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Retrofitting UFH with suspended timber floors - advice - Green Building Forum


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Retrofitting UFH with suspended timber floors - advice

Hi folks, this is my first post, after lurking for a while getting some hints and tips ready for when I come to do my own renovation. I am just about to embark on that journey and have a few ideas that I'd like to put out there for some feedback. Really appreciate any input, and apologies if anything I ask has been answered previously, I promise to have a good search through before I post anything.

So the story so far is, the house I am buying is a former bungalow, I am initially renovating the ground floor before moving on to upstairs. I am looking to install underfloor heating and am concocting a plan which I would be grateful for some feedback on, but there are also a few queries I have.

My plan at present:

Lift all the floors
Install battens to support insulation
Lay a thin foil type insulation between each joist
Press down 75mm polystyrene boards Inbetween the joists (the plan is to substitute foil backed kingspan with the foil insulation roll + polystyrene sheets & reduce thermal bridging across the joists, the polystyrene is simply to reduce cost)
Run underfloor heating pipes and secure to insulation - pipes to remain below the line of joists
Fit a layer of welded mesh over the top - to increase strength of screed mix
Secure mesh using battens fixed perpendicular to existing joists at approx 1metre centres
Mix screed 4:1 sand:cement and apply to flooring
Screed thickness from the top of the perpendicular battens to the polystyrene boards will be approx 50mm

Does this sound OK in terms of materials?
Will the screed itself be strong enough to provide support for walking on etc?
Should there be an additional layer for strength or will the screed (reinforced by the mesh panels) be adequate.
The flooring is a huge expanse covering the entire house for what is essentially a continuous layer of cement, does this need to have some form of seperatin up to all for expansion etc or will he regular temp of the house be adequate?

The house downstairs floor area is approx 160m2. In the near future I will be taking measures to try and make the property as airtight/efficient as possible

Really appreciate any thoughts you may have


  • 50mm screed is going to be heavy.  I'd worry about the strength/bending of your joists, unless they're continuously supported on a subfloor.  And sagging joists will make your screed crack.

    Bware that adding a little bit of welded mesh on top isn't going to make the screed work like reinforced concrete... you'd need the reinforcement on the bottom (so its in tension) to do any good, and my gut feel is that 50mm is too thin for a long span. 
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