Sorry, another UFH question!! I originally posted this on the 'other side' too but got a lukewarm response, so hoping someone on here could assist.

Renovating/extending 1950s bungalow. Will end up insulating where I can (EWI, loft >400mm), 3G windows/doors, but no way passivhaus! Looking at my UFH options (retrofit spreader plates or screeded.

Condensation internally has caused most of the parquet floors to buckle up. I was going to use one of the retrofit UFH spreader plates on top of the parquet tiles (act as a bit of insulation) but now that they've decided to come up, I've also seen what appears to be a 20-30mm screed layer on top of the uninsulated concrete floor. Some of this is cracked and comes away easily from the concrete.

As the slab is currently uninsulated I would favour getting at least some insulation in there (50mm) before I put UFH in. Better than nothing! I can't go more than 50mm and I realise a high% will be lost keeping the worms warm! Ceiling height is currently 2460mm and I am willing to increase all doorway heights. I don't really want to lose more than 180mm (I hate the ability to be able to touch ceilings with the use of a stool!).

If I remove all screed (80sqm) I may end up with a bitty and very likely uneven concrete floor. Can I put insulation on the rough concrete? I didn't want to go down the self levelling compound route or put in a new screed with insulation on top of that. Can I get away with putting down a sand binding layer (with ant powder) and then lay insulation boards on top of that? If the concrete floor doesn't have too many depressions can I just lay insulation on top without sand? I assume if there are areas where the insulation boards aren't 100% level (but with no voids beneath) then as long as the screed is levelled properly I should have no problems? Worst case is that the screed may be 3-5mm deeper and result in a slightly different temperature heat zone.

Option 1: Screeded UFH
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Seeing I will be going to the effort of removing the old screed, I am now thinking a screeded UFH option may be the way to go if I can use a minimal height screed:

20mm floor tiles
75??mm screeded UFH
50mm insulation
30mm sand/cement/ant powder (if needed)
Existing concrete slab

I've read on here that a liquid screed isn't the best to use. So if I use standard sand/cement mix (with fibres) can I get away with less than 75mm depth?

Option 2: Spreader plates UFH
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Alternativley I could use spreader plates (GBP38/m2 supply only):

20mm floor tiles
22mm ply board
25mm spreader UFH plates
50mm insulation
30mm sand/cement/ant powder (if needed)
Existing concrete slab

I save a bit in the height with this option, but I suspect it won't be as efficient thermally. I also have concerns with bounce factor with the spreader plates sitting on the insulation. And obviously the heating itself willl be a bit more responsive but also cool down far quicker.


Grateful for any answers / opinions to the above questions/options.

''I originally posted this on the 'other side' too but got a lukewarm response''.

Isn't that what you want from UFH?

Ps 38 quid a metre is insane money. Wunda trade do them for more like 4?! Makes me wonder what you're paying for the rest of your gear..

Nah, £26 for that is more reasonable. I got mine for £20 from the company that poured my screed, and when I looked at the maths it was about £10sqm for materials and £10sqm for fitting. Given that a few monkeys and a few hours saw it finished, in one sense it was expensive but in another sense it was a job off my list (and there are a lot of jobs on my list) and relatively cheap. If doing it over, I'd lay it though 2 people really helps, one to unfold and walk the pipe into shape and another to follow on with the stapler. https://www.youtube.com/watch?v=5mrUxAI2PVA is a slowed-down version of what actually happened on site


Wunda's spreader plates for £4 are the aluminium ones, circa £2 for a 1m by 0.5m sheet of alu with a groove in. You wouldnt lay them on a floor like you have, but theyre what I think of when someone says "spreader plates"

You don't have to take your slab up if you don't want to, but something will have to give - you either accept a large buildup, accept a loss of insulation, or accept a weekend's pecker and digger/dumper hire and get mucky. I didn't take my slab up, but i was building a house inside a warehouse and had the height to play with/could set my levels. With 175mm of PIR I'm now left with quite a considerable step up into my front door. It was a choice between build the 8sqm lobby up and cut the bottom off the lobby doors, put steps in the lobby or take out 300sqm of 6 inch slab to make it all level..

