) Tacker insulation panel (100mm) DPM Sand binding (10mm) Concrete Slab Hardcore For reasons I won't go into, a structural concrete encased beam has ended up in the floor about 150mm higher than was intended. This means that there is no space to lay underfloor heating over that area unless we raise the floor. The area is a narrow but very long rectangle, spanning 7m in length (basically the whole width of the house) by about 25cm in width. We cannot raise the floor by more than about 55mm. If we do this, Architect thinks we would have space to lay (just over this narrow 7m strip) about 30mm of insulation and 25mm of screed. We would keep to the above build up for everywhere else in the floor and also add some polystyrene to the sides of the concrete encased beam to minimise cold from that. Overall this accounts for maybe 4% of the overall floor space, so whilst it's incredibly annoying I'm trying to remain calm and find a solution. I need to look into the exact type of insulation, but it would be something high end that could. Not sure if Aerogel would work. Also not sure if this is as strong as tacker insulation or if the compressive strength of the insulation is irrelevant. Does anyone see a problem with the above solution, apart from the fact that the floor over that strip will have a bit more heat-loss? Is there an issue with screed being 55mm deep in most of the floor and only 25mm deep over that portion (i.e. on the narrow strip the underfloor heating pipes would be 30mm higher and closer to the FFL than the rest of the floor, which would mean they would have to transport the water against gravity for that small jump). If that's a bad idea, would it make sense to lose screed on the rest of the floor or is that also a bad idea? Should I just have a cold patch with no underfloor heating on this bit of the floor? It's in the middle of an open plan and otherwise well insulated space in a 1930s conversion and extension. Link to comment Share on other sites More sharing options...
Faz Posted March 2, 2021 Share Posted March 2, 2021 Rearranging the loops to avoid the 250 mm gap will be fine - it won't result in a cold spot as the concrete slab will conduct the heat across it. Kingspan Optim R is the best floor insulation with the least thickness but I am not sure you can get it in really small widths (and you can't cut it as it is vacuum sealed). Link to comment Share on other sites More sharing options...
Adsibob Posted March 2, 2021 Author Share Posted March 2, 2021 (edited) 6 minutes ago, Faz said: Rearranging the loops to avoid the 250 mm gap will be fine - it won't result in a cold spot as the concrete slab will conduct the heat across it. Kingspan Optim R is the best floor insulation with the least thickness but I am not sure you can get it in really small widths (and you can't cut it as it is vacuum sealed). Thanks @Faz . So coincidentally, the two heating zones for that floor almost fall exactly either side of the beam that is too high up. So maybe we just give up on having heating on that strip. I still think there will be some cold patches there though. Edited March 2, 2021 by Adsibob Link to comment Share on other sites More sharing options...
Faz Posted March 2, 2021 Share Posted March 2, 2021 This is the ufh loop going into my house late last year - like I say - 250mm isn't worth worrying about mate. Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 2, 2021 Share Posted March 2, 2021 What’s the sand blinding for, that’s not needed. Link to comment Share on other sites More sharing options...
Adsibob Posted March 2, 2021 Author Share Posted March 2, 2021 13 minutes ago, Russell griffiths said: What’s the sand blinding for, that’s not needed. My understanding is that it is to level the roughness of the concrete slab but 10mm might be overkill. Would 5mm be ample? Link to comment Share on other sites More sharing options...
Faz Posted March 2, 2021 Share Posted March 2, 2021 If the firm you are using to screed is any good you won't need any - this is my finished screed - nothing required on top of that. Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 2, 2021 Share Posted March 2, 2021 2 hours ago, Adsibob said: My understanding is that it is to level the roughness of the concrete slab but 10mm might be overkill. Would 5mm be ample? No nothing, it’s meant to go on top of hardcore to take out the sharp pointy bits, not needed on a concrete slab. Link to comment Share on other sites More sharing options...
Adsibob Posted March 2, 2021 Author Share Posted March 2, 2021 2 minutes ago, Russell griffiths said: No nothing, it’s meant to go on top of hardcore to take out the sharp pointy bits, not needed on a concrete slab. I think you are right and my architect has listed them in the wrong order. It should go below the concrete slab on top of the hard core. Link to comment Share on other sites More sharing options...
Russell griffiths Posted March 2, 2021 Share Posted March 2, 2021 I don’t think you have allowed enough for your tiles, I’ve allowed 25mm overall for a 10mm tile. That’s with matting. Link to comment Share on other sites More sharing options...
Adsibob Posted March 2, 2021 Author Share Posted March 2, 2021 19 minutes ago, Russell griffiths said: I don’t think you have allowed enough for your tiles, I’ve allowed 25mm overall for a 10mm tile. That’s with matting. Thanks @Russell griffiths . The tiles I'm laying are only 6mm thick. I will query with the architect why he hasn't allowed 21mm overall. Link to comment Share on other sites More sharing options...
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