Most Irish semis and terraces can fit an under-stairs toilet in a space about 80 cm wide and 140 cm deep, with standing height at the front. It needs no planning permission, but it needs a 6 l/s extractor fan with a 15-minute overrun. Build Me's fixed-price downstairs WC package costs €6,356 including VAT, and most jobs take about 2 weeks on site.
The space under your stairs probably holds coats, a hoover and a few things nobody has touched since you moved in. Turned into a cloakroom, it ends the queue for the upstairs bathroom and saves guests a trip through the house. There is one rule most people miss. In a windowless WC, the fan should keep running for a full 15 minutes after you leave. This guide covers space, rules, drainage, cost, timing and design ideas for a tiny room.
How Much Space Do You Need for a Toilet Under the Stairs?
Most Irish semi-detached and terraced homes have enough room under the stairs for a toilet and a small basin. The practical minimum is about 80 cm wide by 140 cm deep on the floor. That is a Build Me rule of thumb from fitting these rooms, not a legal figure. No Irish regulation sets a minimum size for a WC in an existing house.
Head height matters more than floor area. You need full standing height where you stand and wash your hands. Aim for about 1.8 to 2 m at the front of the room. The ceiling can drop to about 1.4 m at the back, because the cistern and the back of the pan sit low.
The trick is to face the toilet towards the high end. You sit under the sloping ceiling and stand up into the tallest part. The basin goes where your head clears it, usually beside the door.
| Measurement | Tight but workable | Comfortable |
|---|---|---|
| Floor width | 80 cm | 90 cm or more |
| Floor depth | 140 cm | 150 to 170 cm |
| Head height at the front | 1.8 m | 2 m |
| Head height at the back | 1.4 m | 1.5 m or more |
| Basin | Corner or 35 to 40 cm cloakroom basin | Slim 45 to 50 cm basin on a small vanity |
Source: Build Me rule of thumb for under-stairs WCs, October 2026. Measure inside the finished walls, not the bare cupboard.
What Building Regulations Apply to an Under-Stairs Toilet?
Planning rules rarely touch an under-stairs toilet, but the Building Regulations do. Four parts matter most. Each has a Technical Guidance Document (TGD) that shows one way to comply.
| Part | What it covers | What it means under the stairs |
|---|---|---|
| Part F, Ventilation | Extract rates and fan controls | 6 l/s fan with a 15-minute overrun, 10 mm door gap |
| Part G, Hygiene | Where WCs and basins go, flush volume | A door between WC and kitchen, basin in or next to the WC, 6-litre flush |
| Part H, Drainage | Pipe sizes, falls and pumps | 100 mm gravity pipe, or a pump to I.S. EN 12050 |
| Part B, Fire safety | Escape routes and fire doors | FD20 door only if the stairway is a protected route |
Sources: TGD F 2019, TGD G 2008, TGD H 2010 (2016 edition) and TGD B Volume 2 (2017), Department of Housing.
Ventilation and the Extractor Fan
Almost every under-stairs WC is windowless, so the fan does all the work. TGD F 2019 sets an intermittent extract rate of 6 litres per second for a WC with no bath or shower. That is a low bar. A standard 100 mm bathroom fan clears it easily.
The detail that catches people out is the overrun. Where a WC has no openable window and no background vent, TGD F asks for an automatic 15-minute overrun after switch-off. For a bathroom without a WC, a humidity sensor is an accepted alternative. For a toilet it is not, because the fan is there for smells, not steam.
In practice, the fan is wired to the light with an overrun timer, or to a motion sensor. TGD F also says any automatic control should have a manual override. It asks for the extract to sit as high as practical, no more than 400 mm below the ceiling. The duct should run to the outside by the shortest route, never into a ceiling void.
No. B&Q Ireland lists the Vent-Axia VASF100T timer fan at €104. It has a 5 to 30 minute overrun and extracts 75.6 m³/h, about 21 l/s. That is more than three times the TGD F rate for a WC.
Doors: Gaps, Kitchens and Fire Doors
The door is part of the ventilation design. TGD F 2019 says a 10 mm gap under internal doors lets air move between rooms. Without it, a fan in a sealed WC has nowhere to draw fresh air from, and it struggles.
