You fit a wall-hung toilet in five stages: get the waste into the right position and at the right height, anchor the support frame dead level to floor and wall, connect the water and pressure test it, close up the duct wall, and only then hang the pan. That order is not optional. Everything you get wrong before the wall goes up costs you a bolster and lump hammer later. Reckon on a long weekend, and on 350 to 900 euros of materials if you do it yourself.
Hello DIYer,
A wall-hung toilet is one of the nicest jobs you can do in a house. You gain space, you can mop underneath it, and that ugly waste pipe in the corner disappears behind a clean flat wall.
But it is also the job where I see most people come unstuck. Not because it is difficult. Because they work in the wrong order.
The classic: the frame is in, the wall is closed, it has been tiled, and then the pan turns up. And then it turns out the seat height is wrong, or the toilet sits 4 centimetres too far to the left, or the flush pipe just will not line up. At that point you are ripping out a day’s work.
So I am not just going to talk you through the steps. Mostly I am going to give you the sizes and the decisions you have to make up front, because that is where the whole difference sits.
What exactly you are buying: the parts
A quick glossary, because in the merchants four terms get used interchangeably.
| Part | What it is | What to watch |
|---|---|---|
| Support frame (carrier frame) | The steel frame that carries the pan | Height, load rating, height-adjustable |
| Concealed cistern | The cistern inside the frame | Depth 8, 9 or 12 cm |
| Flush plate (push plate) | The panel in the wall | This is also your access panel |
| Wall-hung pan | The toilet itself | Projection, rimless or with a rim |
| Seat | Separate or supplied with the pan | Soft-close, quick release |
Frame and cistern you almost always buy as one set. The flush plate is usually separate, and it has to suit the make and model of the cistern. Mixing and matching does not work here: a plate from brand A will not fit a cistern from brand B.
Important: buy a frame and cistern from a brand with proper spares availability. That thing sits behind your wall for twenty years. A flush valve or a float valve will be due for replacement in ten years, and at that point you want to be able to simply order the part. This is not the place to save fifty euros.
The sizes that decide everything
Take your time here. This is 80 per cent of the job.
Frame height: 112 or 82 centimetres
The standard height of a support frame is 112 centimetres. That is the usual size if you are building a normal duct wall up to ceiling height or to roughly a metre.
There are also low frames of 82 centimetres. You use those if there is a window above the toilet position, or if you want a low duct wall with a shelf on top to put things on. Downside: the flush plate ends up lower, and you have less margin in the height adjustment.
Seat height: standard or comfort height
You decide this before you fix the frame.
- Standard: 40 to 43 centimetres from the finished floor to the top of the seat.
- Comfort height: 46 to 50 centimetres.
Comfort height is pleasant for tall people and for anybody who struggles to stand up. For small children it is the opposite, their feet dangle.
Work backwards: the pan plus seat is roughly 4 to 5 centimetres thick above the fixing points. And do not forget the floor build-up. If you still have 4 centimetres of tiles plus adhesive to come, your whole height shifts with it.
Rule of thumb: measure from the finished floor, so including the tiles that are not down yet. This is the most common mistake in the entire job.
Decent frames adjust in height by roughly 8 centimetres during installation. Use that margin, but write down on a scrap of paper what you set it to before you start screwing anything down.
Space around the pan
- Legroom in front of the pan: at least about 50 centimetres, preferably 60.
- Clear space left and right of the pan: at least 20 centimetres, measured from the centre line of the pan.
- Minimum room width: roughly 80 centimetres for comfortable use. Tighter is possible, but then your knees are against the door.
- Projection of the pan: 48 to 57 centimetres, depending on the model. Short-projection pans exist and are handy in a narrow cloakroom.
Depth of the duct wall
This is the question everybody asks: how much space do I lose?
Reckon on:
| Part | Thickness |
|---|---|
| Concealed cistern | 8, 9 or 12 cm |
| Frame and setting-out clearance | 1 to 2 cm |
| Boarding (gypsum fibreboard or tile backer) | 1 to 2.5 cm |
| Tile adhesive and tiles | 1 to 1.5 cm |
| Total | 11 to 18 cm |
With a slim 8 centimetre cistern you end up around 11 to 12 centimetres of total wall thickness. With a standard 12 centimetre cistern you are heading for 16 to 18.
