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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorHoveTom
    • CommentTimeOct 31st 2019
     
    I’m renovating and converting a 1930's bungalow. I’d like wet underfloor heating throughout downstairs. The old suspended timber joists are presently uninsulated and have about 350mm spacings. There is one new room which a concrete sub floor. Low tog carpet and underlay in the living room and engineered parquet or porcelain tile for the same effect everywhere else.

    I’ve ordered two sets of sliding glass doors which already. One set is in the new extension so can be easily adjusted for with the screed. The other is in the living room, which will be carpeted and has an exciting suspended timber floor.

    I’m slowly going crazy trying to work out which is the best ufh system to use.

    1) Spreader plates (Cut to size to fit the narrower old joists )
    2) UFH Pipe clipped to the top of rigid insulation between the joists and just below and then Lytag poured in on top with a new subfloor on top of that.
    3) Insulated below, then a new subfloor, then an overlay system of some sort on top of that.
    4) Insulated below, then the joists battened just below the top and a new subfloor cut and put on the battens flush with the top of the joists. Then an overlay system put on top of that. No height gain..
    5) A precut and grooved chipboard subfloor with the pipes then placed in that and a 6mm ply placed on top of that to protect the pipes ( or possibly a few mm of self levelling screed )

    Advice appreciated,

    Tom
    • CommentAuthorcjard
    • CommentTimeOct 31st 2019 edited
     
    2, but why lytag? From what I read is it's kinda self-insulating because it's not dense, but you want something dense to serve as a heat buffer and to effectively soak up heat from the UFH pipes

    On your other notions:

    1- my spreader plates are far less effective than my liquid screed. I wouldn't use them again
    3- but then you'll need something on top of the overlay too? height gain
    4- not sure how the overlay proposal is "No height gain.."
    5- 9mm plasterboard laid on the floor might make for a better heat transmitter than 6mm ply
    • CommentAuthorHoveTom
    • CommentTimeOct 31st 2019
     
    Thanks for your response. I’ve heard Lytag does take longer to heat up but also takes longer to cool down so acts similar to a poured screed over a concrete floor.

    I agree with your comments, hence why my head is spinning. Regarding my option 4, I considered cutting 22mm chipboard and laying that inbetween the joists, battened from below. So that it sat flush with the top of the joists. So you are now starting from joist level but with a subfloor already built in. Then if I put an over lay system on top of it, this would only come to the same level as a sub floor laid on top of the joists.

    However I have no idea if the sub floor laid in this way is strong enough or will cause other issues.
    • CommentAuthorgyrogear
    • CommentTimeOct 31st 2019 edited
     
    How about (heavily) insulating the periphery of the underfloor void, and putting the UFH in an insulated slab poured below the joists. You have now brought the suspended floor inside the heated envelope...

    gg
  1.  
    HoveTom
    Are you wedded to your suspended timber joists? Since what you are proposing is going to involve significant disruption anyway why not go the whole hog and take out the suspended floor and put in an insulated slab to carry the UFH in the normal way.
    • CommentAuthorMike1
    • CommentTimeNov 1st 2019
     
    As Peter suggests, I'd personally ditch the timber floor and install a slab.

    Alternatively, once you're sure that the timber floor is well insulated and appropriately ventilated - it won't be easy to access it later - I might consider a minimal height UFCH solution right over the top of the existing floor surface; for example Uponor Minitec / Nu-heat LoPro come in at around 15mm thick. (I'm currently thinking of doing something similar in an upstairs apartment to keep the weight down, though haven't got round to checking if I can lay it over EPS).
    • CommentAuthorHoveTom
    • CommentTimeNov 1st 2019
     
    I looked at ripping out all the old floor and putting in a concrete slab but both my builder and I were surprised at the total cost once it was all added up. It’s around 100sq meters and it was difficult to justify all the extra cost to still have a warm floor at the end of it. From memory I think it was close to £10k all finished with the insulation etc (which I know I’d need either way) Especially as the labour associated with the suspended floor was going to be mine and effectively free.

    I have looked at lo pro but it’s pretty expensive, any overlay system is, coming in around £5k + compared to just around £2k for pipe and manifolds, then either sand/cement mix or Lytag. Factor in the insulation for the over lay and it’s getting expensive and closer the the concrete slab choice.

    At the moment I'm leaning towards battened insulation between the joists, taped down to avoid the drafts, pipe clipped on top and then Lytag poured over that with an 18mm ply subfloor.
  2.  
    Not an advert, just a satisfied customer but really worth looking at www.wundagroup.com for UFH. They've got all sorts of options down to 16mm overlay and when I installed ours they were significantly cheaper than the competition.
    https://www.wundatrade.co.uk/ if you want to price it up yourself.
  3.  
    Posted By: HoveTomI looked at ripping out all the old floor and putting in a concrete slab but both my builder and I were surprised at the total cost once it was all added up. It’s around 100sq meters and it was difficult to justify all the extra cost to still have a warm floor at the end of it. From memory I think it was close to £10k all finished with the insulation etc (which I know I’d need either way) Especially as the labour associated with the suspended floor was going to be mine and effectively free.

    If you are doing part of the labour yourself - what does the cost of the slab come out as if you take out the old floor and lay the insulation DIY and get the builder after that? Are you comparing like with like on the costings?
    • CommentAuthorPetlyn
    • CommentTimeNov 1st 2019
     
    There is an alternative to Lytag - recycled expanded glass beads. Not sue of the lambda value of Lytag but the beads have a value of 0.0661 but with the added advantage of not absorbing as much water as Lytag and with a high compressive strength. Unlike some other loose-fill materials, do not settle or deteriorate after installation as they are inert, non combustible and do not decay.

    We have a quantity remaining from our selfbuild if you have any interest and could send you a sample for consideration together with a spec sheet.
    •  
      CommentAuthordjh
    • CommentTimeNov 1st 2019
     
    Why would you want insulation around a UFH pipe?
    • CommentAuthorRex
    • CommentTimeNov 2nd 2019
     
    At the risk of loosing a bit of height, I would use Lewis Plates

    https://reppel.nl/en/composite-steel-floor-decking-systems/lewis

    I cannot find the link but they also do (or may be did) a system where the small diameter UFH piping is threaded through a different plate, and the total height was around 30mm (from memory.)

    Wish I had used Lewis Plates on my timber frame first floor; would have been sooo much better than the polystyrene sheets with ali spreader plates, which I would not recommend whatsoever!
    • CommentAuthorMike1
    • CommentTimeNov 3rd 2019
     
    <blockquote><cite>Posted By: Rex</cite>I cannot find the link but they also do (or may be did) a system where the small diameter UFH piping is threaded through a different plate, and the total height was around 30mm (from memory.)</blockquote>
    Sounds like their Max4 system: https://reppel.nl/en/composite-steel-floor-decking-systems/max4 ?
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