Summary

Tanking is a narrow, specialist slice of the wider basement conversion trade, and it's routinely mispriced by two different groups for two different reasons. General builders undercharge it because they treat it as "another coat of something on the wall" and don't allow for surface preparation time, junction detailing, or the sump/pump commissioning that a proper Type C job needs. Waterproofing specialists sometimes overcharge relative to material cost because the job is quoted on risk rather than labour hours — which is actually the more defensible approach, since a tanking failure is one of the most expensive callbacks in the trade.

This guide is about pricing the tanking work itself — labour, materials and margin — as distinct from basement conversion pricing guide, which covers the full £3,000–£5,000/m² basement conversion job (underpinning, drainage, MVHR, finishes, the lot). If you're pricing a standalone damp cellar that needs waterproofing before it becomes usable storage, or you're a specialist subcontractor quoting the waterproofing package within someone else's basement conversion, this article is the one to use. For the underlying system selection and technical detail — Type A, B, C, and BS 8102:2022 grades — see tanking and the fuller technical breakdown in bs 8102 waterproofing types.

The single biggest pricing risk in this trade is scope creep at the floor/wall junction and around service penetrations, both of which are where tanking systems actually fail. Price these properly from the outset rather than treating them as included extras, and separate material cost, labour, and risk margin clearly in the quote so the customer understands why waterproofing costs what it does.

Key Facts

Quick Reference Table

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System Typical Cost (£/m², supplied + fitted) Labour Share Material Share Best Suited To
Type A — cementitious render £50–£80 ~55% ~45% Sound masonry, Grade 1–2, budget-conscious jobs
Type A — crystalline slurry £30–£60 ~50% ~50% Sound concrete with active seepage, hairline cracks
Type A — bituminous (external) £60–£100 (excl. excavation) ~40% ~60% External tanking where excavation access exists
Type C — cavity drain membrane £100–£150 ~60% ~40% Grade 2–3, high water table, rubble stone walls
Dual system (A + C) £120–£180 ~55% ~45% Grade 3 habitable — BS 8102:2022 recommended default
Sump + single pump £450–£950 (fixed cost, not per m²) — — Small cellar, one collection point
Sump + duty/standby twin pump + battery £2,500–£5,500 (fixed cost) — — Full basement conversion, Grade 3
CSSW survey + spec £400–£900 (fixed cost) — — Any Grade 2+ scheme
10-year IBG warranty 5–12% of contract value — — PCA/BWPDA member jobs, mortgage-relevant conversions

Detailed Guidance

Pricing a Type A internal cementitious job from a wall survey

Walk the space with a moisture meter and note: substrate type (block, brick, stone, poured concrete), condition (sound vs. friable, cracked, previously coated), and any active water ingress. Preparation is where most quoting errors happen — a wall that looks "just needs a coat on it" often has failed paint, gypsum plaster, or efflorescence that must be hacked back to bare masonry first. Price preparation as a distinct line: hacking back adds roughly £15–£30/m² and materially increases labour time versus a clean substrate.

Worked example — 25m² cellar wall area, sound brick substrate, Grade 2 use (workshop/storage):

Pricing a Type C cavity drain job with sump and pump

Type C is priced per m² of membrane area (walls and floor) plus a fixed cost for the sump and pump package, because the pump doesn't scale linearly with wall area. Always separate these two cost lines in the quote — customers frequently ask to remove the pump to save money, not realising it's the part of the system that actually manages the water, not an optional extra.

Worked example — 30m² floor, 45m² wall area (75m² total membrane area), Grade 3 habitable conversion:

This aligns with the £100–£150/m² Type C benchmark once the fixed-cost items (sump, CSSW, contingency) are absorbed into the overall figure — always sense-check a fixed-cost-heavy quote against the £/m² benchmark to catch under- or over-pricing.