Tight on space? Then deliberately go for a slim cistern. It does not flush any worse, it is simply built wider and taller.
Fixing centres of the pan
The threaded studs the pan hangs on usually sit at 180 millimetre centres. That is the broad standard, which is why most pans fit most frames. There are also pans at 230 millimetres.
Check this before you buy. Frame and pan have to share the same fixing centres, otherwise it simply will not go together.
Load rating
A good support frame is rated for a load of roughly 400 kilograms. That is the usual standard for wall-hung pans and it is plenty, even with somebody standing on it to change a light bulb.
What actually matters: the frame has to be anchored properly, to the floor and to the wall. All the strength in the world is worthless if there are two undersized plugs in a plasterboard wall.
The waste: this is where most of it goes wrong
Before you buy anything, get down into the existing situation. What is there, and where?
Toilet waste is 110 millimetres as standard. You do not want to reduce that, not even over a short run.
Height of the waste
On a 112 centimetre frame, the connection for the waste bend generally sits around 20 to 23 centimetres above the structural floor. If your existing waste sits a lot higher or lower, you have to move it or bridge the difference with bends.
Measure the height of the centre of your existing waste pipe and lay it alongside the dimension sheet of the frame you have in mind. Costs ten minutes, saves you a day of misery.
Fall
This is the rule drainage stands or falls on. Literally.
- Minimum 5 millimetres per metre, so half a centimetre.
- In practice, work to 10 to 20 millimetres per metre.
Standard toilet waste size, minimum fall and maximum clip spacing. - Approved Document H covers drainage gradients in England and Wales, and the Dutch standard NEN 3215 works to a band of 5 to 20 millimetres per metre for horizontal collector runs.
Too little fall and the water stands still. But watch out: too much fall is wrong as well. On a steep run, the water disappears faster than the solids, the solids get left behind and that gives you blockages. More is not better here.
Clip a 110 pipe every 125 centimetres, so it cannot sag and lose its fall.
Air admittance
When a big slug of water goes down your waste, negative pressure builds up behind that plug of water. That negative pressure siphons the traps in your wastes dry, and then you smell the drains in your bathroom.
That is why the system needs air let into it. In most houses that happens through the soil vent pipe that goes up through the roof. If you connect your toilet a long way from the stack, or run a new branch, you may need an air admittance valve (a one-way valve that only lets air in). You fit that at the highest point of the branch, and it has to stay accessible.
If your toilet smells after the work is done, this is almost always the cause. Not the pan.
Access for rodding
Build a rodding eye into the run, somewhere that stays accessible. If the pipe blocks in fifteen years, you do not want to smash up your new tiled wall to reach it. This costs you twenty euros now and saves you a small fortune later.
The wall: will it take it?
A wall-hung toilet full of water plus an adult sitting on it is easily 150 kilograms of leverage on your wall. Look carefully at what you are fixing it to.
Solid wall (blockwork, concrete, brick). Fine. Anchor it with the wall fixings supplied with the frame, into the right plugs. With aerated or lightweight blocks: genuinely use the supplied or specified fixings, not whatever plugs are in the drawer.
Stud partition or lightweight blocks. Here the frame anchors mainly to the floor. Good support frames are self-supporting and strictly speaking only need fixing at floor level. The wall fixing is then just stabilisation. Do not guess: read the installation instructions for your frame.
Timber joisted floor. Extra care needed. The floor fixing has to land in a joist or in extra timber or steel noggins you have put in, not just in the floor decking. A frame screwed into 18 millimetres of chipboard will work loose eventually.
Underfloor heating in the screed? Find out where the pipes run with a thermal camera or a pipe detector before you drill. A drilled underfloor heating pipe is one of the most expensive mistakes you can make in a bathroom.
Step by step: setting the frame
1. Isolate and clear the room. Turn the water off at the stopcock or at the service valve for the toilet. Old pan out, old waste taped over so it does not smell and nothing falls in.
