Ground floor UFH installation - Screed / Insulation Questions

[Nick Pain]

Hi All
We are renovating a 1980s built house and intend to fit UFH throughout.

In the existing part of the house the floor is made up of 4" of hardcore, DPM layer, 4" concrete with 2" screed over the top.

Given that there is no insulation in the existing floor will overlay UFH in EPS panels work ok or is the heat leaching into the uninsulated existing floor going to make it inefficient / ineffective?

Would I be better off removing the 2" of screed and lay 50mm EPS panels with the pipe routes cut in them for the UFH, then put 20mm dry screed boards over this then the engineered timber on top of that.

If anyone has any advice I would be most appreciative!

 

[tomfe]

Without any insulation / minimal insulation then your ufh will not be very efficient. It'll still work but will cool down quickly after it's been turned off so you'll have to run it for longer.
The thickness of the thinlayer eps panels are quite small so the benefit is also small.
If you can get more insulation in the better, you could use a polyurethane/polyisocyanurate insulation with the thinner ufh board ontop, then use a latex self leaving screed ontop.

 

[mointainwalker]

If you are confident enough to fix the pipes ( with wires) to the underfloor insulation then you will save a lot of money as the manufactured UFH boards are very expensive for the insulation value. The only problem is that it is not particularly easy to wire into the base insulating foam layer if you are using polystyrene.

 

[Nick Pain]

If you are confident enough to fix the pipes ( with wires) to the underfloor insulation then you will save a lot of money as the manufactured UFH boards are very expensive for the insulation value. The only problem is that it is not particularly easy to wire into the base insulating foam layer if you are using polystyrene.

I am happy enough to do that no problem but what do you suggest I put over the top of the pipes then? I would need at least 50-70mm if I use conventional screed or maybe 30 using a more modern one.

 

[mointainwalker]

Since you don't talk about height limitations, you have to consider efficiency, cost and whether you are doing it yourself or sub-contracting it.

Traditional biscuit-screed (min 65 mm ) is the only reasonable DIY option, but gives you much less mass- and a less level surface - than a 50 mm pumped anhydite self-levelling screed, which will also cover the outer surface of the piping much more completely and thus give you better heat transfer and better heat-storage because of the greater density. If you chose this variant, look for a mix* that doesn't require "polishing" after 24 hours to remove the layer of laitance: this creates a lot of dust and the extra visit by the contractors obviously increases the total cost.

I don't know about screeds requiring less than 50 mm min. thickness. It's been a few years since I did mine. I don't live in the UK so this may be of no direct help, however I paid about £ 25/m2 for my floor ( 120 m2 ) of 55mm with a flatness of around 1 mm per metre ( specification was 2mm /metre ).

*At the time there was one producer/patent holder of this that I found and it was a German company which obviously had licensees in different countries. I have no idea what the situation is now