The short answer
Fitting out a basement, the work after the waterproof shell is complete, typically costs around £600–£1,500 per square metre, depending on the use of the room. A plain habitable room with insulation, lining, flooring, lighting, heating and decoration sits at the lower end. Adding a bathroom or kitchen raises the rate sharply, because the basement is below the main drain and waste has to be lifted by a pumped system, plus tiling, plumbing and fitted units. Lighting designed for a windowless space, ventilation to meet building regulations, and good-quality finishes all add. The fit-out is the part of a basement budget you have most control over, since the structural and waterproofing costs are largely fixed but the finish is a choice.
The fit-out is the stage where a waterproof concrete shell becomes a usable room, and the part of a basement budget you can flex the most. The sections below set out per-square-metre fit-out costs and what moves them.
Typical fit-out rates
- Plain habitable room~£600–£1,000/m²
- Higher-spec living space~£1,000–£1,500/m²
- With bathroom / kitchenAdds pumped waste + fittings
- LightingDesigned for windowless space
- ExcludesShell, waterproofing, structure
What the fit-out covers
The fit-out is everything that turns the finished, waterproofed shell into a habitable room. That includes insulation and lining over the waterproofing system, a finished floor, electrics and a lighting scheme suited to a space with little or no natural light, heating, ventilation to meet building regulations, plastering and decoration. Because the waterproofing must remain unbroken, the lining is fixed in a way that does not penetrate it, which is a particular feature of basement fit-out. For a plain room used as a study, gym or den, this is the bulk of the work, and the per-square-metre rate stays at the lower end of the range.
| Fit-out level | Typical rate | What it includes |
|---|---|---|
| Plain habitable room | £600–£1,000/m² | Line, floor, light, heat, decorate |
| Higher-spec living space | £1,000–£1,500/m² | Better finishes, joinery, lighting |
| Adding a bathroom | Extra | Pumped waste, tiling, fittings |
| Adding a kitchen | Extra | Pumped waste, units, services |
Indicative UK figures for guidance only. Rates exclude the structural shell and waterproofing.
Why wet rooms cost more
The single biggest fit-out variable is whether you add a bathroom or kitchen. Because a basement sits below the level of the main sewer, waste cannot simply drain away by gravity, so it has to be lifted by a pumped drainage system (a sump and pump or a packaged pumped unit) up to the drain above. That pump, its electrics and resilience add cost, on top of the tiling, plumbing, sanitaryware or kitchen units themselves. A basement with a shower room or kitchenette therefore has a noticeably higher fit-out rate than a plain dry room, which is worth deciding early because it affects both the budget and the services that must be designed in.
Where you can control the cost
The fit-out is the part of a basement budget you can most easily flex, because the structural shell and waterproofing are largely fixed but the finish is a series of choices. Keeping the basement as a plain habitable room, with simple flooring, standard lighting and no wet rooms, holds the per-square-metre rate down. Choosing higher-end finishes, bespoke joinery, a designed lighting scheme, a bathroom and a kitchenette, pushes it up. Unlike the dig and the waterproofing, where economising is unwise, the fit-out is a legitimate place to match the spend to the room's purpose and your budget.
It still pays to plan the fit-out alongside the shell rather than after it. Lighting, heating, ventilation and any pumped waste all need to be designed in before the linings go up, and the means of escape and ventilation must satisfy building control regardless of finish. A basement fitted out thoughtfully, with services planned early and the waterproofing protected, gives a comfortable, dry room at a per-square-metre rate you can largely control, which is a welcome contrast to the more fixed costs earlier in the project.
Frequently asked questions
Does fit-out cost include the waterproofing?
No. The fit-out is the finishing stage after the waterproof shell is complete, covering lining, flooring, lighting, heating, ventilation and decoration. The waterproofing system and the structural shell are separate, largely fixed costs earlier in the project.
Why does a basement bathroom or kitchen cost extra?
Because the basement sits below the main sewer, waste has to be lifted by a pumped drainage system rather than draining by gravity. That pump and its electrics, plus tiling, plumbing and fittings, make wet rooms a significant addition to the fit-out rate.
Can I keep the fit-out cost down?
Yes, the fit-out is the most flexible part of a basement budget. Keeping it as a plain habitable room with simple finishes and no wet rooms holds the per-square-metre rate down, while bespoke joinery, designed lighting and a bathroom or kitchen raise it.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property. They are guidance, not a quotation.