2. Mark out on the floor and the wall. Centre line of the toilet, the outside face of your duct wall, and the position of the flush plate. Mark the finished floor height as well, so including tiles. Fifteen minutes’ work, and you have the whole job in front of you.
3. Set the frame to height. Wind the adjustable feet out until you have the seat height you want. Most frames have a scale or a marking for the standard height. Do not forget you are measuring from the finished floor.
4. Get the frame level. In two directions: side to side and front to back. Do this properly, because a frame that is half a degree out of plumb shows up later in a crooked pan and in a flush plate that does not sit flat in the tile.
5. Anchor it. Floor bolts first, then the wall fixings. Tighten diagonally, then check level again. Frames like to shift while you are tightening up.
6. Push against it. Seriously. If the frame moves even a millimetre, it is not right. Loosen off, reset, fix again.
Connecting the waste
7. Fit the waste bend to the frame. Usually with a push-fit rubber coupling or with solvent weld, depending on your situation. A push-fit coupling is more forgiving for the DIYer because you can still rotate it.
8. Connect to the existing pipe with the right fall. Cut the pipe square, deburr the inside edge with a knife, and use lubricant on rubber seals. Solvent welding only happens on clean, dry, lightly abraded parts.
9. Test the waste before you close anything up. Pour a bucket of water into the waste bend and watch whether it goes away and whether anything is dripping. Do this with a torch in your hand, along every single joint.
Connecting the water
10. Run a supply to the water connection on the cistern, usually half an inch. Choose a route you can reach through the flush plate opening if it ever goes wrong.
11. Fit an isolation valve (a service valve or a built-in stop valve) in the supply. This is not optional. Without one you have to drain the whole house for every small job.
12. Flush the pipe through before you connect it to the cistern. Building debris in a float valve is a dripping toilet for the rest of its life.
13. Put the supply under pressure and leave it for at least a few hours. With the wall still open. Come back and wipe every joint with a dry piece of kitchen roll. This is the single most important test of the whole job, and the most skipped.
Building the duct wall
14. Fill the void with mineral wool. Two reasons: sound and condensation. A concealed cistern full of cold water in a warm room can sweat, and the fill helps against that. And it makes an audible difference to the flush noise, which matters most if there is a bedroom on the other side.
Is the toilet against a wall with a living room or bedroom behind it? Then think about an acoustic isolation kit: rubber strips and sleeves that decouple the frame and the pipe penetrations from the wall. They exist for all the common brands. Without decoupling, your frame passes the flush vibration straight into the masonry, and then the whole upstairs hears somebody going to the loo.
15. Board the frame using the template supplied. Almost every frame comes with a card template showing exactly where the cut-outs go for the threaded studs, the waste, the flush pipe and the flush plate. Use it.
Choice of board:
- Moisture-resistant plasterboard (green): cheap, fine in a cloakroom with no shower.
- Gypsum fibreboard: stronger and heavier, a better base for tiles.
- XPS tile backer board with a cement coating: the best choice in a wet room, waterproof and light.
If you are tiling: two layers of board with staggered joints is considerably stiffer than one layer. In a bathroom that gets wet, that is money well spent.
16. Tank it if somebody showers in the same room. Sealing tape in the corners, sealing collars around the penetrations, and a liquid membrane across the whole board. Do this before tiling, because afterwards you cannot.
17. Tile or plaster the wall. Make sure the tile falls neatly around the opening for the flush plate. Set this out before you start tiling, so you do not end up with a wafer-thin sliver of tile next to the plate.
Hanging the pan and finishing off
18. Cut the flush pipe and the pan connector to length. Slide the pipes into the pan, hold the pan in position, mark, and only then cut. Cut square, deburr, and lightly grease the seals with soft soap or a silicone-free lubricant.
19. Fit the acoustic isolation kit under the pan (the rubber mat or the washers). This stops porcelain rubbing straight onto tile, which gives you hairline cracks in the long run.
20. Hang the pan and tighten evenly. Both nuts alternately, a turn at a time. Tighten until it is firm, then stop. Too tight is porcelain cracking.
