Subfloor advice for underfloor heating

[eddgrant]

Hi all,

We're replacing our kitchen, as part of the build we are taking up the existing broken floor (18mm floorboards) and replacing with a tiled underfloor heated floor. My builder has suggested creating the new subfloor using 18mm ply and doesn't want to use any insulated tile backer boards as it will increase the floor height too much.

I really want to use the tile backer boards as I want the UFH system to be as efficient as possible, so I spoke to a provider of the tile backer boards who believed that the 10mm boards should be sufficiently sturdy to use as a second layer on top of 12mm ply to create the subfloor. Does anyone have any information to confirm/ deny this? Would it be solid enough for the UFH kit and the tiles (600x600x10mm slate). Would there be any issues r.e. building regs doing this? Would I need to put in any extra noggins to stop the thin ply bending?

Would be grateful for viewpoints from anyone who has experience in this area as I'd like to avoid having a great big step up in to, and out from the Kitchen if possible.

Cheers,

Edd

 

[mointainwalker]

What is the construction of the existing floor ?

 

[eddgrant]

What is the construction of the existing floor ?

It's 18mm wooden floorboards over wooden joists (think they're spaced approx 400mm apart). The existing floorboards are badly damaged though so they're being removed entirely. The idea was to make a new ply subfloor on the joists.

 

[mointainwalker]

By far the best solution is to put 100/200 mm fibre-wool between the joists. This will not cost much more than those pathetic little boards you refer to and will give 15 times better insulation without raising floor-height at all.

Suggest 18mm ply for floor