How much does basement tanking cost?
Updated 6 October 2026 · prices for 2026
Typical cost to tank a cellar or basement (waterproofing only)
£1,110–£4,310
for 35 to 78 m² of wall and floor, tanking only, including VAT (£920–£3,600 + VAT)
About £26 a m² for tanking slurry and £46 to £52 a m² for a cavity drain membrane with its channel, before VAT. Prep, a sump pump and the finish on top are extra. Bricken's tanking prices are estimates.
Try it: price basement tanking in Bricken
Typical UK rates and markup. Your own rates and prices live in your account.
This is a small part of Bricken. In the app you price the whole job in one place, or start from an extension or loft starter that puts every item in for you, then send your client a quote with a programme, stage payments and a PDF.
Save this as a full quote, with a programme, stage payments and a client PDFWith the code FOUNDER your first month is free, with everything unlocked and no card.
Basement tanking costs about £32 a m² including VAT with a tanking slurry and £55 to £62 a m² with a cavity drain membrane and its drainage channel, in 2026. Before VAT that's about £26 and £46 to £52 a m². Tanking a 4 × 4 m cellar, walls and floor, about 51 m², comes to about £2,879 including VAT with a membrane (£2,399 before VAT), or £1,614 with slurry (£1,345 before VAT). That's the waterproofing layer only. Hacking off old plaster, a sump and pump, and the finish on top (battens and plasterboard on the walls, a screed or floor over the membrane) are priced separately.
Tanking means keeping water out of a room that's partly or wholly below ground. There are two common ways. A cementitious slurry is a waterproof cement coating brushed on in two coats, and it holds the water back. A cavity drain membrane is a dimpled plastic sheet plugged to the walls and laid on the floor. It lets the water through the wall and leads it behind the sheet to a channel round the edge of the floor, and from there to a sump or drain. In BS 8102, the British Standard most designers work to, the first is called barrier protection (type A) and the second drained protection (type C).
What's in the price
We priced the membrane on a 4 × 4 m cellar with walls 2.2 m high, 51 m² of wall and floor, and 16 m of channel. This is where the money goes, before VAT.
- Membrane: 56 m², with 10% for laps and cuts, plugs and seals included, £1,313.
- Fixing it: about 20 hours, £551.
- Perimeter channel: 17 m, £398, and about 5 hours to lay it, £138.
Materials are about 71% of the price and labour 29%. Slurry is more evenly split. On the same cellar it's £1,345, about half materials and half labour, because two coats by brush take half an hour a m².
Price by cellar size
| Cellar | Area | Slurry | Membrane and channel |
|---|---|---|---|
| 4 × 4 m, walls only | 35 m² | £923 | £1,812 |
| 4 × 4 m, walls and floor | 51 m² | £1,345 | £2,399 |
| 5 × 6 m, walls and floor | 78 m² | £2,057 | £3,595 |
All before VAT, with walls 2.2 m high and the channel run round the whole floor. Add 20% for VAT.
Pricing it as a builder
The tanking itself is a straight rate per m², and it's rarely where a basement price goes wrong. The prep and the water are. Measure the walls and the floor separately, price the channel by the metre (about £33 a metre on our job), and then price everything round it as its own items.
Check five things on the site visit. What's on the walls now, because old plaster, paint or bitumen has to come off before slurry will bond. Where the water will go with a membrane, a sump and pump or a drain low enough to fall to. Whether water is running in now, which is a job for a specialist before anyone tanks over it. How much headroom there is once the floor build-up goes in. And whether the room will be lived in, which brings building control in and usually means the waterproofing is designed first.
Bricken's tanking prices are estimates rather than a merchant's list price, so check the membrane, channel and slurry against your own supplier before you send the quote.
Priced on its own, a job like this carries a small premium for travel, setting up, a minimum charge and part-used materials. Done as an extra while you're already on site, the same work usually costs a bit less.
