How to turn a lovley old house with solid walls into a warm efficient home



First floor ufh

When designing the heating system I was always concious that I wanted to run the CH water temperature as low as possible in order to maximise efficiency of the heat pump. I chose for my first floor to use radiators in the old part of the house as they have old elm floorboards that I did not want to mess with. For the extension, however, I did want to put UFH in my en-suite and bathroom as I felt a warm floor would be a nice feeling for those rooms.

I was frustrated when I saw other people doing first floor UFH and suspending their pipes in aluminium spreader plates then on top of that laying 22m chipboard and often on top of that another 18mm of engineered board. That is 30mm of poorly concucting covering to the pipes. I figured that though heat would get through I could keep my water temp lower if there was less resistance the thermal transmission over the pipes.

After much deliberation I came up with a plan and set about being a little experimental and doing things 'my way'.

Routing floorboards, eco, renovation, home, greenMy plan was to have as little thermal resistance between the ufh pipes and the floor surface so that even with comparatively cool water flowing I would feel a reasonable warmth to the floor. First off, therefore, I did not really like the idea of 22mm of chipbaord flooring between my pipes and the floor. I have seen systems where in stead of using aluminium spreader plates beneath the floor you can make a tray between the joists and fill these with a sand / cement mix, offering some mass to the floor. There is still an issue as to what you cover the pipes with - chipboard again?. There is also an issue that all the joists need to be notched in order for the looped pipework to run between them. 

I liked the idea of cement boards as these offer little thermal resistance. However, cement boards alone are not up to the job or an acceptable substitute for chipboard flooring. I concluded that if layed chipboard but routed out channels at 200mm centres at 90 degrees to the joists then I could lay the aluminium spreader plates on the top surface of the chipboard, over which I would lay thin cement board. As I have floor joists at 400 centres and the joists are 75mm thick they are quite closely spaced, which I felt would help if I were concerned that routing out the boards woudl weaken them. The only thing to do was to do a trial and make a judgement, so I routed out a couple of sheets of chipboard flooring and laid them.

Underfloor Heating, eco, green, renovationRouter jig, eco, home, renovationI made a jig so that it slotted into each routed groove in turn and by routing along its edge I would be creating slots at 200mm centres for the spreader plates to fit in. I also made a jig to rout the loops for the end. A simple piece of acrylic cut out to allow a 25mm guide bush and a couple of pegs to locate it in the ends of the routed slots meant I could accurately cut a routed loop at each end. I cut them so the end of the loop was over a joist, whcih meant the boards were supported. It was a little laborious, but with vacuum extraction on the router and a little patience I cut a series of slots and loops with an 18mm cutter.

As my UFH pipe is 16mm I cut 18mm slots into which the spreader plates snuggly pushed. The pipes then fitted tightly within the plates. I was very impress how strong the floor remained even without the cement board over the top. All felt very stable and strong with no bouncing. I am sure my wide joists and close spacing of them was a large factor in this, so I would not be comfortable recommending this system as other people's layout will be different. If this is something that interests you then you have to make your own judgement. However, I was confident that it all felt very good, so I went ahead and routed the whole floor and laid the pipe work.


Over the top of the pipes I planned to lay cement board. No More Ply supply boards in 6, 9 and 12mm thicknesses along with a polyurethane glue for overboarding floors (much as we would once have done with ply) The cement board has a good thermal transmission and is also a better option than ply these days as, should you have any bathroom leaks of any sort it does not deteriorate like ply does. I was comfortable that a 6mm board would be sufficient. In truth, much of the strength of the overboarding comes from the polyurethane adhesive, but they would be bonded and well screwed down (making sure not to screw through the pipes!

Vinyl floor ufhOnce the boards were fixed down the floor was strong and smooth, ready for my floor covering. Once again, to easily allow thermal transmission I did not wish to lay any kind of wooden board. I chose to lay vinyl tiles. I have used wood effect Karndean vinyl on a few floors now as at only 3mm thick it does not 'block' the heat from the floor. It is true there is some compromise - I do realise that an discerning eye will be well aware it is not real wood. However, I think they look very good, feel good to walk on and are an acceptable compromise to achieve my goals.


Vinyl floor showerI think the floor looks and 'works' really well. As discussed in my heating system article I run my UFH very low at 28 degrees. The floor is just nicely warm, not hot and the room is toasty too.

Rather than buy a shower enclosure I designed my own and had glass cut to my specifications. I made the shower totally frameless by devising a way to continue the brick corbelling from the old back of the house prior to the extension and had mitred glass cut. I am quite pleased with the shower as well as the floor. I used the same technique for my en-suite floor and it all works well.

Note: This approach was my own idea so if you choose to do similar you do so having taken responsibility about structural integrity and suitability.



© Christopher Thompson