UFH on suspended floors - questions!

Discussion in 'Builders' Talk' started by Riri87, Mar 19, 2021.

  1. Riri87

    Riri87 New Member

    Hi all,

    in the process of planning wet UFH on the ground floor of our house. We have suspended joists (5x2).

    Looking at options, im leaning towards running the pipes on 30-50mm of pir (battened) and then running 20-25mm of dry pack 8:1 sand cement over the pipes before boarding with chipboard and floor covering.

    My question is whether i should run a dmp over the dry pack between the chipboard board to stop any moisture from the sand getting to the board. Any thoughts?

    Not sure how 8:1 sets, should i board straight away or leave it a couple of days?

    any other considerations? Ive checked the dead loading and we have enough sleeper walls for that to not be an issue.

    is this the best way considering costs and thermal performance?

  2. Scooterdemon

    Scooterdemon New Member

    Normal would be to use spreader plates or preformed insulation, definitely not cement.
    rogerk101 and Riri87 like this.
  3. Riri87

    Riri87 New Member

    Thanks Scooterdemon - a preformed insulation board was my initial thought but people have said that the thermal performance would be better with a dry pack.

    i was looking at cement boards and preformed insualtion instead of chipboard and screed but the costs become prohibitive.
  4. Scooterdemon

    Scooterdemon New Member

    What size is the area? Have you considered aluminium spreader plates they are far less expensive.
  5. Riri87

    Riri87 New Member

    Its around 35sm across 2 rooms (kitchen and dining) and a hall way.

    I have looked at alum plates - again the issue for me is performance. This will be the only heat source in the rooms so want to maximise output.

    would you suggest alum offer the right balance of performance and cost? Labour time would be pretty much equal across all methods.

  6. rogerk101

    rogerk101 Screwfix Select

    Aluminium spreader plates will maximize heat output and respond far quicker than any type of screed.
    Riri87 likes this.
  7. Riri87

    Riri87 New Member


  8. FlyByNight

    FlyByNight Screwfix Select

    My own lounge, 8m x 5m has UFH on a suspended floor using speader plates. It works very well. Use te preformed boards, with an extra layer of Celotex or similar below.
    Riri87 likes this.
  9. I-Man

    I-Man Screwfix Select

    I have aluminium spreader plates, with 100mm celotex underneath, 18mm caberboard on top, followed by LVT. Gets nice and hot pretty quickly, but cooling down is also the same.
    I was always under the impression a screed would hold heat longer after the heating is off?
  10. Riri87

    Riri87 New Member

    Do you hear the aluminium at all during heating/cooling?
  11. FlyByNight

    FlyByNight Screwfix Select

    My spreader plates are steel, but no noise from them

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