Basement Tanking Cost UK
What it really costs to tank and waterproof a basement — cementitious tanking, cavity drain membranes and full BS 8102 systems, with indicative UK price ranges.
What Is Basement Tanking?
Tanking means applying a continuous waterproof barrier to basement walls and floors so groundwater cannot pass through. It is one of three waterproofing approaches under BS 8102:2022:
- Type A (barrier / tanking) — a cementitious slurry or membrane applied internally or externally.
- Type B (structurally integral) — the waterproof concrete structure itself resists water.
- Type C (drained protection) — a cavity drain membrane manages water to a sump and pump.
The right choice — and therefore the cost — depends on the water table, whether the space is habitable, and the condition of the structure. Most reliable basement waterproofing combines systems for redundancy.
Rule of thumb: Budget £50–£150/m² for the waterproofing system itself, with a typical full basement project running £8,000–£25,000+ once preparation, drainage, sump/pump and finishes are included.
Basement Tanking Cost by System
Cementitious Tanking (Type A)
Waterproof slurry applied to sound walls and floors. Lowest cost per m² but needs a structurally sound substrate and lower water pressure.
Cavity Drain Membrane (Type C)
Studded membrane that manages water to a drainage channel, sump and pump. The most reliable system for habitable basements and higher water tables.
External Tanking / Membrane
Waterproofing applied to the outside face. Highly effective but requires excavation, so total cost rises sharply on existing structures.
Full Basement Waterproofing Project Costs
| Project Type | Typical Scope | Indicative Cost |
|---|---|---|
| Small cellar tanking | Single room, cementitious tanking | £3,000 – £8,000 |
| Domestic basement (Type C) | Cavity drain membrane, sump & pump, habitable | £8,000 – £18,000 |
| Large / commercial basement | Combined systems, multiple pumps, BS 8102 design | £18,000 – £50,000+ |
| Waterproofing design specialist | BS 8102 design, drainage strategy, warranty | £750 – £3,000 |
Important: These ranges are indicative and exclude VAT. A site survey and BS 8102 waterproofing design are essential before budgeting a basement project.
What Affects Basement Tanking Cost?
- Water table & hydrostatic pressure — high groundwater pushes you toward drained (Type C) systems and pumps.
- Habitable vs storage use — habitable space demands a higher grade of waterproofing under BS 8102.
- Structural condition — cracks and failing joints need resin injection or repair before tanking.
- Access & excavation — external tanking on an existing basement is far more costly than internal systems.
- Pump redundancy & power — twin pumps and battery backup add cost but protect habitable basements.
How Much Does It Cost to Tank a Cellar?
Cellar tanking is priced on the same per-square-metre basis as basement tanking, but the numbers usually land lower because a cellar is smaller: as a rough guide, tanking a typical single-room cellar costs from around £3,000 to £8,000, rising to £8,000–£15,000+ where the space is being converted to habitable use with a cavity drain membrane, sump and pump. The system itself is still £50–£100/m² for cementitious tanking or £80–£150/m² for a Type C cavity drain membrane — the smaller area is simply spread over fewer metres.
What makes cellars different from purpose-built basements is rarely the size — it is the construction and the access. Most UK cellars sit under Victorian and period properties and are built in brick rather than concrete, often with lime mortar, uneven walls and historic dampness already present. That affects both method and cost:
- Brick substrates need careful preparation — old plaster, render and paint stripped back to sound masonry — before a tanking slurry will bond, and a cavity drain membrane is frequently the safer choice because it manages water rather than relying on adhesion to an irregular wall.
- No external access is the norm: you cannot excavate around a cellar under an occupied terraced house, so waterproofing is almost always applied internally, which rules out the cheapest external options.
- Restricted access and headroom — narrow stairs, low ceilings and no direct route for materials and spoil — slow the work and push up labour per square metre.
- Existing damp and salts in old brickwork may call for salt-neutralising treatment or a membrane system that tolerates residual moisture.
For these reasons the cheapest way to tank a cellar is not always cementitious slurry: on an irregular brick cellar a cavity drain membrane often proves more reliable and more cost-effective over its life, because it does not depend on a perfect bond to resist water pressure. The only way to price a cellar accurately is a survey — the water table, the state of the brickwork and the intended use drive the figure far more than floor area alone.
MPS Concrete Solutions is based near Cambridge and tanks cellars and basements across Cambridgeshire, London and the wider UK, for both period homes and commercial buildings. Every enquiry starts with a free assessment and a BS 8102-compliant recommendation.
