Green Building Forum - Fitting UFH on/in concrete

Green Building Forum - Fitting UFH on/in concrete Thu, 30 Apr 2026 11:00:18 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95233#Comment_95233 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95233#Comment_95233 Fri, 26 Nov 2010 01:11:29 +0000 wookey
1) how do you attach the pipe to the existing concrete in order to pour the screed? There are various plastic formers you can get to wrap pipe round but they assume you have insulation underneath. Using them above concrete would just separate most of your useful thermal mass. Similarly there are various fixings to attach pipe to insulation - but I haven't seen any to attach pipe to concrete.

2) why separate the concrete and the screed? Why not pour it all in one? Is it just some practical reason to do with what's easy in building (concrete can be all wonky - screed will sort it out?) We'll be putting tiles on top so it only has to be 'quite flat'. And I've seen people polishing their concrete in order to use that directly as the floor surface. Is that expensive (this is a relatively small 28m2 area)? We can dig out less deep and save a skip or three of soil-shifting if we just skipped the screed and did it all in one, making efforts to ensure it was flat enough. Is there a good reason not to? In this case the UFH is normally tied to the rebar grid that goes in the floor slab, which seems simple enough]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95240#Comment_95240 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95240#Comment_95240 Fri, 26 Nov 2010 08:46:15 +0000 CWatters
There are also systems that claim to allow tiling direct onto the insulation but I've not used them.

Thermal mass has positives and negatives. Takes a long time to heat up a large floor mass of concrete. The importance of that depends if your house is unoccupied a lot eg are you both at work 9-5?]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95242#Comment_95242 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95242#Comment_95242 Fri, 26 Nov 2010 09:42:26 +0000 ted
Concrete slab and screed are different beasts, screed for UFH usually containing fine fibre to provide reinforcement to prevent micro-cracks. Not sure if they also have slightly different thermal properties.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95252#Comment_95252 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95252#Comment_95252 Fri, 26 Nov 2010 11:27:16 +0000 davidfreeborough Posted By: wookey1) how do you attach the pipe to the existing concrete in order to pour the screed? If you're using a sand & cement screed then there's no need to fix the pipes to the concrete. Instead tie wrap the pipes to steel reinforcement mesh.

Posted By: wookey2) why separate the concrete and the screed? Why not pour it all in one?

It's mainly for practical reasons. The underfloor heating pipes need to be filled, connected to a manifold & pressurised while the concrete is being poured & finished. That is easier said than done when the site is a sea of mud, there are no walls to mount the manifold on & there are no existing services. For your extension this may be less of an issue.

The other issue as CWatters has mentioned is that you may end up with a very long response time. In some situations it may be unacceptable, but in a Passivhaus with an Economy 7 heat pump this can be a plus point.

Power floating (polishing) the slab doesn't cost much, just the hire of the machines & a few extra hours labour. However, you need to take care to protect the slab during the later stages of construction.

David]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95256#Comment_95256 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95256#Comment_95256 Fri, 26 Nov 2010 12:19:31 +0000 MarkBennett Posted By: davidfreeboroughThe other issue as CWatters has mentioned is that you may end up with a very long response time. In some situations it may be unacceptable, but in a Passivhaus with an Economy 7 heat pump this can be a plus point.

First, I very much favour the idea of insulation under the slab, especially if joined up to external wall insulation, to minimise thermal bridging.

However, I think that integrating the UFH pipes into the full slab will result in too much thermal mass and a very slow response time. You would basically need to have your heating on 24/7, at a very low level. I suspect that getting the temperature stable in a low energy dwelling, especially one with large passive solar gain, and therefore subject the weather variations (even on a short timescale) would be tricky.

I think that separating the structural slab from the screed using a thin layer of insulation is probably the best compromise. This uses the thermal mass of the screed, but is not slowed too much by the thermal mass of the structural slab.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95261#Comment_95261 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95261#Comment_95261 Fri, 26 Nov 2010 13:13:03 +0000 davidfreeborough Posted By: MarkBennettHowever, I think that integrating the UFH pipes into the full slab will result in too much thermal mass and a very slow response time. You would basically need to have your heating on 24/7, at a very low level.In a Passivhaus heated by an Economy 7 heat pump you need thermal mass to store heat for the 21 hours the heating isn't on. Additional thermal mass leads to less variation in temperature & a lower risk of overshoot. Lower thermal mass will increase the risk of overheating due to incidental gains.

Posted By: MarkBennettI suspect that getting the temperature stable in a low energy dwelling, especially one with large passive solar gain, and therefore subject the weather variations (even on a short timescale) would be tricky.

Intelligent controls with weather compensating flow temperature control &/or temperature sensors in the slab should minimise any overshoot & allow predictable behaviour. However, the occupants will have to be trained not to use the thermostat like an on-off switch.

