Toilet under the stairs: can you fit one, and what does it need?
Yes, you can usually put a toilet under the stairs, and in many London terraces it is the only place a downstairs WC will fit. Whether it works comes down to four things: a way to get waste to the drain (by gravity if the soil pipe is close, or with a macerator if it is not), extract ventilation, a hand basin in the room or just outside it, and enough height at the front of the pan to stand up. The room must also be separated from the kitchen by a door. A plumber can tell you on one visit which of these are easy in your house and which will drive the cost of the job.
Loyal Plumbers · Updated
Discuss your plumbing workThe quick checks before you get anyone round
You can rule the idea in or out yourself with a tape measure and a look at the outside of the house. None of these checks is final, but they tell you whether a survey is worth booking.
- Headroom: measure the height under the stairs where you would stand in front of the pan, not just at the tall end of the cupboard
- Length: the pan and the space in front of it both need to fit into the full-height part, with the low end used for the cistern or a shelf
- Soil pipe: find the nearest soil stack or manhole outside; a toilet close to it and able to fall towards it can drain by gravity
- Outside wall: an under-stairs space against an outside wall makes ducting an extractor fan much simpler
- What is already in there: gas and electricity meters, the consumer unit and the water stopcock often live under the stairs and may need moving or boxing in
Drainage: gravity toilet or macerator?
A normal toilet empties through a 100 mm or 110 mm pipe that has to fall steadily to the soil stack or drain. Under-stairs WCs are often in the middle of the house, so the question is whether that pipe can run under the floor, or along a wall, without needing to go uphill. On a suspended timber floor it frequently can. On a solid concrete floor the pipe may have to be cut into the slab, which adds work but is often still the better long-term answer.
Where gravity is not possible, a macerator unit grinds the waste and pumps it through small-bore pipe to the stack. It is a legitimate solution, but Approved Document H only allows a macerator WC where the home also has access to a toilet that drains by gravity, so it suits a second WC but should not be your only one. Our guide to macerator toilet pros and cons covers the noise, power and blockage trade-offs in more detail.
| Gravity toilet | Macerator toilet | |
|---|---|---|
| Works when | The pan can fall to the stack or a drain connection | The stack is too far away or too high to reach by gravity |
| Building work | Can mean lifting floorboards or cutting a solid floor for the pipe | Small-bore pipe runs in walls and floor voids more easily |
| Day-to-day use | Silent, no power needed, tolerant of use | Pump runs after each flush, needs electricity, strict about what goes down it |
| Allowed as the only WC? | Yes | No, a gravity WC must also be available in the home |
What the Building Regulations expect
Adding a toilet involves new drainage and ventilation, so in England it normally counts as building work that should be approved by building control or signed off through a registered installer scheme. It is worth sorting out before work starts, because buyers' solicitors ask for the paperwork when you sell.
The main technical points come from three Approved Documents. Approved Document G says a room containing a toilet must be separated by a door from anywhere food is prepared, including the kitchen, and that a hand basin should be in the WC or in a room you pass through to reach it, as long as that room is not the kitchen. In a house, a WC with its own basin inside can open off a kitchen without a separate lobby. Approved Document F covers ventilation: an under-stairs WC rarely has a window, so it normally needs a mechanical extract fan ducted to outside. Approved Document H covers how the new pipe joins the drainage, including the macerator rule above.
If the stair is part of a protected escape route, for example in a house with three or more storeys, building control will also want to know that the new room does not weaken it. Your building control officer or approved inspector can confirm what applies to your layout.
In a flat, a new toilet usually connects into a shared soil stack and may alter the structure. Check the lease and get the freeholder's consent before planning the pipe route; our guide to leasehold plumbing alterations explains what normally needs permission.
Making a small space work
Most under-stairs cloakrooms are laid out along the length of the stairs, with the toilet facing the door or the side wall where the ceiling is highest. A few choices make a real difference to how usable the room feels.
- Short-projection pans and compact close-coupled toilets save space in front of the pan
- A concealed cistern can sit under the lowest part of the stairs, as long as there is an access panel for repairs
- A corner or slimline basin with a small tap keeps the basin requirement from eating the floor space
- An outward-opening or sliding door avoids the door swinging into the pan
- Plan the extractor fan's position and duct route before the ceiling is boarded
What a plumber will look at on the survey
A useful survey should end with a clear answer on drainage route, ventilation route and what needs moving, not just a price. Expect the plumber to lift a floorboard or check the floor construction, locate the soil stack and nearest manhole, look at the water supply for the cistern and basin, and note any meters or cables that are in the way. If the drainage route is uncertain, a short CCTV drain survey from the nearest manhole can confirm depth and direction before anything is cut.
Ask each installer the same questions so quotes can be compared: gravity or macerator, how the fan will be vented, who deals with building control, what happens to anything already under the stairs, and whether electrical work for the fan or macerator is included. Our plumbing quote checklist has a longer list.
Getting a downstairs toilet planned and fitted
Loyal Plumbers fits new toilets, basins and pipework across London and everywhere inside the M25, from under-stairs cloakrooms to full bathrooms. If you are weighing up whether the space under your stairs will take a WC, call us or send an enquiry with a photo of the space, its rough measurements and where your soil pipe is, and we will tell you what the survey needs to check.
Common questions
- Do I need building regulations approval for a toilet under the stairs?
- Usually yes. A new WC involves drainage and ventilation work, which in England is normally building work that needs approval or sign-off through a registered installer. Check with your local building control before you start.
- Can a downstairs toilet open straight off the kitchen?
- In a house, a WC can open off a kitchen if there is a door and the hand basin is inside the WC. What is not allowed is having the only basin in the kitchen, or no door between the toilet and the food preparation area.
- Does an under-stairs toilet need a window?
- No. It needs ventilation, which without an openable window normally means a mechanical extract fan ducted to outside.
- Can I use a macerator for an under-stairs toilet?
- Yes, as long as the home also has a toilet that drains by gravity. A macerator is useful when the soil stack is too far away or too high, but it is noisier and needs power.
- How much headroom does an under-stairs toilet need?
- The practical test is whether an adult can stand comfortably in front of the pan and sit down without hitting the underside of the stairs. Measure at the spot where you would stand, not at the tallest point of the cupboard.
Sources and further reading
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