Green Building Forum - No UFH in structural raft ! Thu, 25 Jun 2026 03:59:52 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219263#Comment_219263 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219263#Comment_219263 Thu, 12 Feb 2015 08:24:37 +0000 Triassic No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219265#Comment_219265 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219265#Comment_219265 Thu, 12 Feb 2015 08:38:34 +0000 orangemannot Pour a thicker insulated screed above the structural raft.
PS
i PLACED some insulation, 50mm polystyrene, below the raft as well.
then more above, below the screed, which was 100mm to 125mm
defence in depth if you like.]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219270#Comment_219270 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219270#Comment_219270 Thu, 12 Feb 2015 09:14:01 +0000 Triassic No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219284#Comment_219284 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219284#Comment_219284 Thu, 12 Feb 2015 10:37:09 +0000 dickster No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219286#Comment_219286 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219286#Comment_219286 Thu, 12 Feb 2015 10:41:13 +0000 joe90 No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219333#Comment_219333 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219333#Comment_219333 Thu, 12 Feb 2015 16:06:50 +0000 Greenfish
As for UFH in slab, how are you considering heating the water and what is your lifestyle? In slab will be very slow to respond. Great if you have GSHP and are there all day, permanently circling flow just above room temp.

Posted By: joe90How come Viking House does it with no problems???
Hope he will come along and say. Is it a suitable approach for all situations?]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219339#Comment_219339 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219339#Comment_219339 Thu, 12 Feb 2015 17:31:05 +0000 cjard
Hang on.. doesn't your architect work for you? If you don't like the answers and aren't being given an appealing justification, switch]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219342#Comment_219342 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219342#Comment_219342 Thu, 12 Feb 2015 17:48:20 +0000 Viking House Posted By: TriassicThe architect has said we can't place UFH pipes, zip tied to the reinforcing mesh, in the structural raft and that the UFH can only go in a screed layer above the completed raft. Did you ask him why not? We've done 100's without problems, there's about 50,000 done that way every year in Scandinavia.]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219345#Comment_219345 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219345#Comment_219345 Thu, 12 Feb 2015 18:15:34 +0000 CWatters The architect has said we can't place UFH pipes, zip tied to the reinforcing mesh, in the structural raft and that the UFH can only go in a screed layer above the completed raft. What are your thoughts, is he right?

I forget what stage you are at? Two options...

Screed with UFH
Insulation
Slab

Slab with UFH
Insulation
Ground

Normally screed is around 65mm thick and the slab 100mm thick. So the latter has more thermal mass/slower response time than the former.]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219349#Comment_219349 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219349#Comment_219349 Thu, 12 Feb 2015 18:32:01 +0000 Triassic Posted By: CWattersSlab with UFH > Insulation > GroundOur current home has the UFH pipes zip tied to the reinforcing mesh, so I'm happy with a slow response.]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219432#Comment_219432 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219432#Comment_219432 Fri, 13 Feb 2015 13:40:30 +0000 borpin Posted By: Triassicin the structural raftThe fact it is structural probably does it. Lots of pipes running through the concrete inevitably reduce the strength. Most houses have a concerete 'slab' rather than a full on raft. Just drop it by however much and screed it.]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219434#Comment_219434 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219434#Comment_219434 Fri, 13 Feb 2015 13:56:47 +0000 woodgnome The architect may be worried about different temps across the raft.]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219444#Comment_219444 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219444#Comment_219444 Fri, 13 Feb 2015 14:37:38 +0000 davidfreeborough
If he's concerned about the voids in the concrete then you can just make the concrete 20mm thicker to accommodate the pipe thickness. This should be at least as strong, after all, don't they often include voids in concrete to improve the strength to weight ratio?

If he's concerned about the increase in temperature of the slab causing differential expansion at floor/wall junctions then don't you get this problem in any case where the insulation is outside the structural component? You could argue that the problem is minimised by having both the load bearing slab and the walls on the warm side of the insulation layer.

If he's concerned by the temperature of the water then what temperature would be happy with? Does he realise that well insulated buildings can be heated with water just above room temperature?

David]]> No UFH in structural raft ! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219462#Comment_219462 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13099&Focus=219462#Comment_219462 Fri, 13 Feb 2015 16:21:53 +0000 ringi
At the very least the pipes will make the concrete connection to the steal weaker.]]>