David]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95301#Comment_95301 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95301#Comment_95301 Fri, 26 Nov 2010 21:48:04 +0000 djh Posted By: wookeyAnd I've seen people polishing their concrete in order to use that directly as the floor surface. Is that expensive (this is a relatively small 28m2 area)?
No, but I've also read that it's not as cheap as you might think as well!

Nick Grant described his on the AECB forum - http://www.aecb.net/forum/index.php?topic=35.0

I'm sure I have some more links somewhere but I can't get at them at the moment. Anyway the photos at the top of this page - http://www.concretenetwork.com/staining-concrete/ - and in the linked photo page give an idea of what you can do.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95308#Comment_95308 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95308#Comment_95308 Fri, 26 Nov 2010 23:17:15 +0000 Viking House Here's a new detail we're using for a Passive house renovation and new build that may be of interest. The 500mm of stone in the foundations is used as a cheap inter-seasonal store, it will be heated by solar from Sept to April. If it works we won't need supplementary heating and the stones are 100 times cheaper than a water store.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95312#Comment_95312 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95312#Comment_95312 Sat, 27 Nov 2010 01:54:58 +0000 wookey
I was considering 10mm of acoustic foam between screed and slab but had mostly decided that in summer it would just isolate the slab unhelpfully and I was probably better off without it. It would be nice to be able to model this properly and not just guess.

I quite agree that in normally-heated areas we'd want fast-acting heating not really-slow heating.

Oh and whilst we are on the subject is 'less un-green' (i.e high PFA) concrete fairly standard now or am I going to have to search it out and pay extra?]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95342#Comment_95342 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=95342#Comment_95342 Sat, 27 Nov 2010 17:22:04 +0000 jamesingram Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=204579#Comment_204579 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=204579#Comment_204579 Sun, 29 Jun 2014 02:28:17 +0100 BJC
From COLD, it takes 3 days of log burner (16kw max) to get the 20 tons of deep concrete, UFH up to a 35 deg return temperature.

Then simply measure the slate temperature with an IR gun (thermometer), turn on the pumps to measure the deep heat in the slab and top up as needed.

In worst weather that's an 8 hour burn in the snug every afternoon / evening.
Our logs, coal in desperate times.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206243#Comment_206243 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206243#Comment_206243 Wed, 30 Jul 2014 19:04:19 +0100 Shevek
Polypipe suggested plastic formers but I don't want to use anything that will insulated the pipes from the slab.

I was thinking of using clip rails but they still need to be fixed to the slab somehow.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206251#Comment_206251 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206251#Comment_206251 Wed, 30 Jul 2014 21:51:03 +0100 djh Posted By: ShevekI'm also looking for a way to connect UFH pipes directly to a slab. None of the UFH systems a designed for this. They all assume either insulation or suspension between joists.
Eh, I'm no expert on this subject but fastening UFH to the reinforcement in the slab is surely a very common situation?

Or are you saying the slab is already poured? In which case I suppose embedding the pipes in a screed would be the way to go.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206252#Comment_206252 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206252#Comment_206252 Wed, 30 Jul 2014 22:03:49 +0100 Shevek
We have screed and battened timber flooring. But even if embedding in screed we still need to fix it in place before screeding.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206257#Comment_206257 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206257#Comment_206257 Wed, 30 Jul 2014 22:31:25 +0100 jamesingram A98 or A142]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206258#Comment_206258 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206258#Comment_206258 Wed, 30 Jul 2014 22:32:50 +0100 jamesingram Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206265#Comment_206265 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206265#Comment_206265 Thu, 31 Jul 2014 08:03:40 +0100 Simon Still
I can't imagine you'd need that many screws as the clips don't look like they hold to the insulation very tightly normally.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206267#Comment_206267 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206267#Comment_206267 Thu, 31 Jul 2014 09:07:20 +0100 Shevek Posted By: jamesingramhow deeps your screed . lay a light mesh on top of slab and cable tie to this
A98 or A142
Yeah that still leaves the battened timber flooring to deal with though.

Posted By: jamesingramremember to fill and pressurise ufh pipe work before you screed.

Thanks!

Posted By: Simon StillCan't you use the cliprail and drill/screw it to the concrete slab through the holes that would normally take the staples into the insulation?

I can't imagine you'd need that many screws as the clips don't look like they hold to the insulation very tightly normally.

I think this will be the way.]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206336#Comment_206336 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206336#Comment_206336 Fri, 01 Aug 2014 07:47:36 +0100 Triassic Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206345#Comment_206345 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206345#Comment_206345 Fri, 01 Aug 2014 10:26:27 +0100 willie.macleod http://www.floorheating-direct.co.uk/products/45-1-water+heating+insulation/51-1-fixing+rails+and+hammer+clips/p-36-floor+heating-direct+plastic+hammer+clips]]> Fitting UFH on/in concrete https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206495#Comment_206495 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6598&Focus=206495#Comment_206495 Mon, 04 Aug 2014 07:23:53 +0100 alec
If you are going to use water approaching ambient temp you can get away with less insulation.]]>