My Journey into Retrofitting Underfloor Heating

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14 Oct 2011
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We recently bought a new to us house. It’s probably our last house before either a wooden overcoat or something worse……an old persons home! Anyway, the original house was built in the 50’s and over the last couple of years was completely modernised and extensively extended. The walls are all insulated, the roof has a about a meter of insulation, it’s triple glazed throughout and the extension floor is fully insulated. We were not sure what had happened under the original house floors. All houses have some compromises when you buy them, we wanted a house close to a good town / village (1 mile max), with no immediate neighbours (so I can’t play in the workshop without irritating anyone), enough ground that I could build a large workshop or had a building suitable for one, good views, south facing and reasonably modernised, and affordable. That limited what we were interested in. The big compromise with the house we have bought is it’s larger than we wanted and needs changing to meet our requirements, however, the extra space will we believe come in as my parents now well into their 80’s will some day very soon need assisted living. They will move into the spare bit of the house.

The kitchen dinner are had UFH (under floor heating) already installed and is right in the middle of the house. We didn’t want to tear out the kitchen and everything else in order to install UFH throughout the rest of the house. This has led to some pondering of how to achieve it without having different levels on the ground floor, something we did not want as we are planning for the future it has to be wheel chair / limited mobility friendly.

The upstairs is a suspended floor, joists and floor boards. The original plan was to lay the UFH heating pipes on top of the floor with a screed covering, this would increase the floor height by 25mm, something we could live with without altering all of the door lintels. However, the house is very long and actually dips either end from the centre. Something we did not realise or even consider initially. It was realised only when one of the workmen said that self levelling screed can only be pushed to give a gradient of around 5mm…….otherwise it will fully level the upstairs. A quick laser level check and sure enough, the house dips nearly 40mm at either end, which would compromise the door lintels by nearly 65mm, which is too much. The options were either to lift every door lintel, or find an alteration solution. The options were lifting all the floors and putting the UFH under the floor or an over board system thats laid over the existing floors but does not need a screed. The cost effective solution, which had the least compromises was to go for a board system. There is a small reduction in heat transfer compared to screed, but not enough to justify the additional expense. This increases the floor height by circa 20mm.

Downstairs, that required a bit of creativity!
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The downstairs is a story of two halves, one side of the house is ‘new’ and the other old. The new side presented initially the biggest headache. It’s concrete / screed over insulation. So keeping the floor level with the kitchen was potentially a real problem. Initially we could only think of two solutions, the fist to place the UFH over the existing floor within a new screed which raised the floor level, or dig out the existing floor a replace with new. Neither option was really what we wanted. A bit of digging suggested you can actually ‘route’ out the oath for the UFH pipe work into the existing screed floor. Interesting. A few company’s I found will do this, however I wanted the same plumber to do everything to avoid any issues if it didn’t work……nothing worse that trying to allocate blame! I found that yoi can actually hire the routing machine very very cheaply, and I do mean very cheap. So, the plan was to route the floor ourselves and lay the pipe, with a thin layer of screed over the top.


The room is large, and requires around 400m of pipe laying within the floor, that’s a lot of grinding. First stage was to check that the previous builder had built the floor properly. I didn’t want to go to all the effort to find that tgere wasn’t the required level of insulation in the floor even though I had the building sign of certificate. I know of buildings being signed off and the inspector only visited site twice!

I drilled a hole in the floor down to the DPM which will cover the insulation to check. Yes I know I’ve punctured the DPM separating the concrete from the insulation which I will repair, but I didn’t puncture the lower DPM that separates the insulation from the outside world.

Next came days of grinding, initially I didn’t know you could hire the ‘correct’ extractor for the grinder, it only stated it came with bags. Anyway, the bags it comes with you can forget, so we tried a couple of dust extractors. That led to two very dead dust extractors! The ground screed comes out hit, hot enough to melt standard extraction tube and the very fine dust soon destroys the bearings in the extractors. Going back to the hire company, and this time talking to another person, they suggested I hirecthe extractor for the unit. FFS!! which is also very cheap to hire. So here are the machines

The grinder is just that, a 2.2KW motor attached to a wide diamond wheel…..Oh, they don’t tell you it’s 16A when you hire it, but that for me was easily solved. Now, tackling this job is nit the feint hearted, it’s very strenuous hard work. Ee ground down 20mm, and it’s very slow and needs two passes, each 10mm to get it to depth. You really have to lean on the machine to move forward. the machine instructions says it can’t do curves, and it’s dimensions limit how close to the edge you can get. The ‘return’ at the end of each loop we hand ground in with a hand grinder……that was a thankless task.

Would I recommend doing it yourself…..absolutely not. Although I personally did around a third of it, I also paid for 8 man days of labour to do it with me. When I now reflect on the costs, it would have been far more cost effective to get a specialist company into do this section of UFH. This is where we are now at, the pipes and screed will be laid in the next few weeks.
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The other ‘wing’ of the downstairs is the old house. This is again a suspended floor. I decided we would lift this floor and out the UFH under the floor boards. There are three rooms that need to be

A good friend helped me with lifting some of the flooring, the big yellow bar in the forefront is his. Hopefully he will chip in and tell yoi exactly what it is…..all I can say it that it’s brilliant for this kind of job.

