Survey finding
Tanking failure in a basement: what it means and what to do
Tanking failure in a basement or cellar is a costly but contained finding. This page covers Type A/B/C waterproofing, what fixing it costs, and how lender and insurer markets treat it.
Last updated: 6 May 2026. Editorially reviewed: 20 May 2026.
Finding
Tanking failure in basement
What this usually means
Tanking is a waterproof barrier applied to basement walls and floors to keep groundwater out. Most UK tanking is either Type A (cementitious render) or Type C (cavity drained membrane). Failure shows as efflorescence, damp patches, blistering paint, or visible water ingress at the foot of walls. The cause is usually age, original installation defect, or hydrostatic pressure exceeding the tanking's design limit.
Why it matters
Basement tanking failure is rarely a structural risk to the property but is expensive to remediate and disruptive, often requiring full strip-out and re-tanking. BS 8102 sets out the design standards. Lenders rarely refuse but may impose a retention if remediation is required before basement use.
Ask your surveyor
- Check:What type of tanking is in place, A (cementitious), B (structurally integral), or C (cavity drained)?
- Check:Where are the visible failure points and what is the most likely cause?
Ask the seller
- Check:When was the tanking installed and which system?
- Check:Are there any guarantees from the original installer?
Next steps
- •Get two written quotes from local trades before negotiating with the seller.
- •Speak to your mortgage broker before exchanging if the finding affects mortgageability.
Browse all findings
- Spray foam insulation
- Evidence of movement
- Damp
- Japanese knotweed
- Damp proof course issues
- Underpinning
- Cracks
- Roof issues
- Timber decay
- Electrical issues
- Non-standard construction
- Asbestos containing materials
- Roof covering needs repair
- Single skin wall construction
- Timber decay / wet rot
- Settlement cracks
- RAAC concrete
- Wall tie failure
- Party wall matters
- Drainage issues
- Subsidence monitoring
- Full electrical rewire needed
- Flat roof condition
- Cladding issues
- EWS1 form required
- Lintel failure
- Structural crack BRE category 3
- Structural crack BRE category 4-5
- Chimney stack movement
- Chimney flashing failure
- Parapet wall movement
- Bay window cracking
- Flat roof ponding
- Cold roof inadequate ventilation
- Warm roof insulation issues
- Prefab concrete construction
- Large panel system (LPS) construction
- Rising damp
- Penetrating damp
- Condensation vs damp distinction
- Dry rot (Serpula lacrymans)
- Woodworm
- Timber floor springiness
- Cellar / basement damp
- Outdated electrics (60-amp fuse board)
- Aluminium wiring
- Partial rewire needed
- Gas boiler condition
- Back boiler
- Unvented hot water cylinder issues
- Lead pipes (pre-1970)
- Lead paint
- Asbestos in Artex ceilings
- Asbestos floor tiles
- Asbestos cement roof
- Asbestos insulated board (AIB)
- Asbestos soffit boards
- Pointing / repointing needed
- Render cracking
- Pebbledash delamination
- UPVC window seal failure
- Sash window condition
- Flat roof membrane condition
- Zinc roof
- Felt roof condition
- Corrugated asbestos roof
- Cavity wall insulation issues
- External wall insulation issues
- No building regulations certificate
- No planning permission for extension
- Certificate of lawfulness needed
- Indemnity insurance required
- Neighbour dispute on file
- EPC F or G rating
- Oil heating property
- Off-gas-grid property
- Solar panel lease vs owned
- Ground source heat pump property
- Air source heat pump property
- Chimney breast removed without support
- Floor joist decay
- Wall bowing
- Mould and condensation
- Septic tank property
- Thatched roof condition
- Listed building restrictions
- Conservation area restrictions
- Restrictive covenants on title
- Coal mining area
- Coastal erosion risk
- Flood risk zone 3
- Radon affected area
- Contaminated land history
- Trees near building
- Party wall agreement outstanding
- EICR required
- Knotweed treatment history
- Single glazing condition
- RCD protection missing
- Damp-proofing guarantee transferability
- PRC (precast reinforced concrete) house
- Airey house
- BISF (British Iron and Steel Federation) house
- Timber frame construction
- Steel frame house
- Wet rot
- Heave (ground movement)
- Chimney condition and stability
- Short lease (under 80 years)
- Fire safety: flat and leasehold issues
- Blocked or condemned flue
- Spalling brickwork
- Diagonal cracks in walls
- Retaining wall condition
- Tanking failure in basement
- Missing or slipped ridge tiles
- Lead flashing condition
- Gutters and downpipes
- Double glazing condensation (failed units)
- Skylight or roof light condition
- Dormer condition and weathering
- Torn or missing sarking felt
- Chancel repair liability
- Easement or right of way
- Boundary dispute or unclear boundary
- Adverse possession risk
- Flying freehold
- Ground rent escalation clause
- High or variable service charge
- Extension without planning consent
- Loft conversion: no building regs
- Single-phase electrical supply only
- Shared or private sewer
- Blocked or collapsed drains
- Cesspit or septic tank
- Solid fuel heating
- No mains gas supply
- Low water pressure
- Private water supply
- Wimpey No-Fines concrete house
- Reema construction
- Unity or Boot construction
- Laing Easiform
- Cornish Unit house
- Cross-wall construction
- In-situ concrete construction
- Oak frame construction
- Radon: mitigation required
- Missing or inadequate fire alarms
- Single staircase: means of escape
- No earthing or bonding
Tool shortcut
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What you need to know
Severity
Significant. Specialist follow-up usually warranted before exchange.
Typical cost to fix
Specialist damp-proofing inspection £150–£400. Patch tanking repair: £600–£1,800. Full re-tanking of a typical UK basement: £8,000–£25,000 depending on size and Type A/B/C system specified. Cavity drained membrane systems with a sump pump add £2,000–£5,000.
Mortgage impact
Most lenders accept tanking findings if remediation is quoted and the basement is not the only habitable space. Basements counted in the property's habitable square footage may trigger a retention until cover is documented.
Insurance impact
Tanking failure is wear-and-tear, not an insured event. The pump and electrics for cavity drained systems are typically the insured items.
When to pull out
Pull out only if the basement is fundamental to the purchase price, full re-tanking cost is high, and the seller refuses to fund or deduct.
When to renegotiate, and by how much
Get a specialist quote for re-tanking to BS 8102 spec. Negotiate on quote plus 15–20% buffer.
Thinking of pulling out or renegotiating? What to do after a bad survey
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Check the property before you offer
Flood, subsidence, EPC, crime, schools, transport, broadband, tenure, age, listed status and price checks where data is available.
Run a free previewRead next
Cellar / basement damp , often sits near tanking failure in basement on a survey and is the next thing to check.
Editorial review
Editorial owner: BiteRight Ltd, operator of MyPropertyScan. We review buyer guides against UK public property datasets, RICS survey wording, lender requirements, and common buyer questions.
Pages are updated when source coverage, property-risk guidance, survey cost assumptions, or product checks materially change. Methodology and dataset limitations are explained on the MyPropertyScan methodology page.
Sources used
We use UK public and specialist sources where they are available. Public datasets can be incomplete, delayed, or missing for some addresses. Treat them as a starting point, not as a replacement for professional advice.
Source standard: preference goes to official government datasets, statutory bodies, professional standards, and primary dataset publishers. We cite the source family on the page and explain coverage limits rather than filling gaps with unsupported estimates.