TGD G 2008 says a room with a WC must be separated from a kitchen. In a house, one door is enough. TGD G also says the basin should be in, or next to, the room with the toilet.
Fire doors depend on the height of your house. Most two-storey homes have no floor more than 4.5 m above ground. TGD B Volume 2 (2017) needs no protected stairway in them. Some homes have a floor above 4.5 m, often three-storey homes or ones with an attic conversion. There, the stairway is usually a protected route. Doors onto it then need FD20 fire rating under TGD B Table B1. If that applies to you, the attic conversion regulations explain how the escape route works.
Electrics, Flush and Registration
The new light, fan and any macerator need a power supply. The Commission for Regulation of Utilities (CRU) says electrical work in your home should be done by a Registered Electrical Contractor. It says the contractor must give you a completion certificate, so ask for it and keep it with your house papers.
TGD G 2008 also caps the flush. Every WC should have a maximum flush of 6 litres or less. Nearly all new toilets, including dual-flush models, meet this. It only matters if someone suggests reusing an old high-volume cistern.
Plumbers do not need a statutory registration for this work in Ireland. RGI registration covers gas work only, so it does not apply to a toilet and basin. Pick a plumber you can check through recent jobs and reviews.
- Fan: at least 6 l/s, ducted outside, with a 15-minute overrun and a manual override.
- Door gap: about 10 mm under the WC door.
- Kitchen: a door between the WC and any kitchen.
- Basin: in or next to the WC.
- Flush: 6 litres or less.
- Fire door: FD20 if the stairway is a protected route.
- Electrics: Registered Electrical Contractor and a completion certificate.
Do You Need Planning Permission for an Under-Stairs Toilet?
No, in almost every case. Section 4(1)(h) of the Planning and Development Act 2000 exempts works that affect only the interior of a building. A toilet under the stairs is an internal alteration. A small fan outlet on an outside wall does not change the look of the house in a way that matters.
There are two exceptions. A protected structure needs permission for works that affect its character, inside as well as out. Many Victorian and Georgian homes in Dublin are on the Record of Protected Structures. Check your council's record first. The second is where a previous planning condition limits works to the house, which is rare for internal work.
Building Regulations apply even when planning does not. Small internal works like this rarely need a Commencement Notice. If the job alters the stair structure or fire separation, ask your council's building control section before you start.
Soil Pipe or Macerator: Which Works Under Your Stairs?
Drainage decides the cost and the mess more than anything else. You have two choices: a gravity connection to the soil pipe, or a macerator that pumps the waste. Ask your installer to check gravity first. It is simpler and needs no power.
Gravity Soil Pipe
A gravity WC drains through a 100 mm pipe, the minimum TGD H sets for a toilet. TGD H gives a fall of 9 to 90 mm per metre for a common WC branch pipe. So the pipe must drop steadily all the way from the pan to the drain or stack.
On the ground floor, TGD H lets a WC pipe run straight to a drain if the drop is 1.5 m or less. That often makes life easier under the stairs. The hard part is the route. In many Dublin semis the soil stack is at the back and the stairs are at the front.
Reaching the drain can mean cutting a channel in the concrete floor and digging down to the drain run. That adds a few days, dust and floor repairs, but it gives you a normal toilet with nothing to maintain.
Macerator (Saniflo-Type Pump)
A macerator sits behind or beside the toilet. It grinds the waste and pumps it through a small pipe to the nearest soil stack. Saniflo's Irish agent lists the SaniPlus UP at €825 including VAT. It pumps up to 5 m up and 100 m across through pipe as small as 22 mm.
The pipe can run inside a stud wall or behind skirting, so there is usually no floor to break. TGD H accepts pumped drainage where gravity drainage is impracticable. It asks for units to I.S. EN 12050 and an alarm to warn you of a fault.
The trade-offs are real. A macerator needs a fused power supply and some noise when it runs. Only toilet paper can go down it, so wipes and sanitary products will block it. Plan for descaling and, eventually, a replacement pump.
| Factor | Gravity soil pipe | Macerator |
|---|---|---|
| Pipe size | 100 mm | 22 to 40 mm |
| Floor work | Often a channel cut in the floor | Usually none |
| Power needed | No | Yes, a fused supply |
| Noise | Normal flush | Pump hum after each flush |
| What can be flushed | Normal use | Toilet paper only |
| Unit price | No pump to buy | €825 (SaniPlus UP); B&Q Ireland lists the Sanislim at €798 |
Sources: TGD H 2010 (2016 edition); Saniflo Sales Ireland and B&Q Ireland product pages, prices checked 26 October 2026, incl. VAT, supply only.