Pricing a dual system for Grade 3 habitable use

BS 8102:2022 recommends combining two different system types for Grade 3 habitable spaces, because no single system is considered fully reliable in isolation — see bs 8102 design principles for the underlying design rationale. In practice this usually means a Type C cavity drain as the primary system with a Type A cementitious backing coat, or a Type B structurally integral concrete design combined with Type C — the latter only applies to new-build or major structural repair where the concrete mix itself is specified with waterproofing admixture.

Pricing a dual system is not simply the sum of the two individual systems' £/m² rates — there's overlap in preparation and access, so price it as its own line item (£120–£180/m²) rather than adding two full quotes together. Where a customer specifically wants the redundancy of two systems and asks why it isn't simply double the single-system price, explain that most of the labour (access, prep, junction detailing) is shared between the two coats.

Subcontracting vs. doing it in-house

If you're a general builder who doesn't hold CSSW qualification or PCA/BWPDA membership, the honest answer for any Grade 2+ job is to subcontract the waterproofing design and application to a specialist and mark up their invoice, rather than attempting to design and apply the system yourself. The insurance-backed guarantee that most customers expect on a basement conversion is only available through PCA/BWPDA member contractors — see bwpda pca membership — and a non-member installation, however competently executed, cannot access that warranty product. Mark-up on a specialist subcontractor's tanking package is typically 10–15%, reflecting your project management and coordination role rather than technical risk you're not carrying.

What goes wrong when tanking is underpriced

The most common underpricing mistakes, roughly in order of frequency:

  1. Measuring wall area net of the floor/wall junction and treating the junction as included — it needs its own line item and typically 1–2 hours per linear metre
  2. Quoting from a visual survey without a moisture meter reading, then discovering active water ingress once work starts (which may require a Type C retrofit instead of the Type A originally quoted)
  3. Omitting the sump/pump maintenance contract, leaving the warranty unsupported and the customer unaware that pump failure = flooding
  4. Not accounting for service penetrations (pipes, cables passing through the tanked zone) — each one needs a specific detail and adds 30–60 minutes
  5. Pricing Grade 3 work at Grade 1/2 rates because the customer described the space informally as "just storage" when they actually intend a home office or bedroom later

Frequently Asked Questions

Can I quote tanking without a CSSW survey to save the customer money?

You can for a low-risk Grade 1 job (car parking, plant room) where the consequences of a defect are minor. For Grade 2+ work — anything the customer might eventually use as habitable space, or anywhere a warranty matters for resale or mortgage purposes — skipping the CSSW survey is a false economy. Insurers and warranty providers generally require CSSW design as a condition of the insurance-backed guarantee, and a system installed without one may be uninsurable regardless of how well it's fitted.

Why is Type C more expensive than Type A per m² when the material itself looks cheaper?

The HDPE membrane material cost is genuinely lower than repeated coats of cementitious slurry, but Type C requires more labour (mechanical fixing at 300mm centres with sealed fixings, perimeter channel installation, sump excavation) and a mechanical/electrical element (pump, alarm, battery backup) that Type A doesn't have. The £/m² figure for Type C also typically needs to absorb some of the fixed sump cost if it's being blended into a single rate — keep these separate in your quote wherever possible for clarity.

Should I price tanking by the day or by the m²?

Price small, well-defined jobs (a single cellar wall, a known substrate) by the m² using the benchmarks above. Price larger or uncertain jobs — particularly anything where the substrate condition can't be fully assessed until you open it up, such as old rubble stone walls — with a day rate plus materials, and a clearly stated provisional sum for unknowns. Converting a day-rate estimate to a fixed-price quote before the substrate has been properly assessed is the fastest way to lose money on this trade.

Does tanking need building control sign-off?

Not the tanking work in isolation, but if it's part of converting the basement to habitable use, the whole project needs Building Regulations approval — see basement conversion building regs for the relevant Approved Documents. Get this confirmed with the customer before quoting so the tanking specification matches what building control will expect for the intended use class.

Regulations & Standards