Specs for a new floor in old house (building content)

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  • Specs for a new floor in old house (building content)
  • So.. House we are purchsing has active sulphites in the infil material below the concrete so has to be removed down to 800mm below current floor level.

    So I want to put in a underfloor heating system, speedfit for example. I want it to be insulated and have been reccomended 100mm of kingspan or equivalent. 50mm of liguid screed to cover the pipes and then maybe karndean above.

    What im not sure is the make up of the rest of the floor. Dolomite, sharp sand blind. DPM insulation,concrete, insulation pipes then screed.

    Confused really. Any help would be appreciated. Obviously working to building regs. Its the complete downstairs of a semi.

    Ive spoken to 4 builders and each has a different idea on the make up of the floor. They are more the traditional style of builder. We dont have a big budget.

    Cheers chaps

    Dig out 800mm Oli and then just fill with this:

    Can I come around for the first play?

    Bloody hell 650mm is a lot to make up …..what’s the sqr footage ?

    Cheers Dave 🙂 Great idea!!


    so working down

    50mm liquid cemex screed with UFH pipes
    polythene protection layer 125 micron
    100mm Insulation foil backed Kingspan style
    100mm concrete
    DPM 300 micron
    50mm Sand???? Blanking layer? not sure of depth (estimate) 3 tonne?
    500mm Dolomite approx 44 tonnes

    Sounds about right! Based in North east if any one knows of any quality suppliers with sharp pencils.

    Tbh I wouldn’t bother with sand bellow the concrete …just go for ballast …

    You could see if you could save a bit on the insulation thickness. The u-value achieved can be calculated by Kingspan or an equivalent to then be compared against the building control reqs. They will need to know the floor area and perimeter of external wall enclosing the floor. But make sure the underfloor supplier ok’s whatever thickness you put in so that you arent just wasting heat into the slab.

    singlecrack i assumed the sand blinding layer was to limit damage to the dpm? Is this not the case?

    Grunka.. Im going off a tech doc from a company called nu heat and kingspan. Ill look again but i would of thought 100mm would be fine. Should i go for more?


    In theory your sand is for that. However ready mix concrete is not that permeable. Few building controls pull you on it now. If it was going to be heavily trafficked prior to pouring then yes I’d go for it.

    I was actually thinking you could probably get away with less. Horses for courses but the last job I saw with under floor heating only had 50mm, but its all dependent on the size and shape of the area and the rest of the build-up etc etc.

    Google the kingspan website and dig around for their technical help line number. I’m pretty sure they have an option on it for domestic self-builders. They’ll be happy to advise at no cost as you’ll be more likely to spec their stuff if you know it works! And do check the heating supplier is happy with the thickness & product type just incase there are any funny compatibility issues for whatever reason.


    Why such a thickness of dolomite?


    No way would I use anything less than 100mm for underfloor.


    Can I just add that the British Standard for Levelling/Wearing screeds for domestic applications where the screed is floating (as in this case on top of the separating layer & insulation) advises a minimum screed depth of 65mm.

    It also mentions about crack reinforcement – usually a steel mesh placed in the middle third of the screed, however not practical with UFH so people sometimes go for a fibre reinforced screed. Just bear in mind the reinforcement isn’t to stop cracking but to limit the crack once it has occurred if that makes sense.

    You could possibly omit the sand blinding layer if you put the DPM on top of the slab although the NHBC stipulates that in this instance it would need to be a paint applied product, something Like LAC by RIW.

    Also if there is an existing DPM in the floor this may well be lapped with in the perimeter walls with the DPC – if possible try to get the builder to leave some of the DPC exposed form the wall so you can link your new DPM with it (this might seem a built belt and braces but that’s what I’m like)

    Also with underfloor heating it is best to have a thermally neutral floor covering tiles/carpet etc. If real wood, it may act as an insulator against the UFH meaning the system has to work harder. If you google it there are arguments for and against this principle.

    Obviously all the above is hypothetical and in no way to be construed as though I know what I’m talking about in any professional capacity.

    EDIT: of the ninja variety

    Premier Icon trout

    What are these active sulphites and what are they doing

    You could save a bit by using eurotherm, or celotex instead of kingspan. Both are foil backed but slightly cheaper as your not paying for the kingspan logo.


    150mm hardcore
    150mm concrete
    Dpm / radon layer
    150mm kingspan/ celotex or whatever
    Vapour barrier
    75mm screed
    Floor finish

    wrightyson. I have to dig out all the shale/sulphite. And get down to clay or uncontaminated which After a floor test seems to indicate 700-800mm. Obviously until we get down to the dirty work we wont know the exact levels. These are estimations.

    So the dolomite is to infill and make up the levels. I assume this is the best thing to do. Compact it every 150mm with a whacker.

    So 100mm or 150mm of foil backed insulation?

    The 50mm pumped screed was taken from a tech document so I assumed it was correct for regs. I agree with the depth for a dry mix, but Im looking at pumped.

    Theyre is a dpm already in the floor but I would imagine this will trashed when breaking up the current floor.

    Im looking at perhaps Karndean as it seems to be okay for UFH application. Im aware of the heat transfer issues associated with engineered wood. Tiles are great for the kitchen but not sure i want them in the living room 🙂

    Ill have a look at other brands, im not loyal to kingspan just want a similar “U” value

    Thanks for everyones input. Im all ears

    You’re welcome mate 😉

    Premier Icon nickjb

    Kingspan (or similar) is great because you get a lot of insulation for the thickness. If you are making up the thickness anyway it might be worth considering polystyrene. Iirc you generally need twice as much for the same insulation but its much cheaper. Might save a bit of hardcore barrowing.

    We put out concrete slab over the insulation. There are pros and cons.

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