21. Seal the joint between pan and tile. Sanitary silicone, thin bead. Leave the bottom of the joint open over roughly a centimetre, or run a thin bead. That way you can see a leak instead of it running invisibly into your wall for years.
22. Fit the flush plate. The plate frame first, following the instructions, then the plate onto it.
23. Set the flush volume. Inside the cistern you can set both the full flush and the reduced flush. From the factory that is often 6 and 3 litres. In many cases you can drop back to 4.5 or 4 litres full and 2.5 or 3 litres reduced without it flushing any worse. On a rimless pan that usually works fine, on an older model with a long waste run less so. Try it and wind it back if it does not clear properly.
Quick sum: with an average household and roughly five flushes per person per day, a litre and a half off every full flush already saves a few thousand litres of water a year. Not an earth-shattering amount on your bill, but it is free.
What you have to sort out now for later
A concealed toilet is beautiful until something breaks. These three things decide whether that is fifteen minutes or a demolition day.
1. The flush plate is your access panel. Behind that plate sit the flush valve, the float valve and usually the isolation valve. So never tile over it, and never silicone it shut. It has to come off without tools or with one screw.
2. Keep the isolation valve reachable. Behind the plate: fine. Somewhere else in the wall: fit an access panel or make sure it stays outside the wall.
3. Take photos before you close up. Of everything. Pipes, waste, fixings, height dimensions with a tape measure in shot. Put them in a folder. In eight years you will want to know exactly where that water pipe runs before you drill for a towel hook. This is the best fifteen minutes you will invest in the whole job.
Common mistakes
- Measuring from the structural floor instead of the finished floor. Your seat height then does not match your tile thickness.
- Choosing the pan only after tiling. You need to know the fixing centres and the projection before you set the frame.
- Not fitting an isolation valve.
- Skipping the pressure test and then closing up the wall.
- Giving it too much fall on the assumption that steeper is better.
- Ignoring air admittance and then complaining about drain smells.
- Anchoring the frame to the wall only and skipping the floor fixing.
- Drilling into a floor with underfloor heating without looking first.
- Not filling the void, after which the flush is audible through the whole house.
- Siliconing or tiling over the flush plate.
- Overtightening the nuts and cracking the pan.
- Leaving no rodding access in the pipe run.
What does it cost?
| Item | Realistic range |
|---|---|
| Support frame with concealed cistern | 150 to 450 euros |
| Wall-hung pan | 100 to 400 euros |
| Soft-close seat | 30 to 150 euros |
| Flush plate | 40 to 200 euros |
| Boarding, wool and fixings | 60 to 150 euros |
| Pipe, fittings, isolation valve, sealant | 40 to 100 euros |
| Tiles and tile adhesive | 25 to 90 euros per m² |
| DIY, materials total | 350 to 900 euros |
| Contracted out to a plumber, installation only | 400 to 900 euros labour |
| Complete toilet replacement including tiling | 1,500 to 3,500 euros |
Guide prices, excluding any rerouting of the drainage or a new soil stack. That item can add up sharply if the toilet is moving to a different position in the house.
Where to economise and where not to: economise on the flush plate (you can always upgrade that later) and on the tiles. Do not economise on the frame, the cistern and the isolation valve. That is exactly the kit that disappears behind the wall.
When do you call a plumber?
Doing it yourself is perfectly achievable if you are reasonably handy. But call somebody if:
- You have to reroute the drainage over more than a metre or through a floor.
- A new soil stack or ventilation arrangement is needed.
- The wall is load-bearing and you have to go through it.
- You live in a flat with a shared soil stack. The freeholder or management company usually has rules about it, and work on shared pipework is almost never something you are allowed to do yourself.
- There is lead or galvanised pipework you have to alter.
Always ask whether the work on the water supply is being done in line with the Water Supply (Water Fittings) Regulations using approved fittings, and ask for a photo of the pipework before the wall closes up.