How we priced it
We built the job in Bricken, the quoting app for UK builders, item by item. Bricken's estimated prices for the slurry, membrane and channel, a typical hourly rate (£20 an hour for a general builder, before markup), and a typical builder's markup of 30% on materials and 35% on labour. Your builder or a tanking specialist will price it at their own rates, so get a few quotes.
Priced in Bricken at standard UK rates (35 m² of slurry for the low figure, 78 m² of membrane with its channel for the high). Each figure is then multiplied by Bricken's regional factor, from 0.90 in the North East to 1.30 in inner London. The factors come from public 2025-26 build-cost guides and our own quotes. Where a region covers two areas, the low uses the lower factor and the high the higher. The factors are set for whole building jobs, so treat small differences as a guide.
Cost by region
| Region | 35 m², slurry | 78 m², membrane |
|---|---|---|
| London | £1,330£1,108 | £5,610£4,674 |
| South East | £1,240£1,034 | £4,830£4,027 |
| East of England | £1,160£969 | £4,530£3,775 |
| Midlands | £1,070£895 | £4,310£3,595 |
| North West | £1,050£877 | £4,100£3,416 |
| North East and Yorkshire | £1,000£831 | £4,100£3,416 |
| South West | £1,160£969 | £4,530£3,775 |
| Wales | £1,020£849 | £3,970£3,308 |
| Scotland | £1,110£923 | £4,310£3,595 |
What pushes the price up or down
Up
- A membrane instead of slurry: £2,399 against £1,345 on the 4 × 4 m cellar, about £1,054 more. It's often chosen where water comes in under pressure or the room will be lived in.
- The perimeter channel: £533 on 16 m, about £33 a metre.
- Small cellars: a membrane with its channel comes to £52 a m² on 35 m² against £46 on 78 m², because the channel is a bigger share of a small room.
- Prep: hacking off old plaster, cleaning and repairing the walls and filling cracks aren't in these figures.
- A sump and pump: a drained membrane needs somewhere to send the water, and that isn't in these figures either.
- London: about 20% to 30% more, from Bricken's regional factors.
Down
- Slurry: about £26 a m² before VAT, roughly half the membrane price, where your designer says a barrier is enough.
- Walls only: if the floor doesn't need it, slurry on the walls of a 4 × 4 m cellar is £923 instead of £1,345 with the floor.
- Bigger rooms: the channel and the setting out are spread over more m².
- An empty cellar with easy access: less time carrying materials and moving things round.
Questions
What's the difference between tanking slurry and a cavity drain membrane?
Slurry is a waterproof cement coating brushed on in two coats. It holds the water back. A membrane is a dimpled plastic sheet plugged to the wall. It lets water through the wall and leads it down behind the sheet to a channel and on to a sump or drain.
How much does it cost to tank a small cellar?
For a 4 × 4 m cellar with walls 2.2 m high, walls and floor come to about 51 m². In Bricken that's £1,345 before VAT with slurry and £2,399 with a membrane and 16 m of channel, before prep, a pump or finishes.
Do I need a sump pump?
With a cavity drain membrane the water it collects has to go somewhere. That's usually a sump and pump, unless there's a drain low enough to fall to. Slurry doesn't need one. A pump isn't in our figures.
How long does tanking take?
The 51 m² membrane job has about 25 hours of work in it, around three days for one person. Slurry on the same cellar is about the same, at half an hour a m² for two coats, plus drying time between coats.
Do I need building regulations to convert a cellar?
Turning a cellar into a room you live in usually needs building regulations approval, and sometimes planning. Check with building control and the council before you start, and get the waterproofing designed.
Is VAT included?
The big figures include VAT at 20%. If your builder isn't VAT-registered, the price before VAT is closer to what you'll pay.
Related guides
How we price: each figure is a Bricken quote built from the sizes, at standard UK merchant prices and day rates, with a typical builder’s markup. Your builder’s price will differ: get quotes.