- No floor to break up
- Toilet can sit far from the stack
- Faster, cleaner install
- Needs power and a fault alarm
- Toilet paper only
- Pump wears out over time
How Much Does an Under-Stairs Toilet Cost in Ireland?
Build Me's fixed-price downstairs WC package is €6,356 including VAT, for a toilet and basin in a new cloakroom. It sits alongside our fixed-price bathroom packages, which start at €9,307 for a full bathroom. We check the drainage route at the site visit before we confirm the price.
Drainage is the biggest variable. A gravity connection next to the stack is the simplest case. A long run, a cut floor or a macerator adds work or parts. A SaniPlus UP pump alone is €825 including VAT from Saniflo's Irish agent.
Finishes are the second variable. A wall-hung toilet with a concealed cistern, full-height tiles and a brass tap cost more than a close-coupled pan and painted walls. The good news is the small size. A cloakroom needs only a few square metres of tile. So a better tile costs less here than anywhere else.
If you want a shower as well, the job becomes a small shower room. Our bathroom calculator puts a small ensuite in Dublin at €5,000 to €10,000. It also needs more space and stronger extraction than a WC. A shower rarely fits under a stair, so most people fit one elsewhere as an ensuite bathroom.
| Item | Price incl. VAT | Source |
|---|---|---|
| Downstairs WC package (toilet and basin) | €6,356 | Build Me fixed price, 2026 |
| Small ensuite with a shower, Dublin | €5,000 to €10,000 | Build Me bathroom calculator, 2026 |
| Essential bathroom package | €9,307 | Build Me fixed price, 2026 |
| SaniPlus UP macerator, supply only | €825 | Saniflo Sales Ireland, October 2026 |
| Sanislim macerator, supply only | €798 list (on offer at €405, out of stock) | B&Q Ireland, October 2026 |
| Vent-Axia timer fan, supply only | €104 | B&Q Ireland, October 2026 |
Prices checked 26 October 2026. Retail prices are supply only and do not include fitting.
How Long Does It Take to Fit a Toilet Under the Stairs?
Most under-stairs toilets take about 2 weeks on site, by Build Me's estimate. That fits the 1 to 4 week range for bathroom work in general. A macerator job can be a few days quicker, because nobody needs to break the floor. A gravity job with a long floor channel takes longer.
The sequence is the same as any bathroom. The trades follow each other, and some days nobody is on site while plaster or adhesive dries. You can use the rest of the house as normal. Expect dust on the first few days, and plan where the coats and hoover will live from now on.
- Before workSurvey the space and the drainage route.Measure the width, depth and head height, find the nearest soil stack and decide between gravity drainage and a macerator.
- Days 1 to 2Clear the cupboard and form the room.Remove shelving and old fittings, build any new stud walls and frame the door opening, and cut the floor if a gravity pipe needs a channel.
- Days 2 to 4Fit the first-fix plumbing and electrics.Lay the waste pipe, bring a cold supply to the toilet and basin, and run cables for the light, the fan and any macerator.
- Days 4 to 6Board, plaster and waterproof the room.Line the walls and sloping ceiling, plaster or skim them, and waterproof the floor and splash areas before any tiling.
- Days 6 to 8Tile the floor and walls.Lay the floor tiles and any wall tiles, then let the adhesive and grout cure before fixtures go on.
- Days 8 to 10Fit the second fix and decorate.Connect the toilet, basin and tap, fit the fan with its overrun timer and the lights, hang the door with its 10 mm gap, then paint and hand over.
The electrician should give you a completion certificate at the end. Run the fan, test the flush and check the door clears the toilet before you sign off.
What Are the Best Under-Stairs Toilet Design Ideas?
In a room this small, every centimetre counts. A toilet that sticks out 5 cm too far can stop the door closing. These ideas come up again and again in good Irish cloakrooms. Many of the same tricks work in any small bathroom.
