Tiling on floorboards

[Yellowduck]

Hi,

We are having an extention built and can set the concrete floor to suit the wet underfloor heating and tile levels, to suit the flooring in the rest of the bungalow.

However, we would also like to tile the existing bathroom and shower room floors which are currently floor boards. We accept that to use wet underfloor heating would make the finished height (with tiles and backing board) about 40mm above the hall floor which would be ridiculous.

So we are thinking of removing the existing floor boards (19mm) and replacing with 19mm marine ply screwed securely to the joists. We would then use heat insulating backing boards fixed down to marine ply with adhesive. Then electric underfloor heating kit wire on the backing boards, finished off by tiling with flex adhesive and grout.

This would result in the finished tile floor about 25mm above the floorboards in the adjoining hall which is still a pain.

Can anyone advise a method that would minimise the height differential between the two floors, other than raising all the remaining floors in the bungalow!

If we did away with the heat insulation backing boards and put the wires directly on the marine Ply (this would keep the increase in height to about 18mm) would this be sufficient insulation under the wires, and would flexible adhesive and flexible grout cope with the limited movement of the marine ply.

Thanks

 

[tpt]

The insulation boards are always required - especially over wood which is an insulator anyway. best bet for me would be to take up the floorboards, insulate underneath with celotex\kingspan, then fit the ply, then fit the electric UFH direct to the ply.

one thing you dont say is what your expectation of the UFH is, i.e. if its the primary heat source or the secondary. Electric for primary can be a bit touch and go, depending on the room size\windows etc.

 

[Yellowduck]

Thanks.

The UFH will be secondary to radiators and just to warm the tiles on a cold night!

I was thinking of using marmox insulation boards on top of the ply and then the element and tiles. Do you think if I were to put the celotex between the joists under the 19 mm WBF this would be enough insulation so I could tile straight over the element onto the WBF?

On another point, where the tiles end up higher than the floorboards in the hall, in the past where I have had this, I have used flooring compound to make a gradual slope from the higher floor to the lower one over the width of the door, and once the underlay and carpet is down, it is barely noticeable.

If anyone has a better suggestion I would be grateful!

Cheers

 

[tpt]

You'll get far better insulation from 50mm celotex underneath than an insulation board, so yes if your taking the floor up anyway its a much better option.

As a secondary heat source electric UFH will be fine. If you use noggins etc to make sure the ply has no movement, then no need to use a backerboard at all, just a good quality flexi addy so your levels should be fine.

 

[AdamCH]

I'm no expert on UFH but I don't think you want to be laying it directly on Ply - it will expand and contract, especially with UFH. You haven't said what power the UFH is or what tiles you'll be using or whether you need to waterproof the floor.

Your Marmox plan is probably the best (it's waterproof, insulating and good to tile onto) - use 6mm instead of 10mm if your not worried about insulation or have put Celotex under the floor.

You might be able to use Ditra/Durabase over the ply - save you a couple of mm.

If you end up with a small step then a timber threshold strip will probably look ok.

 

[tpt]

Hi AdamCh - as long as you dont exceed 150w/m2 (fine for a secondary heat source) then you can go direct onto ply. Marmox\no more ply over the ply is always going to be better, but as height is the main issue it could be removed providing the ply is fixed at 200mm centres

Ditra\Durabase doesnt do the same job as a backer board so dont swap out for that.

 

[AdamCH]

Hi Tpt

Agree that Ditra won't insulate but I'd have thought it would help isolate the tiles from the expanding/contracting ply - it's job being to isolate tiles from lateral movement.

 

[tpt]

ah yep, in that case we agree sorry. That said i'd be surprised if theres enough lateral to worry about