Insulation for underfloor heating.

[TheCaptain]

Hi all, been searching details on this site for a while but this is my first post.
I have concrete floors, some of which are at different levels because of the age of the house.
I wish to tile the kitchen floor and have electric underfloor heating. Area wise it's 3900mm x 5000mm. The original concrete floor has been brought up to near level with one ajoining room by way of 50mm insulation slab then 65mm screed. The chap in the tile shop says I'll still need insulation boards under the heating mat. Is this right or is insulation below the screed sufficient?
Many thanks, in advance, for everyone's time.

 

[Richard C]

The purpose of insulation boards directly under the heater mat is to reflect as much of the heat upwards rather than it being absorbed by the screed. If you don’t use backer boards, response & warm up time will be considerably increased. You should also lay a SLC over the heater element before tiling to protect it during tiling & if you want any chance of repairing it if it goes wrong; it will also give a flat tile base, important if your laying large format tiles. If tiling over screeds laid at different times or of different materials you may need an uncoupling membrane to avoid cracks developing where the two substrates meet. The screed must be fully dry – minimum 28 days but 1 day per mm thickness; the heating element should be commissioned before tiling. Use a flexible powder adhesive over the heater mat/SLC.

Personally I would question the wisdom of installing electric UFH in a kitchen; they tend to be warm enough places as it is. Neither are they very practical as a secondary heat source & can be expensive to run. I know several people that have UFH in their kitchen but never use it for these very reasons.

Read the tiling forum sticky & archive posts before you do any more work or buy materials, it may prevent you making catastrophic & potentially expensive mistakes. Use only quality trade tiling materials, own brand & DIY products are mostly crap.

 

[tpt]

the insulation board, as richard says will stop the UFH heating the 65mm of screed as well as your room. you can fit it without. it depends on your expectations for a UFH system. if its your primary heatsource then no question fit the boards (or reconsider as its not too great as a primary heatsource)

Again to echo richard, as a retailer that sells UFH i honestly would question its use. Tiles being cold is a myth, they merely reflect the ambient temperature and the temperature of the substrate, if your walking on your screed in bare feet now and dont think its cold then your tiles wont be - save yourself the cost and spend more on tiles and fitting instead.

Furthermore, in a kitchen i feel its least useful, bathrooms and living rooms then yes.

P.s. - none of this applies to wet piped UFH, which is the dogs danglies