A word about ventilation
While you are at it: look at the extraction. For sanitary accommodation, the Dutch building regulations work to an air change capacity of at least 7 dm³/s, roughly 25 cubic metres an hour. If the room doubles as a bathroom, the heavier requirement of 14 dm³/s applies. In England and Wales, Approved Document F works to 6 litres per second of intermittent extract for a toilet and 15 litres per second for a bathroom, which lands in the same range. Source: IPLO
In practice: a toilet should have a fan or grille that extracts directly to the outside, and air has to be able to get in. A gap of roughly 1 centimetre under the door, or a grille in the door. Without make-up air the best fan in the world extracts nothing, and all you are doing is moving air around.
A refit is the moment to get that right in one go, because you are in the wall anyway.
Frequently asked questions
How high should a wall-hung toilet be?
The standard seat height is 40 to 43 centimetres, measured from the finished floor to the top of the seat. Comfort height is 46 to 50 centimetres and is pleasant for tall people or anybody who struggles to stand up. Always measure from the floor as it will finally be, so including tiles and adhesive. Good support frames still adjust in height by roughly 8 centimetres during installation.
How deep does the duct wall for a concealed cistern get?
Reckon on 11 to 18 centimetres in total. That is the cistern (8, 9 or 12 centimetres), the frame’s setting-out clearance, boarding of 1 to 2.5 centimetres and tiles with adhesive at roughly 1 to 1.5 centimetres. If space is tight, go for a slim 8 centimetre cistern. It does not flush any worse, it is simply built wider and taller.
Can a wall-hung toilet go on any wall?
No, but nearly. On solid brickwork or blockwork it always works, provided you use the specified fixings. On a stud partition or lightweight blocks you use a self-supporting frame that is anchored mainly to the floor. If the floor is timber joisted, make sure the fixing lands in a joist or in extra noggins, not just in the decking. A good frame carries roughly 400 kilograms, but that only holds with proper anchoring.
How much fall does a toilet waste need?
Minimum 5 millimetres per metre, in practice you work to 10 to 20 millimetres per metre. Approved Document H covers drainage gradients here, and the Dutch NEN 3215 works to a band of 5 to 20 millimetres per metre for horizontal collector runs. Too little fall gives you standing water, but too much is wrong as well: the water then runs away faster than the solids, and that is precisely what causes blockages. Clip a 110 millimetre pipe every 125 centimetres.
Can I still get to the concealed cistern after tiling?
Yes, through the flush plate. That is not just a push button but also your access panel: behind it sit the flush valve, the float valve and usually the isolation valve. So never tile over it and never silicone it in place. If a component sits outside that reach, for example a stop valve further along in the wall, fit a separate access panel for it.
Why does my toilet smell of drains after the work?
Almost always because of air admittance. When a lot of water goes down the pipe at once, negative pressure builds up behind the plug of water and that siphons the traps on your wastes dry. Without a water seal, drain air comes straight into the room. Check that your branch is connected to a properly vented system, or fit an air admittance valve at the highest point of the branch. Keep it accessible.
How much water does a wall-hung toilet use?
A concealed cistern often comes set to 6 litres for the full flush and 3 litres for the reduced flush. Inside the cistern you can set both volumes, and on modern rimless pans dropping the full flush back to roughly 4 to 4.5 litres usually works fine. Try it: if it does not clear properly, you simply wind it back. A litre and a half off every full flush already saves a family thousands of litres a year.
How long does it take to fit a wall-hung toilet yourself?
Reckon on a long weekend for an average job, spread over several days because you have to let things dry and test in between. Roughly: a day for stripping out, waste and frame, a day for the water connection, testing and closing up the wall, and a day for tiling plus final fitting. If the drainage has to be rerouted, add a day.
Are you taking on the whole toilet or the bathroom? Then there is more to it than just the pan: the duct wall, the waterproofing and the tiling decide whether it still looks sharp in ten years. In Koning van je Woning I show you how to build up walls, tank them properly and tile them the way it should be done, with the details that trip people up in practice.
Do yourself a favour. Before you close that wall: put the supply under pressure, go away for a few hours, and come back with a dry piece of kitchen roll along every joint. That fifteen minutes could save you a whole bathroom.
Regards from Fred Schouten, handyman and DIYer through and through
PS: take photos of your open wall. With a tape measure in shot. Your future self, wanting to hang a hook in eight years’ time, will thank you.