Wall-Hung or Short-Projection Toilet
A wall-hung toilet is the favourite for under-stairs rooms. The cistern hides in a slim frame against the back wall, and the pan floats off the floor. You see more floor, so the room feels bigger, and cleaning is easier. Short-projection pans stick out less. That can decide whether the door closes or not.
The frame needs a boxed-in wall about the height of the cistern. Under a stair, that is usually the low back wall, which suits it well. Keep the flush plate where you can reach it under the slope.
If the back wall cannot take a frame, a back-to-wall toilet is the next best choice. The cistern hides in a slim unit behind the pan, and it needs a little more depth.
| Toilet type | Floor space | Cistern | Best for |
|---|---|---|---|
| Wall-hung | Least, floor stays clear | Hidden in a wall frame | Most under-stairs rooms |
| Back-to-wall | A little more depth | Hidden in a slim unit | Walls that cannot take a frame |
| Close-coupled | Most depth | On show, on the pan | Deeper rooms and tight budgets |
| Basin on the cistern | Saves a separate basin | Basin built into the lid | The tightest spaces |
Build Me comparison of toilet types for under-stairs rooms, October 2026.
Compact, Corner or Combined Basin
Basin size changes the whole layout. B&Q Ireland's basin buying guide says basins range from 160 mm to 500 mm deep. A cloakroom basin will probably only be used for washing hands, so it can be small and shallow.
A corner basin frees floor width where the room is narrow. A basin on a slim floating vanity hides the waste pipe and gives you a drawer for spare toilet rolls. In the tightest rooms, a toilet with a basin built into the cistern lid saves a whole fitting. The rinse water fills the cistern for the next flush.
Fit the tap on the wall if you can. A wall tap lets you use an even shallower basin, and it keeps the counter clear for soap.
Pocket, Sliding or Outward-Opening Door
A normal door that swings into a tiny WC eats the space you need to stand. There are three better options. A pocket door slides into the wall, so it takes no floor space at all. It needs a stud wall beside the opening, with no pipes or switches in it.
A surface sliding door runs on a track outside the room. It is simpler to fit but needs clear wall beside the opening in the hall. An outward-opening door is the cheapest fix, as long as it does not block the hall or the bottom step when open.
Keep the 10 mm gap at the bottom for air. If your stairway is a protected route, the door must be FD20 rated. Fire-rated pocket doors are harder to find.
Bold Colour, Wallpaper and Panelling
A downstairs WC is the one room where you can be brave. Visits are short, so dark paint and loud wallpaper feel fun rather than heavy. Deep green, navy, aubergine and terracotta all suit the cosy shape of an under-stairs room.
Wallpaper on the sloping ceiling turns the awkward angle into a feature. Tongue-and-groove panelling to about 1 m protects the walls where people brush past. A single wall of patterned or zellige-style tile behind the toilet gives impact for a small tile budget.
Keep the floor practical. Porcelain tile is the easiest to keep clean around a toilet. Use a moisture-resistant paint or a vinyl wallpaper, because a WC basin still splashes.
Sensor Lighting and Clever Storage
Without a window, good light makes the room. A motion sensor light switches on as you open the door and suits children and guests. Pair a downlight with a small wall light or a backlit mirror, so the room does not feel like a cupboard.
Link the fan to the light with its overrun timer, and it will run itself. A quiet fan matters, because the WC is often near the living room or kitchen.
For storage, use the low space at the back of the slope. A shallow shelf over the cistern box holds spare rolls and soap. A recessed niche between studs adds storage without taking depth. Hooks on the back of the door replace a towel rail.
Does a Toilet Under the Stairs Add Value?
Usually yes, but treat any percentage with care. UK research by the estate agent comparison site GetAgent, reported in August 2021, put the gain at about 5% of a home's value. We could not find an equivalent Irish study, so use that only as a rough guide.
In practice, a downstairs WC is one of the features buyers of Irish family homes look for. It matters most in three and four-bed semis, where one upstairs bathroom serves the whole family. It is also a strong point for older buyers, because nobody has to climb the stairs during the day.
