Survey finding
Blocked or collapsed drains: what to do
Drain issues are one of the more expensive sleeper findings on UK surveys. This page covers CCTV drain surveys, no-dig lining vs excavation, and the link to subsidence on clay soils.
Last updated: 6 May 2026. Editorially reviewed: 20 May 2026.
Finding
Blocked or collapsed drains
What this usually means
Drain blockages and collapses range from a localised root intrusion or fatberg to a fully collapsed clay pipe needing excavation and replacement. Older clay pipes (pre-1970) are vulnerable to root ingress and joint failure. Surveyors don't routinely lift manholes; a CCTV drain survey by a specialist is the standard follow-up where drainage is suspect.
Why it matters
A collapsed drain underground is one of the more expensive sleeper issues, the works often involve excavation in driveways or gardens. Lenders rarely refuse on drains alone but may impose retentions where structural movement is also suspected (drain leaks can cause subsidence on clay soils).
Ask your surveyor
- Check:Did you lift any manhole covers, and what was visible?
- Check:Are there signs of subsidence or dampness near drain runs?
Ask the seller
- Check:When were the drains last inspected, cleared, or repaired?
- Check:Have there been any blockages or backups in the last 5 years?
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
CCTV drain survey: £200–£500. Localised drain unblocking: £150–£400. No-dig drain lining (where viable): £1,200–£4,000 per run. Excavate and replace section of clay drain: £2,500–£8,000+.
Mortgage impact
Standard for most lenders. Combined with structural movement, may trigger a retention.
Insurance impact
Standard subsidence cover usually responds where a drain leak has caused movement. Drain repair itself is often excluded.
When to pull out
Pull out only if multiple drain runs have collapsed, structural movement is also evident, and the seller refuses to engage.
When to renegotiate, and by how much
Get a CCTV drain survey before exchange (£200–£500). Negotiate on the specialist's quoted remediation plus 15–20% buffer.
Thinking of pulling out or renegotiating? What to do after a bad survey
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The Survey Decoder explains the wording. The full report adds address-specific flood, subsidence, EPC, crime, listed status, building age and price comparison data, so a single finding isn't judged in isolation.
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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
Drainage issues , often sits near blocked or collapsed drains 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.