I am installing ufh in my (tiny) house conversion. The total area is 22 square metres, and will be a tiled living / dining / kitchen area. Since I’m also laying the floor slab I have the option of placing a reinforced 100mm slab on top of the insulation (250mm eps) incorporating the ufh pipes instead of the conventional 100mm slab, insulation and 65mm screed method. Building control have OKed this.

I’ve investigated pumped screeds and ruled these out due to the expense on such a small area, so my question is, how much will the ufh performance be affected by being laid in a 100mm concrete slab versus a 65mm screed? Ufh manufacturers imply slower response times would be a problem, but I’m interested to hear from someone who’s actually done it – my builder seems to think it won’t be an issue, and the ease of one lot of concrete being laid rather than two is attractive. However I won’t have a secondary heat source to supplement the ufh so I want to be sure it’ll be affective and reasonably controllable.

If I go down the conventional slab and separate ufh in screed route, how long would I have to leave the slab to cure before laying insulation and screed on top?

Many thanks in advance!

Comments
  • Rachel Haynes

    Hi, I would always recommend you speak to the UF heating manufacturer as you have.

    Putting UF heating in a screed or concrete based floor with

  • J F

    Many thanks for your advice; you’ve pretty much confirmed the advice I’ve seen elsewhere. Aside from the additional cost my main issue is time since my build schedule is ASAP!! So how long would a 100mm slab require to cure prior to adding insulation, ufh and screed? And then how long before I can tile, bearing in mind it won’t be a liquid screed thanks to the cost! Thanks again.

  • J F

    Many thanks for your advice; you’ve pretty much confirmed the advice I’ve seen elsewhere. Aside from the additional cost my main issue is time since my build schedule is ASAP!! So how long would a 100mm slab require to cure prior to adding insulation, ufh and screed? And then how long before I can tile, bearing in mind it won’t be a liquid screed thanks to the cost! Thanks again.

  • Rachel Haynes

    Hi, difficult to say definite times without getting into detail on your programme and build method. Regarding the slab, on all the sites we have been involved with involving UF heating the slab has been poured within the first few weeks of the project and the screed has gone down a few months later (larger projects) – this is not to do with curing and drying time but with the length of time is takes to do all the other elements of the build you need to do before you can think about laying a screed – i.e. getting the building water tight so walls, roof, windows etc. To get the exact time you should leave the slab "open" for to cure do speak to the concrete supplier or whoever is specifying the concrete mix as this will have some bearing on the curing time.

    For screeds – this is trickier (sorry). You should leave a screed to dry fully before sealing it (such as applying vinyl or tiles) and the rule of thumb is that a standard sand/cement screed takes a day to dry for every (mm) of screed depth (65mm = 65 days). Be aware that some thinner screeds that are chemical based will actually take longer than a water based sand/cement. There are also quick drying screeds supplied by specialist suppliers – but with any of these you would need to discuss the drying time necessary before laying floors with the screed manufacturer. Specialist screeds can be more expensive but can possibly save money in the long run by saving time.

    Lastly, there are products that can be used to seal a screed to allow flooring to be laid sooner, but again this needs to be discussed with the screed supplier or a specialist liquid seal supplier. There are a lot of them out there on the web and their technical departments will be a lot more specific than I can be.

    A lot of flooring suppliers will specify what moisture content the screed needs to be at to lay the floor – don’t be tempted to lay the floor until the screed is dry enough.

    As you are using a builder ask him to programme the works (if he hasn’t already) so you can both be sure what should happen when and that there is enough time allowed for all the trades. Get him to talk you through it and discuss the options open to both of you if you need to save time/cost.

    Hope this is of use.

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