Tile over floorboards without raising height of floor

[Yellowduck]

I have come up with a possible solution as how to tile over bathroom floor without increasing height over adjoining hall way, and would appreciate your thoughts.

The total height of 10mm heat insulating board, UFH wire, and tile will be about 24mm....so

Remove all floorboards (19mm).

Remove 5 mm from top of each joist.

Fix 2 x 2 battens to either side of joists, 25mm below reduced height top of joists, and fix 25mm strips of marine ply in between each joist, and screw firmly to battens, so tops of marine ply strips level with tops of reduced height joists so you have a flat floor.

Fix heat insulation boards with flex adhesive to wooden floor. Fix UFH wire to HIB's and tile over with flex adhesive and 10-12mm tiles,

According to my calcs, the finished tile floor will be a similar height to the existing floorboards in the adjoining hallway.....

Could possibly get away without reducing height of joists, taking into account hall will have carpet and underlay.

Thoughts would be appreciated....

 

[AdamCH]

I think your floor won't be as strong as if the ply was on top of the joists. I'd just accept the raised floor height (fit a tapered threshold) or leave out the UFH.

 

[big-all]

yes its far more likely to crack as each joist will be unsupported by the joist each side
so instead off the flooring distributing the load to adjacent joist it will act more like a hinge

 

[Yellowduck]

Thanks....

OK point taken...... So how about I take 15mm off the top of each joist and board over completely with 25mm Marine ply, then 6 mm heat insulation boards, then UFH and tile.

This would give me about a 10mm overall increase in height (over the current vinyl floorcovering) which would be lost against the adjoining carpet and underlay.

I am talking about bathroom and shower rooms, so neither will have heavy traffic.

 

[big-all]

if theres no notches you might get away with it dependant on unsupported span and size
it may be easier to drop the floor joists 15mm

 

[AdamCH]

I think a more conventional approach, assuming the joists are good and the floor nice and rigid, would be use a good quality 18mm WBP Ply + lots of noggins to strengthen the joists and spread the load. You don't need 25mm Marine.

Going to be a hell of a faff to cut the joists down and they may end up too weak - you haven't said how deep they are, what the span is, whether they're notched/drilled for pipes.

If they're downstairs you may be able to drop them or support thinner joists with an extra sleeper wall.

You can get 6mm Marmox. It won't do much insulation wise (10mm min to insulate) but it will isolate the UFH from the ply. Since 6mm won't insulate much you may want an isolation mat (Ditra) rather than the 6mm boards.

Personally, I'd cope with a tapered threshold strip or drop the UFH.