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taking off concrete slab to retrofit piped UFH

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taking off concrete slab to retrofit piped UFH

Posted 12 Dec '19 03:21 PM

Hi there, so, this may be a bit of a crazy idea, but may bet not....: We have a house with a 100mm concrete slab with 665 HRC mesh 30mm from top and we would just love to put in some piped underfloor heating. The UFH system we have been offered so far would add 4cm height to the floor and the room height is only 230cm, so we are not keen to lose much of that height (I am tall, too). We have been thinking that maybe it is possible to take off a few centimeters from the concrete slab (3cm, down to the mesh??) and then put the UFH on top. That way we would only loose 1cm, which maybe we could even balance by putting flooring on top that is thinner than the current one. Does anyone know if this has been done/can be done? Would consent be required (I think if we keep some distance to the walls, it would not be considered an alteration to a supporting structure...)?
Any tips are welcome. Cheers!

RE: taking off concrete slab to retrofit piped UFH

Posted 14 Dec '19 02:29 PM

I would put your idea under mission impossible and you potentially compromise the structural integrity of your slab.

Have a look at this one.

RE: taking off concrete slab to retrofit piped UFH

Posted 14 Jan '20 01:55 PM

Thanks for your opinion and tip. Yes, I had a look at the variocomp before and we are still thinking about it. The other system we are considering, is a bit thicker 40mm, but already has an insulation layer built in, which the variocomp hasn't. If we would put some poly underneath the variocomp, we probably end up with the same height. Going without insulation would mean we loose less room height, but on the other hand we would loose more warmth into the ground...

RE: taking off concrete slab to retrofit piped UFH

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RE: taking off concrete slab to retrofit piped UFH

Posted 21 Jan '20 11:55 AM

I would say you would be undertaking a huge task to grind and cut away the top layer of the concrete slab, right down to the mesh. Really uncertain if this task would be achievable without compromising the slab strength.

I also think you shouldn't be too obsessed with losing 30 or 40mm in living space height. You'll find the cost to minimise this is not worth the effort. Also why the craze of wanting UFH? For a small area low ceiling height, a small conventional air source heatpump would easily fit the bill.

One problem I find with these retrofit UFH systems is the emphasis for insulation. Yes the heating response is quick but they lack thermal mass. With how NZ's electricity setup where you can have night rate at half the price of the day rate, the issue of storing heat applies. Our hydronic floor heating system we had standard pex piping on top of the mesh and the mesh sat on 50mm of EPS with no gaps between the sheets of EPS that you see with podded waffle slab insulation.

RE: taking off concrete slab to retrofit piped UFH

Posted 21 Feb '20 03:56 PM

Thanks to everyone who took the time to share their thoughts on this topic (not sure what to say about the completely unrelated posts....).
Just to let you know, we have decided to not touch the slab. We will use the 4cm UFH system which has some insulation built in. To minimize the loss of room height, we decided on flooring which is about 1-1.5cm thinner than our current carpet with underlay. The carpet is not too great for UFH anyway and we were never a big fan of it. So, with everything factored in our floor will rise about 2.5-3cms which we hope will not notice too much.
I find insulation (under the UFH) important to minimize heat loss into the ground. It is not so much the cost of electricity I am worried about but rather the electricity that is still consumed and needs to be generated, which eventually comes at some cost for the planet. Even though NZ´s power generation is comparably eco friendly, it still has some impact.

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