Which Tanking System You Actually Need
The cheapest rate per square metre is not the cheapest job if the system cannot cope with the conditions. Four things decide it, and a surveyor should be able to tell you all four on one visit.
| Your situation | Normally specified | Why |
|---|---|---|
| Sound concrete walls, low water table, storage use only (BS 8102 Grade 1) | Cementitious tanking (Type A), £50–£100/m² | The slurry becomes part of the substrate. It needs a sound, even background and modest water pressure to work. |
| Habitable conversion, or any space where a damp patch is unacceptable (Grade 3) | Cavity drain membrane (Type C), £80–£150/m² | It manages water rather than resisting it, so it does not fail if the wall develops a crack. Needs a sump, pump and maintenance access. |
| Irregular brick or lime-mortar cellar under a period property | Cavity drain membrane (Type C) | A slurry depends on a continuous bond to resist pressure; on uneven historic brickwork that bond is the weak link. |
| High water table, or pressure already pushing water through a joint | Resin injection first, then Type A or C | Sealing the live path comes before the barrier. A coating applied over a running leak will be pushed off. |
| Accessible external face, new build or major refurbishment | External tanking plus land drain, £90–£180/m² plus excavation | Intercepting water before it reaches the structure is the most robust option — when excavation is actually possible. |
BS 8102:2022 encourages combined protection — two systems rather than one — wherever the consequence of failure is high. On a habitable basement that usually means Type A plus Type C, and the cost is closer to additive than to the higher of the two. It is also the reason a single-system quote and a combined-system quote for the same room can differ by 60% and both be honest.
Five Things Cheap Tanking Quotes Leave Out
Comparing tanking quotes is difficult because the headline rate covers different amounts of work. These are the exclusions that turn a £6,000 quote into a £9,000 invoice, and they are all worth asking about in writing before you appoint anyone.
- Preparation and making the substrate sound. Hacking off defective render, removing laitance, cutting out loose mortar joints and repairing spalled concrete all come before the system goes on. If a quote prices the membrane but not the preparation, it is pricing half the job.
- The wall-to-floor junction. A fillet seal — a 25–50 mm cove of mortar run around every wall-to-floor and wall-to-wall angle — is the detail that lets the waterproofing turn the corner without thinning or tearing. It is the commonest place a tanked basement weeps, and the commonest line item missing from a cheap quote.
- Service penetrations. Every pipe, duct and cable passing through the wall is a hole in the waterproofing and has to be sealed as a designed detail, not filled with mortar. Count them before you compare quotes.
- The pump, its power supply and its back-up. A Type C system without a sump and pump is not a system. A habitable basement normally needs a dual-pump sump with a battery back-up and a high-level alarm, because the consequence of a power cut is a flood, and that assembly is a four-figure item on its own.
- Maintenance access and the warranty conditions attached to it. Type C protection has to stay accessible — if the pump cannot be reached, the warranty normally lapses. Ask what the warranty actually covers, who underwrites it, and what inspection regime it requires.
One more thing worth knowing: the system cost is often the smaller half of a basement conversion. Reinstating the floor, insulation, plastering, electrics and a means of escape typically costs more than the waterproofing, and a waterproofing specification signed off before the fit-out is designed will save money against one retro-fitted afterwards.
Reviewed by Jerry Blears, Director (LinkedIn), MPS Concrete Solutions. Last reviewed October 2026.
Frequently Asked Questions
How much does basement tanking cost in the UK?
Basement tanking typically costs £50–£100/m² for cementitious (Type A) tanking and £80–£150/m² for a cavity drain membrane (Type C) system including a sump and pump. A complete project commonly ranges from £8,000 to £25,000+ depending on size, water table, structural condition and specification.
What is the cheapest way to tank a basement?
Cementitious tanking slurry is usually the lowest cost per m², but it suits structurally sound substrates and lower water pressures only. For habitable space or higher water tables, a cavity drain membrane is more reliable and often more cost-effective over its lifetime.
What is tanking a basement?
Tanking applies a continuous waterproof barrier — a cementitious slurry or membrane — to basement walls and floor so water cannot pass through. It is one of three approaches under BS 8102, alongside structurally integral (Type B) and cavity drainage (Type C) waterproofing.
Does basement tanking need to comply with BS 8102?
Yes — below-ground waterproofing should be designed to BS 8102:2022, which sets grades of protection and the role of a waterproofing design specialist. Compliant design is essential for habitable space and for warranties.
How much does it cost to tank a cellar in the UK?
Tanking a typical single-room cellar costs from around £3,000 to £8,000, rising to £8,000–£15,000+ where it is being converted to habitable use with a cavity drain membrane, sump and pump. The per-m² rate is the same as for a basement — £50–£100/m² for cementitious tanking or £80–£150/m² for a Type C membrane — but the smaller area keeps the total down. Because most cellars are brick-built under period properties with no external access, the brickwork condition, the water table and restricted access drive the final figure as much as floor area, which is why a survey is the only way to price one accurately.
Get a Basement Waterproofing Quote
MPS Concrete Solutions provides BS 8102-compliant basement tanking and waterproofing across the UK, with free initial assessments for commercial and residential clients.
