Installing a Geberit WC Frame with Boxing-In

The difference from a basic frame installation is that the installer does not leave you with a bare metal frame. You get a finished false wall with a flat surface, an opening for the flush plate and the studs for the pan sticking out. The job usually involves:

• Setting out the position and height of the frame from the finished floor level and the centre line of the pan
• Fixing the frame to the floor and wall and setting it level and plumb
• Connecting the pan connector bend to the drain and the cold water supply to the isolating valve inside the cistern
• Pressure testing the supply and checking the waste connection for leaks
• Fitting the protective covers on the flush plate opening, the pan connector and the threaded studs
• Building the false wall from aerated concrete blocks or plasterboard on a metal stud frame
• Where agreed, a shelf above the frame or a false wall right up to the ceiling

The item does not normally include the waterproofing membrane, tiling, fitting the pan or the flush plate. These steps come after boxing-in, although the same tiler often does them. Before you order, be clear about where the installer's work ends.

The single most important figure is the finished floor height. The frame is set from that, not from the current concrete. If nobody yet knows whether there will be a new screed, underfloor heating or just tiles on the existing base, the installer has to guess, and a wrong guess cannot be put right later without breaking out the wall. Mark a "finished floor" line on the wall or give the exact floor build-up, and you avoid a lot of trouble.

Pipework and space

• A waste pipe of adequate diameter needs to reach the WC position. In a block of flats it usually comes from the shared soil stack. The connection must fall towards the drain.
• The cold water supply should be brought roughly to where the cistern will be. The installer will sort out the exact position, but the pipe should not end on the other side of the room.
• The wall behind the frame must be solid. Kombifix is fixed mainly to the masonry. Duofix carries the load through its legs into the floor, but it still needs a firm fixing at the top.
• If you want a socket for a shower toilet seat or lighting near the WC, an electrician must run the cable before the boxing-in goes up.

Decisions to make beforehand

The installer needs to know which pan and flush plate you will have, what size of tile and how you want the tiles set out. The depth of the pan decides how far from the wall you will sit. The tile format decides whether the flush plate opening lands in the middle of a tile or on a grout line. Anyone who leaves this until tiling often finds the flush plate sits a few millimetres off a joint, and it looks untidy.

Flats and building rules

If the work touches the soil stack or shared pipework, contact the building management or owners' association beforehand. The water often has to be shut off for the whole riser, or a new branch fitting has to be agreed. For larger alterations, such as removing a bathroom pod or changing the room layout, check the local building regulations with your local building authority. Do not assume that every change is just routine maintenance.

Setting out and fixing the frame

The installer first marks the centre line of the WC, the finished floor height and the position of the waste. The frame legs are extended to suit the floor build-up, the frame is offered up to the wall and levelled in both directions with a spirit level. The seat height follows from the height of the fixing studs. The manufacturer prints marks on the frame to set this. A usual seat height is roughly 400 to 460 mm above the finished floor. Taller people or older users may prefer the upper end.

Then the frame is fixed. The legs are screwed to the floor and the top brackets to the wall. In older prefabricated walls, hollow clay blocks or aerated concrete you need suitable wall plugs. If the wall is not solid, the top fixing is made through an extra support rail or through the masonry box-in itself.

Connecting water and waste

The pan connector bend is joined to the drain pipe, with a reducer or extension where needed. The bend has to sit so that, after tiling, it projects the right length for the pan. The water supply is taken to the isolating valve in the cistern, which you can later reach through the flush plate opening. Then comes the pressure test. The pipe is pressurised and the installer watches whether the pressure drops or anything drips. It is worth seeing the test yourself. Once the frame is boxed in, a leak is hard to find.

Boxing-in

In the masonry version, aerated concrete blocks are laid around the frame, usually 50 to 100 mm thick, bonded with thin-bed adhesive. The blocks are cut around the bend, the supply and the flush plate cover and fit tightly against the frame. In the dry version, a frame of metal studs and tracks or the manufacturer's own system rails is built around the WC frame. This is then clad with moisture-resistant plasterboard, for a WC normally in two layers so the wall does not flex.

Finally the surface is checked for flatness with a long straightedge. It must be flat enough for tile adhesive, and the covers over the openings must stay in place. They are trimmed only after tiling, not before.

How long it takes

Fitting and connecting the frame in a prepared bathroom usually takes a few hours. With boxing-in, a shelf and making good, it is typically one working day, more for a full-height false wall or a tricky connection. Adhesive on aerated concrete usually needs at least until the next day before further work. The waterproofing is applied in two coats and each must dry according to the manufacturer before the tiler can start.

Aerated concrete

A block false wall is strong, heavy and good at deadening sound. Tiles stay put on it reliably and it does not flex, even under large-format tiles. It suits Kombifix especially well, as that frame is designed to be built in. The downsides are weight, more dust when cutting and longer drying. On older timber floors in houses, consider whether the floor can carry that load.

Plasterboard

A dry false wall is light, quick and needs no drying time. It is common with Duofix and on longer false walls where the WC, basin and a concealed shower valve all sit in one line. To stop tiles cracking, the stud frame must be closely spaced, the board moisture-resistant and, for a WC, preferably doubled. Mineral wool is often put in the cavities to cut flushing noise.

