Hi Guys (1st time post)

I am about to embark on a wet room project on our house,
The room is 1.8m x 1.6m, we are planning on using some sort of resin shower tray possibly 1200mm x 1200mm Marmox showerstone or Tuff 2, building up the surrounding floor with plywood to get the floor flush with the tray.
So my question is can we put UFH over the shower tray & the plywood, we are not using insulation boards or a foam shower tray due to possible point load issues with 2" mosaics,
The floor is floorboards on joists, so I plan to insulate between the joists with kingspan.

Any help & advice would be much appreciated.

Hi mate,

I would go for backer board in a wetroom and be sure to tank too.

My preference would be to use mat around the former instead of going over it. chancea re if your standing on that part of the floor you will have hot water running over you anyway.

Ive done wet areas using Impey formers and run Warmup and Devimat UFH over them with no problems. Helps dry the floor quicker too!

If you are using ply just be sure to put membrane over full area, former and floor. Tape all joins and internal corners etc.

I would fit the base to suit your finnished substrate height whenever possible

Thanks guys for your quick replys,
I realise it will all need tanking, we are planning on using the Marmox Backerboards on all the walls, & tanking the floor with some sort of membrane (thats probably another question)
We are wanting to put UFH on the tray as the tray is going to cover the bulk of the floor because we are not planning on putting in a shower screen.

If its your first time at this I'd use the Impey system. Its not cheap but it is pretty fool proof. Formers are 22mm thick and very easy to fit. Membrane comes on a roll, (5 or 10 square meters), and is self adhesive, it can also be tiled the same day as there is no drying time. Back up and tech help is pretty good too if its needed.

good advice from mouldy regarding contacting technical department.

You should be fine putting electric mat over former but I would check with the manufacturer of the membrane you intend to use just incase there could be any issues.

No issues with Impey, I can vouch for that having done it. Cant vouch for other systems but know it has been done

Thanks again for the replies,
Mouldy the Impey system is not going to be suitable for us, as you cant trim much of the trays (we have a corner to cut out 6"x4") the tuff2 says it can be trimmed & cut, not sure on the Marmox showerstone.
I'm not looking for an easy anyone can do diy kit, I am wanting the best possible job that will last pretty much forever, which I am more than capable of doing, once I iron out all the ins & outs if you get my gist.

Is this cutout some sort of boxing for services? You could probably get away this cutout on an Impey former, but I would contact them to ask.

Should add of course that the UFH will come under part P and will need signing off.

The cutout is going to be a boxed in frame for a wall hung toilet, The Impey website states trimming only 50mm,
I have an electrician down the road who will sort the part P

I have ordered the 1200x1200 Marmox showerstone as it has a centre drain & can be cut.
If I use the Devimat100 UFH over the showertray & plywood, do you recon the floor will be warm enough as there wont be the insulation values of using foam trays & boards?

I will be warm but, without insulation boards it will simply take longer to warm up and will cool down faster also.

Heat loss etc, will also depend on how well insulated the exsiting floor/ room is.

Do Devimat actualy say that the 150 should not be used with ply?

Different manuafacturer have different specs for for there products. I know that climatech sold at TG sell a 150w mat and also a 250w mat. They dont say that the either shoud't be used on timber substrates.

Generally the higher wattage is to be used for floors with less insulation and areas which could include conservatories example.

Also timber does offer insulation to an extent (thicker the better)

This is also why I cant stress enough that advice should be taken from manufacturers when unsure as products are made/ designed with different materials and with different capabilities so what works with one product may not work with a similar product manufactured somewhere else.

Ive used Devi over ply, concrete and Lux boards. However as tfs has said, if in doubt check with the manufacturer's tech departments.

Thanks again Guys for your help,
If needed I will speak to the manufactures tomorrow, they have all obviously been closed over the Christmas holidays, so I have been having to rely on what I can find on the web.

Originally Posted by Bucks.

Thanks again for the replies,

I'm not looking for an easy anyone can do diy kit, I am wanting the best possible job that will last pretty much forever, which I am more than capable of doing, once I iron out all the ins & outs if you get my gist.

If you are willing to go that far then just glass the whole floor area with fiberglass resin and cloth, go up the wall about 6 inchs and then after all the pinholes are sealed up you will have the bentley of waterproof floors and far cheaper than a precast pan and it will be monolithic (no seams) so you can be pretty confident that it will never leak.
Then you can put whatever you wish onto it.
Just build up the plywood heights first.
Recess the glass you cove up the wall so that you don't end up with a bulge where the wall material would ride over the cove.

Originally Posted by Alberta Stone

If you are willing to go that far then just glass the whole floor area with fiberglass resin and cloth, go up the wall about 6 inchs and then after all the pinholes are sealed up you will have the bentley of waterproof floors and far cheaper than a precast pan and it will be monolithic (no seams) so you can be pretty confident that it will never leak.
Then you can put whatever you wish onto it.
Just build up the plywood heights first.
Recess the glass you cove up the wall so that you don't end up with a bulge where the wall material would ride over the cove.

Well maybe thats a bit to much for me

Originally Posted by Bucks.

Well maybe thats a bit to much for me

LOL....probably cheaper however.....fiberglass is really not that hard to work with.

A possible issue you will encounter is the fact that all the liquid waterproofing materials I am familiar with do not adhere well to plastic. They dry and then can be pulled off with relative ease.
So, unless you can find a different waterproofing that will adhere to plastic, or maybe scarify the surface so that it will key itself onto the surface........

Originally Posted by tfs

Do Devimat actualy say that the 150 should not be used with ply?

Been looking into it a bit more (Things are a lot clearer now)
Devimat state
The devimat 100 Series is ideally suited to timber based floors.
The devimat 150 Series is ideally suited to heating tiled concrete floors.

Warmup state
When fitting the underfloor heater onto a timber subfloor, the floorboards or chipboard must be over-boarded with a suitable Warmup® Insulation Board or 18 mm WBP plywood. Existing floorboards must be fixed securely and, if necessary, pre-levelled with a latex/cement smoothing underlayment to give a flush fit for the WBP plywood or the Warmup® Insulation Board. Ply must be screwed at 200mm centres and installed as per BS 5385: Part 3 Clause 14.4.
Warmup® Insulation Board must be fixed with flexible tile adhesive. For best performance the board should also be secured with five screws and penny washers per board.
Warning: Fixing ply directly to the joists may not provide a sufficiently stable floor finish to accept tiles; fitting tongue and groove flooring and then over-boarding with ply or Warmup® Insulation Board is recommended.

Enermat State
The Enermat is primarily designed for installation on concrete floors. If layingEnermat on a wooden floor, all floors must be sheeted with Wedi board, Knauf Aquapanel or similar cement covered board which is compatible with heated floor systems or sheet the floor with 15mm WBP or Marine plywood, fix with screws at 200mm centres and then skim with 2-3mm of flexible tile adhesive and allow to dry, then proceed as installation for concrete base.

My Conclusioin
Pressure treated floor joists with Kingspan insulation between joists, area around shower tray T&G floorboards overboarded with 18mm WBP plywood, shower tray installed flush with plywood floor, walls boardered with Marmox 12.5mm tile backer boards, Tank Plywood floor inc showertray (I may also tank the walls in the main shower area, even though they should be waterproof if installed correctly) Then eventually 150w UFH (not 100% decided on what make yet)

Now for what to tank the floor with, I think I should maybe start another thread for this one.

THANKS for all your help & advise Guys its much appreciated