So thinking of putting some electric u/floor heat in the downstairs loo which will have procelain tiles.

Do people recommend I remove the old floor boards and install some other board onto the joists ?

I need to stick to about 40mm total makeup including a 10mm tile.

(Thinking of using thermosphere - can you integrate it into heatmiser ?)

Edited 15 hours ago15 hr by Spinny

I would keep the boards if they are solid and level, and put a tile backer board over them rather than taking them up. That saves height and gives the tiles a stable base to work from. With 40mm total and a 10mm tile, you have about 30mm left for the backer, mat and adhesive, so a thin backer board makes more sense than a thick one. Screw it down well, stagger the joints, and check the floor does not bounce before you tile. For the Heatmiser question, I would check it with the mat maker, as some mats need their own sensor and controller setup.

Thanks, stevenlee - wow you are far away - do you live in CA ?

However I didn't make it clear - the 40mm is from top of joist - so it would include 21mm floorboards leaving around 19mm...

Top of Joist

Floorboard 21mm

backer board ?

Flexible Tile adhesive to stick down matt 2.5mm

Matt with electric cable 5.5mm

Flexible Tile adhesive 3mm

Porcelain Tile 10mm

Total 42mm + backerboard... so too high

I don't have any insulation between the joists at the moment.