Half height or up to the ceiling

A false wall to the height of the frame with a horizontal shelf is practical: small items fit on the shelf and there is less tiling. But the shelf is one more edge that has to be tiled accurately and given a slight fall, so water does not sit on it. A full-height false wall looks cleaner and hides the soil stack better, but takes more material and time. In blocks of flats people often go full height precisely so the old pipework disappears.

The job goes quickly and without surprises in an empty, clean bathroom with a straight, solid wall, the waste in place and a known floor height. The installer then just sets out, fixes, connects, tests and boxes in.

These things make it longer and harder:

• The waste is in the wrong place and has to be extended or moved, or a channel cut in the floor
• The wall behind the WC is out of true, hollow or made of material that holds fixings poorly
• The frame goes in a corner where the boxing-in turns, or next to a window or door
• In a block of flats the box-in has to go around the soil stack and up to the ceiling
• You want a shelf, a recess or one false wall shared by the WC and basin
• In a house the floor is not yet finished and the height has to be worked out from the drawings
• The installer has to wait for other trades, such as an electrician for the shower toilet socket

The price list also has a separate item: Geberit frame installation (Duofix / Kombifix) without boxing-in. The frame, connections and test are the same. The difference is who builds the false wall and when. In practice:

• Without boxing-in the installer leaves a fixed and tested frame, and the false wall is built afterwards by a drylining fitter, a bricklayer or yourself
• With boxing-in you take over a finished surface ready for waterproofing and tiling, and one person is responsible for flatness and the correct thickness
• Without boxing-in, the installer must pass on exactly what wall thickness they allowed for, otherwise the stud and bend lengths may not work out
• With boxing-in the work spreads over two days because of drying, while fitting the frame alone often takes only part of a day
• Without boxing-in makes most sense when one crew is building a large plasterboard false wall for several fittings at once

If the bathroom has just the WC and one tiler for the whole room, the version with boxing-in is usually simpler. There is no coordination to manage and no argument about who caused an uneven surface.

• Wrong floor height. A frame set to the bare concrete ends up too low once screed and tiles are added. The WC sits low and the studs do not line up with the holes in the pan.
• Frame not level. You do not see it on the pan at first, but the flush plate is crooked and the tiler has to fiddle with cuts around it.
• Missing or rushed pressure test. A weeping joint shows up weeks later as a damp patch on the next wall or on the ceiling of the flat below.
• Box-in too thick. The pan studs and connector bend do not project far enough and the pan cannot be tightened properly.
• Thin board or wide stud spacing. The wall flexes when you sit down, grout around the pan cracks and the silicone peels away.
• Covers removed before tiling. Adhesive or debris falls into the cistern or bend, so the flush leaks or the waste blocks.
• Isolating valve forgotten. If the valve cannot be reached through the flush plate opening, there is nowhere to turn off the water just for the WC when the cistern needs repair.
• No waterproofing on the false wall. With a shower or bidet spray next to the WC, moisture gets into the plasterboard and the tiles come loose over time.

A handy DIYer with the right tools can do this job alone if the water and waste pipes are already in place and they can work accurately. If you need to touch the soil stack in a block of flats, agree it with the building management first. If you are not confident about the water connection, ask a plumber to do the pressure test. Read the manufacturer's fitting instructions carefully, because exact dimensions vary between models.

1. Turn off the main water supply and check that no water is flowing.
2. Mark the WC centre line on the wall and draw a line at finished floor height, including tiles and adhesive.
3. Extend the frame legs to suit the floor build-up and offer the frame up to the wall.
4. Level the frame both vertically and horizontally and check the height against the marks on the frame.
5. Drill the holes, fit suitable wall plugs and fix the legs firmly to the floor and the brackets to the wall.
6. Connect the pan connector bend to the drain with its seal and check the fall.
7. Connect the cold water supply to the isolating valve in the cistern as the instructions describe.
8. Pressurise the supply, leave it under pressure for the recommended time and check every joint.
9. Fill the cistern, do a test flush into the bend and watch for leaks at the waste.
10. Fit all protective covers on the flush plate opening, the bend and the threaded studs.
11. Build the false wall from aerated concrete blocks on adhesive, or from metal studs and two layers of moisture-resistant plasterboard.
12. Check flatness with a straightedge and confirm the studs project the right length for the tile thickness.
13. Let the adhesive dry as the manufacturer specifies, and only then move on to waterproofing and tiling.

Before tiling everything is still visible and can be fixed. Afterwards it cannot. When you take over the work, go through these points and do not hesitate to ask:

• The frame is solid and does not move or creak when you push it
• The height matches the marked finished floor and the agreed seat height
• The WC centre line is where you agreed, and the flush plate opening fits the tile layout
• The pressure test was done in front of you and no joint is dripping
• The isolating valve can be reached through the flush plate opening and turns off
• The connector bend and threaded studs project a length that suits the tile thickness
• All protective covers are in place and undamaged
• The false wall is flat without noticeable waves and, if plasterboard, does not flex
• The shelf or top edge is level, or has a slight fall away from the wall
• The area is cleaned up and you have the fitting instructions and frame model from the installer