February 8, 20233 yr 5 minutes ago, mgo said: such a lot of info here, my wonder is do you always need to break up the old concrete floor? If you have enough headroom, what could be the disavantage to just add a layer of PIR insulation on top of the old concrete, add UFH and level off with screed. Leaving out DPM all together when the original cement floor is not damp. I am in the same situation (assuming no insulation / DPM currently under current old cement floor), and am looking into installing it this way, rather than opening up and excavating all excisting flooring. Steamy Tea will tell you you need a lot more insulation under ufh than you think or it will waste heat and you will freeze. I used 100mm Kingspan Kooltherm K103 and it seems to have worked ok, but I really wish we could have had more. PS don't believe the builder who tells you heat rises so you don't need much, it's not true, the concrete sucks the heat away.
February 8, 20233 yr Could use 120mm of PiR and then float a Fermacell routed solution over the top if you’re using a hard surface finish like tiles. Other option is 22mm chipboard but make sure the UFH track layer is perfectly flat. Liquid screed would need 50mm min so you’ll need 170-180mm overall build up depth available which may be a challenge at external doorways
February 8, 20233 yr 4 hours ago, mgo said: break up the old concrete floor Always add a dpm. I have kept old floors many times, but have always de-stressed them. If they are not cracked, then crack them. That probably isn't necessary when pir is going on top but I would have to think on this. Why break out and dispose of concrete then buy more in? Existing door lintel heights could be important.
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