Flagstones with UFH

mishkin

Hi all,

I'm renovating a small (75m²) cottage. I installed underfloor heating and the concrete slab wa poured over a year ago, so I'm guessing it's good and dry at this stage:)

I'd like to finish it with a flagstone floor, but my plumber is a little worried about the heat penetrating through the thickness of the flags...while he's installed plenty of ufh systems, he has no experience in dealing with flagstones so I think he's being overly cautious...but I'd really like some more opinions on this.

The first flagstones I'm looking at are limestone calibrated to 20mm from India

I also however have the option of locally sourced slate flags, but these vary in thickness from about 20mm to 40mm. These would be irregular shaped, but I could work them a little and the cottage is extremely 'rustic' anyway so I would be happy to use these.


The second option would be my preferred choice...I would love to get them locally, plus I like the random look of them...and also the price is definitely right! (tight budget!) but there are 2 issues I'm worried about with these flags:

1. If the plumber is worried about the 20mm...I'm afraid he'd freak completely if I mentioned the 40mm

2. If the flags are of varying thickness, I would have to 'grade' them to keep things levelish..but would this affect the heating (differing depths)?


So, I guess my question are:

Is there any limit on the thickness which can be used? (I realise responsiveness becomes an issue)

and

Is there any problem with flags of varying thickness?

Thanks

BryanF

UFH in a modern house should be on low & steady - constantly

I’m surprised you went with ufh in an old cottage assuming it will be a challenge to bring the Envelope fabric up to modern levels of insulation/ air-tightness/ damp proofing. I hope you have a load of insulation under and up the sides of the pipe work? Ideally exceeding current new build levels?

20mm flags I don’t see a problem, just a longer delay in getting heat from the underfloor system when compared to say a small tile. Remember to account for levelling compound thickness in your build-up calc.

Totally agree with your source local approach, but why not keep looking? I’d Forget the uneven flags unless you can find a local tradesman (& Pay him adequate) for dealing with that hassle, as it sounds like a pain in the ass to lay..

Calahonda52

Having an uneven floor is asking for trouble in my mind, first from a resale perspective and also a public liability perspective.
You have a Maria Bailey type claim and the assessor sees an uneven floor...
https://www.irishtimes.com/news/politics/maria-bailey-set-to-lose-fg-whip-over-swing-compensation-claim-1.3961865

mishkin

I’m surprised you went with ufh in an old cottage assuming it will be a challenge to bring the Envelope fabric up to modern levels of insulation/ air-tightness/ damp proofing. I hope you have a load of insulation under and up the sides of the pipe work? Ideally exceeding current new build levels?

Yes BryanF, the pipe are well insulated below and sides, the heating has been commissioned and is working great & the house seems to be holding the heat very well...I just don't want to go and ruin that now by installing the wrong type of flooring.

I’d Forget the uneven flags

I wouldn't say they're uneven exactly...the surface area is flat, it's just that they're of varying depths.

But thanks for the advice...it's much appreciated

mishkin

Calahonda52 wrote: »

Having an uneven floor is asking for trouble in my mind, first from a resale perspective and also a public liability perspective.
You have a Maria Bailey type claim and the assessor sees an uneven floor...
https://www.irishtimes.com/news/politics/maria-bailey-set-to-lose-fg-whip-over-swing-compensation-claim-1.3961865

I'm hoping I won't have too many of the Maria Bailey type calling to the door

I do understand your concern, but again..as in the reply above I'm hoping to achieve a very level surface area, without lips, obstructions etc