The floor boards are held down by the old forged nails, so they really really hold. We destroyed Al, the floor boarding as a consequence getting it up. That was a real shame. Two of the rooms were suspended flooring, but like all renovations, you get surprises. The third room was a thin layer of concrete laid over sand, no DPM, so up it all had to come.


I have two ‘apprentice’ who like to inspect the work, the white one is the youngest and most mischievous.

the floor will be rebuilt and will have in this case UFH built into it.
The two downstairs suspended floors need insulating before the pipe work is laid on top, a loose screed will then be added before floor boarding goes over the top.
This is one of the two rooms ready for the pipes to be laid. We are installing a lift as my father cannot any longer negotiate stairs. The foreground hole is for the lift pit that needs building. This will not only serve his needs but also future proof the house for ourselves in the future. The other small hole is so I can access the underfloor if needed in the future.

WOW. Amazing work. I'll be watching this thread for updates, really interesting project you have going on. Keep up the good work
Personally I would have looked at breaking out and re-laying the screed because that way the slab is on the pipes and acts as a heat mass whereas your pipes are sitting on the slab, you will get faster response in that it will give heat quicker but it will also drop quickly. You also have the issue of no insulation under the pipes, maybe you could have ground more of and used the insulation boards with the pipe grooves in them but probably too late now.
Hi Roy, I think if I were to go back with hindsight I would dig the screed floor up too.
Yes hindsight would be such a great gift, how many jobs have we done where afterwards we standback and ask ourselves why did we not do it this way instead but then would we learn as much.
Looks like a very interesting project. I recently went through this with our house. Having moved in we moved out again 18 months later, then moved back in six months later. It's like moving three times. Installing UFH is a complete PITA but the end result is worth it, as I think it's a very efficient way of heating your home vs radiators and you gain all the wallspace they occupy. It has completely transformed the nature of our home - it was cold and damp before - now dry and warm.

For us we had to dig out the entire ground floor to a depth of around 300mm. I ended up paying almost as much for this as for the UFH system itself. I could have got it done much cheaper but we had a tight schedule and one team pulled out at the last minute and I had to find an emergency replacement which cost me a King's ransom. Anyway, it has meant that the entire ground floor is level to a tolerance of 1mm except for a small slope at the back door. This is important since the original floor was a complete mish mash of levels; in one place there was a huge step on which the previous owner fell and nearly broke his back, confining him to live downstairs.

We went for Geocell insulation for it's breathability, a breathable membrane under that and on top. Speedfit UFH and a limecrete floor, laid by the Limecrete company. On top of this we are laying Norfolk pamments and other tiles.

Good luck with your work.
To answer an early question, the pipes under the landing were not at the time connected up, that still needed to be done and is nor ongoing. We decided to get everything ready for an Air source heat pump (ASHP), and part of that was relocating the hit water tank down stairs under the stairs. The air source heat pumps, which we will need 3phase to power up, will be located outside right next to where the hot water tank is located…..the plumbing isn’t completely finished yet around the tank.

Make sure he uses some form of bracket on those expansion vessels, they look around 18 litres each and not good to expect the pipework to support them once they are partially filled with water. Apart from that it looks like a neat job and I assume it will be down to you to build a cupboard around it.
Thanks Roy for the heads up, the expansion tanks are on their own mechanical supports.
You must have the ones with the fixed brackets, a lot use a bracket and bandclamp which I did not like so I fitted my two using a wooden frame that they sit in and supported by the flange . That cupboard will be a good airing cupboard when finished.
Interesting post - thanks for sharing.

Do you have a 3 Phase supply already? Are you going for horizontal or vertical loop?
I have a quote for 3ph for the workshop and I’m waiting for one for the house.
Im not sure what your asking when you say is it horizontal or vertical loop?
I have a quote for 3ph for the workshop and I’m waiting for one for the house.
Im not sure what your asking when you say is it horizontal or vertical loop?
Sorry, I must have misread it as I thought you were going for ground source but see it is air source.

We looked at ground source but were dealing with Japanese knotweed at the same time which made a horizontal loop impractical and a bore hole for a vertical loop seemed ridiculously expensive at the time. I wish we’d done it now.
What a journey

we went down the thin bed underfloor system on top of the existing power floated slab - so no screed - and thin foil insulation less than 25 mm overall thickness and very effective

It’s been a while, but the UFH is again starting to make progress. There was a lot of other jobs that have needed to be done befire the floor was effectively sealed up.

The main lounge where we ground out channels for the pipe to sit in, now has the pipe fitted. That went very well and was easy to do. The pipe is temporarily held in okace by metal straps screwed down over it. It’s now ready for a layer of screed on top.