A downstairs toilet — also known as a cloakroom, downstairs loo, or ground-floor WC — is one of the most practical additions to a UK family home. Properties without one are often marked down by estate agents; adding one can increase resale appeal and convenience in equal measure.
The cost for a basic downstairs toilet installed (WC, basin, tiling, plumbing, and electrical work) typically runs £2,000–£5,000. High-specification versions with bespoke joinery, designer sanitaryware, and premium tiling can reach £6,000–£9,000.
Full Cost Breakdown
| Element | Typical Cost |
|---|---|
| Structural partition or enclosure (if needed) | £400–£2,000 |
| Plumber — drainage connection, supply, soil stack work | £800–£2,000 |
| Electrician — extractor fan, lighting, Part P certification | £400–£800 |
| WC suite (close-coupled or wall-hung) | £150–£800 |
| Basin and vanity unit or pedestal | £100–£600 |
| Tiling — floor and half-wall | £400–£1,400 |
| Plastering and decoration | £200–£600 |
| Door (solid-core, with frame and ironmongery) | £200–£600 |
| Accessories (mirror, towel rail, soap dispenser) | £100–£400 |
| Building Regulations application fee | £200–£400 |
| Total — basic finish | £2,000–£5,000 |
| Total — mid to high specification | £5,000–£9,000 |
Prices are London and South East rates. Expect 10–20% less in the Midlands and North.
Where Can You Put a Downstairs Toilet?
The most common locations are:
- Under the stairs — ideal use of dead triangular space, and often close to the soil stack. See the detailed understairs guide for space requirements and geometry.
- Rear hallway or utility area — a more spacious option that often allows a more conventional rectangular layout.
- Converting a larder, coat cupboard, or small ground-floor room — works well in older terraces or Victorian houses with numerous small ground-floor rooms.
- Ground-floor extension — where there is no suitable internal space, a small rear or side-return extension can accommodate a cloakroom alongside other uses (e.g., a boot room).
Minimum Space Requirements
The absolute minimum floor area for a WC and basin is approximately 1.1 m × 1.5 m (1.65 m²), though this is very tight and offers little comfort. The recommended minimum per BS 8300 (accessibility) is closer to 900 mm × 1,700 mm for a standard close-coupled WC and compact basin.
A wall-hung WC with a concealed cistern built into a partition saves 150–200 mm of depth — this makes a significant difference in tight spaces and allows you to work with a shallower enclosure.
Headroom must be at least 1.9 m at the standing position (2.0 m preferred under Part K of the Building Regulations).
The Drainage Question
Getting the toilet waste out of the house efficiently is the central technical challenge of a ground-floor WC. Options:
Gravity Drainage (Preferred)
The WC pan connects to a 110 mm soil pipe that runs at a fall of 1:40 minimum (roughly 25 mm drop per metre of run) to the external soil stack. This is the most reliable option and the one Building Control inspectors prefer to see.
If the stack is on the rear wall and the proposed WC location is at the front of the house, a long gravity run may not achieve the required fall without going below floor level (which means breaking up the concrete ground floor slab). In these cases, the macerator route is often more practical.
Macerator Pump (Where Gravity Isn’t Feasible)
A macerator (brand names include Saniflo, SFA, and Sanimarin) sits behind or alongside the WC pan. It grinds waste and pumps it through a 22–32 mm discharge pipe to the soil stack — typically running horizontally at a gentle rise (1:100 maximum) for up to 12 m, or vertically for up to 4 m (always check manufacturer specifications).
Advantages: no major structural work; can be installed in almost any location.
Disadvantages: requires a dedicated 13A electrical connection; is audible during use (a short, low hum for 10–30 seconds); requires periodic maintenance (descaling and blade replacement every 5–10 years); should not be used with chemical drain cleaners; some manufacturers require a service contract for warranty purposes.
Macerator units cost £300–£800 for the unit itself; installation including electrical connection adds £400–£700.
Connecting to a Drain Rather Than a Stack
In some older properties without an external stack (e.g., houses where soil goes directly underground), a ground-floor WC can connect via a 100 mm pipe directly to the underground drain — but the pipe must still achieve the required fall, and an access rodding point must be provided near the connection.
Ventilation Requirements
An internal cloakroom with no openable window must have mechanical ventilation under Building Regulations Part F:
- Minimum extract rate: 6 litres/second continuous, or 15 l/s intermittent (triggered by the light switch, typically with a 15-minute overrun timer).
- Fan size: 100 mm diameter is standard.
- Duct run: maximum 6 m equivalent length (add 1.5 m per 90° bend).
- Duct must terminate on an external face of the building — not into a loft or void.
If the cloakroom has an openable window of adequate area (at least 1/20th of the floor area), natural ventilation is acceptable under Part F — but mechanical ventilation is still common practice for basements and internal rooms.
Building Regulations — What’s Notifiable?
Adding a downstairs toilet almost always requires Building Regulations approval. The notifiable elements include:
- Part H — drainage: connection to soil stack, pipe sizing, falls, and rodding access.
- Part F — ventilation: mechanical extract specification and duct route.
- Part P — electrical: extractor fan circuit and any new lighting circuit.
- Part A — structural: if walls are removed or trimmer joists disturbed for an understairs installation.
- Part M — access: where the property is a new build or undergoing a material change of use (less relevant for typical domestic conversions, but the minimum dimensions above are informed by this part).
You can apply via your local authority Building Control or use a registered approved inspector. Many plumbers and bathroom fitters will arrange a building notice on your behalf — confirm this before work starts. Failure to get sign-off can cause complications when selling.
Planning Permission
No planning permission is needed for an internal cloakroom conversion. If you’re building a small extension to accommodate the cloakroom, check whether it falls within Permitted Development rights (generally a rear extension up to 3 m depth for terraced or semi-detached, 4 m for detached, subject to height and other limits).
Sanitaryware Choices for Small Cloakrooms
Wall-hung WC — pan fixed to a steel frame (carrier frame) built into the partition; concealed cistern sits behind the wall. Adds a premium feel and saves floor depth; the carrier frame adds £200–£400 to the cost but saves space.
Close-coupled WC — cistern sits directly on the back of the pan. More affordable (£150–£500 for a decent suite); takes slightly more depth but is simpler to maintain.
Short-projection WC — a close-coupled WC with a reduced depth pan (sometimes called compact or short projection). Available from major manufacturers from around £200–£400; typically 48–52 cm projection versus a standard 65–70 cm — a significant saving in a tight space.
Cloakroom basin — compact basins (400–500 mm wide, 250–300 mm depth) are made specifically for cloakrooms. Corner basins can also work in very tight layouts.
How Long Does It Take?
A straightforward cloakroom installation (no structural alterations, gravity drainage close to the stack) typically takes 3–5 days across all trades. Add 1–2 days for any structural partition work, and allow a few extra days if the drainage route is complex or the floor needs breaking up.
Finding a Tradesperson
A downstairs toilet requires a plumber, an electrician, and usually a tiler. Some bathroom companies offer design-and-fit packages covering all trades. Always confirm:
- Who is responsible for the Building Regulations application.
- Whether the plumber is familiar with both gravity and macerator systems.
- That the electrician is Part P-registered.
Get at least three quotes and ask each tradesperson to walk through their proposed drainage route before committing — the drainage solution is the most variable cost element and will determine whether the project is straightforward or complex.
