Loft En-Suite Cost Calculator
A loft en-suite is priced by where the waste goes, not by the tiles. If the soil stack is reachable it is an ordinary small bathroom. If it is not, the cost roughly doubles before you have chosen a single fitting.
Open the calculator →Price your loft en-suite in 30 seconds
4 steps. Waste route, room size, spec and region.
How this calculator works
Every loft en-suite question comes back to the soil stack. A gravity connection to a stack that already runs past the room is the cheap answer at £350–£900. A new external stack is £900–£2,500 and needs the wall, the scaffold and often the neighbour considered.
A macerator looks like the easy way out at £450–£1,200. It is also audible through the floor of the room below, and it is a pump — it will fail eventually, and it will fail in a room with a WC in it. Treat it as the last resort the plumbing trade treats it as.
On ventilation: this is the one room in the house where poor extraction has somewhere cold to condense. Ducted to outside, not into the roof void — a fan that discharges into the loft will wet the insulation and you will find out two winters later.
Loft en-suite cost line by line (2026)
| Line item | Typical 2026 cost | Notes |
|---|---|---|
| Stud walls, door and structure | £600–£1,400 | Depends on room size and layout |
| Soil connection to existing stack | £350–£900 | Cheapest option by a wide margin |
| New external soil stack | £900–£2,500 | Where no stack is reachable |
| Macerator / pumped waste | £450–£1,200 | Last resort — adds a fault point |
| Hot and cold first fix | £550–£1,200 | From the cylinder or combi |
| Suite, shower and tiling | £1,800–£4,500 | Where spec moves the price |
| Extraction ducted to outside | £180–£450 | Never into the roof void |
Figures match our loft en-suite planning guide. Bathroom electrics are notifiable under Part P — ask who is certifying.
Loft en-suite calculator FAQs
Only if gravity will not reach a soil stack. Where the stack runs past the loft, a normal connection is cheaper, quieter and has nothing to break. A macerator is a pump in a bathroom — it works, but it is the answer of last resort, not the default.
On a combi or a mains-pressure unvented cylinder, usually yes. On an old gravity-fed system with the tank in the loft you are now level with or above it, and you will need a pump or a system change — price that before you commit to the room.
It is covered by the loft conversion application, but the electrics are separately notifiable under Part P. Ask who is certifying them and get the certificate before the final invoice.
Two to three square metres is enough for a shower, WC and basin if the head height is there. Head height is the real constraint in a loft — you need to stand up at the shower and at the basin, not just in the middle of the room.
Related cost guides
- Loft en-suite guide — soil stack, falls and ventilation
- Bathroom plumbing costs — first and second fix
- Loft conversion costs — every type priced
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