Electric underfloor heating over original flagstones

[hanpadge]

Hi there, I have a very small kitchen with a partitioned bathroom as a late 1800's stone addition to my 1850's Welsh stone cottage. The original flagstones are in good condition and run throughout the kitchen/bathroom but there is very little heating or space for rads etc so I want to lay electric heating mats over the flagstones and tile over it. I really want to protect the flagstones from any adhesives etc but will definitely need to level the floor at some stage of the process. I also have a very solid oak counter unit that I will have to work around and the large immovable furniture like cooker, bath, fridge etc that I won't lay underfloor heating under so will leave the flagstones uncovered under these.

I can't find a clear process or order that the different layers should go in for this situation. i.e. flagstone, insulation board, heat mats, tile. Is it possible to use sand or anything other than self leveling compound to even out the surface before putting down insulation boards or would it work to put insulation board straight onto the flagstones and then use the leveling compound on top of the heat mats to make the surface level? I think the heat mats might need to be even to avoid cold spots? I'm going round in circles so any insight would be very appreciated!

 

[Kearn]

It’s a really bad idea. Your flags will be allowing ground moisture to evaporate from their surface, and gaps.

They would have also been laid sensibly, often with ash, lime layers and the rest rather than just on the soil, so the will have some insulating properties under them.

Levelling them with compound is a terrible thing that will almost certainly cause irreversible damage to the floor. If you’re listed this will constitute criminal damage.

Sealing them will push ground moisture into the base of your walls and likely cause you damp issues there or an overload of moisture to evaporate, assuming the walls are correctly built up in lime and limewash. Anything modern will start to bubble and fail as the moisture pushes out.

Most of us dream of finding original floors under later modern crap that’s been laid over them.

Electric underfloor heating is also very inefficient, and expensive. And the heat doesn’t linger. It will also unlikely heat the room space, just takes the chill off the floor for bare feet.

Best think again really… IR electric wall heaters might be worth investigating if you genuinely can’t get wet heating onto the walls. They are slim and can be mounted up out of the way. And would be more financially and thermally efficient that the underfloor version