90sqm, honestly, you'll do it in a weekend with 2 of you, a 3 ton mini digger and pecker (can you get one in?) and a baby dumper. See if someone wants the hardcore locally too - farmer perhaps

Posted By: cjardNah, £26 for that is more reasonable. I got mine for £20 from the company that poured my screed, and when I looked at the maths it was about £10sqm for materials and £10sqm for fitting.

Aahh. okay so you had the genuine article at£20/sqm, i.e. screeded UFH rather than retrofit/overfloor/spreader plate. My price was for overlay system (spreader plate?) ontop of the slab.

Posted By: cjard
Given that a few monkeys and a few hours saw it finished, in one sense it was expensive but in another sense it was a job off my list (and there are a lot of jobs on my list) and relatively cheap.

Yes, I know what you mean. I don't have a list anymore. I have a book. And a new edition comes out every few weeks. So your £20 cost was for UFH plus the cost to screed it? Or screeding was included?

Posted By: cjard
You don't have to take your slab up if you don't want to, but something will have to give - you either accept a large buildup, accept a loss of insulation, or accept a weekend's pecker and digger/dumper hire and get mucky.

90sqm, honestly, you'll do it in a weekend with 2 of you, a 3 ton mini digger and pecker (can you get one in?) and a baby dumper. See if someone wants the hardcore locally too - farmer perhaps

Think it will take me a while to dig out with a jack hammer type thing. No chance getting a min digger in there. But yeah, something I could do in the NY to keep me warm. I'd prefer decent performance from UFH when it is sourced from ASHP rather than taking the 'easy' way out no and using an overlay system. Costwise to dig out and screed may work out cheaper also. And at least I would feel more secure that the UFH will work! I just have concerns about digging out 175-200mm and damaging founds/walls or finding bodies

Thanks for those costs. It would be cheaper then to go for an overlay UFH system then at £26sqm. But that will be a short term gain.

Okay, went ahead and managed to take up some concrete. This area is only 100mm thick (no DPC) and dampish soil underneath (not any rubble evident either). So if it's all 100mm thick then it's an easy job to lift all 90sqm. However the external ground slopes down towards the rear of the bungalow so I expect at least some fill/rubble or thicker concrete that end of the house.

My plan is to dig up all concrete and then determine how much insulation to put down. I'll dig up and remove the soil and then fill floor area:

Screeded UFH (75mm)
VCL
Insulation (150 min hopefully)
DPM
compacted hardcore (the stuff I've just lifted!!) and sand blinding

Would that work? I don't want to concrete floor and then have a seperate screed just for the UFH.

How are you taking the floor up next to the walls so as not to damage the wall. Have you used a concrete saw to cut through the floor 100mm in from the wall?

Posted By: tonySledge hammer will get that up, take screede off first

Think I will Kango it so I can break it into smaller bits and then whacker it down as my base (once soil is dug out to a decent level).

Posted By: DantenzHow are you taking the floor up next to the walls so as not to damage the wall. Have you used a concrete saw to cut through the floor 100mm in from the wall?

I'll just carry on from where I started with this trial hole, gently breaking away from the wall. It should hopefully just pull away from the wall with a little persuasion. And I'm hoping all internal walls carry on down and weren't built on this 100mm concrete!

Prop it as you go well solid off over site fill and do thickened up slab and build up to the underside off that later

There have been problems with liquid screeds cracking, best to avoid potential problems if possible

If you're going to put a nice big shagpile on top of your floor, why are you go concerned about a few cracks? Not sure if I understand the logic of using a thick carpet to attempt evening out a slab that is like a motocross course but not one that is millpond flat with an occasional gap

Posted By: kentishgreenIt was my attempt at a joke

I think the smiley might have been a big clue ....

Thanks Rex,

I've started digging up the screed (not too bad so far) and will hopefully have the 100mm concrete dug up some time in january. So will lay the pipes in my new concrete floor...so hopefully no creaking for me. Well only my back perhaps....

I'm doing a similar job on my refurb. I've chipped out the existing screed, ground that flat. Looking at celotex ufh insulation 70mm thick. Then using a gyvlon liquid screed. It's meant to be the business for ufh!