By comparison, a full shower room on the ground floor of a small house can feel like lost space to some buyers. A simple WC under the stairs avoids that, because it uses space that was only ever a cupboard. If you plan to stay a few years, you get the daily benefit as well as the selling point. If you are selling very soon, a kitchen or main bathroom refresh may give a quicker return.
Send us a photo and the measurements of the space under your stairs. We will check the drainage route and confirm whether it fits our €6,356 downstairs WC package.
FAQ
What is the minimum size for a toilet under the stairs?
About 80 cm wide by 140 cm deep, with around 1.8 to 2 m of head height at the front. That is a Build Me rule of thumb, not a legal minimum.
Does an under-stairs toilet need an extractor fan?
Yes, if it has no window. TGD F 2019 sets a 6 l/s extract rate for a WC. Without an openable window or background vent, the fan needs an automatic 15-minute overrun.
Do I need planning permission for a downstairs toilet?
No, in nearly all cases, because internal works are exempt under section 4(1)(h) of the Planning and Development Act 2000. A protected structure is the main exception.
Can I put a toilet under the stairs without a soil pipe nearby?
Yes, with a macerator. It pumps waste through a small pipe to the nearest soil stack. The SaniPlus UP can pump up to 5 m up and 100 m across.
How much does an under-stairs toilet cost in Ireland?
Build Me's fixed-price downstairs WC package is €6,356 including VAT. A macerator pump, if your drainage needs one, costs about €800 to supply.
Can a downstairs toilet open into the kitchen?
Not without a door. TGD G 2008 says a room with a WC must be separated from a kitchen, and in a house a door is enough.
How long does it take to fit a toilet under the stairs?
About 2 weeks on site in most homes, by Build Me's estimate. A macerator job can be a few days quicker because the floor stays intact.
Next Steps
- This week: empty the cupboard and measure the width, depth and head height at the front and back.
- This week: find your soil stack and note how far it is from the stairs.
- Within 2 weeks: check whether your home is a protected structure, and whether the stairway is a protected route.
- Within 2 weeks: book a site visit, so the drainage route can be checked and the price confirmed.
- Before work starts: choose the toilet, basin, tiles and door, so nothing holds up the second fix.
Useful Tools and Resources
- Build Me bathroom renovation calculator: prices a refresh, a full bathroom or a small ensuite in Dublin or the rest of Ireland.
- TGD F 2019, Ventilation: the extract rates and overrun rules for a windowless WC.
- TGD G 2008, Hygiene: where a WC and basin can go, and the 6-litre flush limit.
- CRU, Electrical works in your home: why you need a Registered Electrical Contractor and a completion certificate.
- Planning and Development Act 2000, section 4: the exemption for works that affect only the interior.
Sources
- Build Me, fixed-price bathroom and downstairs WC packages and bathroom renovation calculator (2026)
- Department of Housing, Technical Guidance Document F, Ventilation (2019), paragraphs 1.2.1.2, 1.2.1.3, 1.2.4.3 and Table 3 (accessed 26 October 2026)
- Department of Housing, Technical Guidance Document G, Hygiene (2008), paragraphs 2.4, 2.5 and 2.7 (accessed 26 October 2026)
- Department of Housing, Technical Guidance Document H, Drainage and Waste Water Disposal (2010, 2016 edition), paragraphs 1.2.2.5, 1.3.5 and Table 3 (accessed 26 October 2026)
- Department of Housing, Technical Guidance Document B, Fire Safety, Volume 2, Dwelling Houses (2017), paragraphs 1.3.2 to 1.3.4 and Table B1, copy hosted by Mayo County Council (accessed 26 October 2026)
- Irish Statute Book, Planning and Development Act 2000, section 4(1)(h) (accessed 26 October 2026)
- Commission for Regulation of Utilities, Electrical works in your home (accessed 26 October 2026)
- Saniflo Sales Ireland, SaniPlus UP product page (price checked 26 October 2026)
- B&Q Ireland, Saniflo Sanislim macerator 400W (price checked 26 October 2026)
- B&Q Ireland, Vent-Axia VASF100T bathroom extractor fan 100 mm (price checked 26 October 2026)
- B&Q Ireland, Basin buying guide (accessed 26 October 2026)
- Property Reporter, Which home renovations will add the most value to your home when selling? GetAgent research (6 August 2021)
