Buying Guide
Cob house survey: damp, render, roof and mortgage checks
Cob houses need specialist survey judgement because they do not behave like brick or blockwork. Cob is strong when kept dry and breathable, but vulnerable when cement render, poor drainage, leaking roofs or raised external ground trap moisture in the wall.
Last updated: 6 May 2026. Editorially reviewed: 20 May 2026.
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Run a free previewWhat makes this property type distinctive
Cob is an earth-wall construction, usually thick, breathable and often finished with lime render or limewash. It is common in Devon, Cornwall, Dorset and parts of the West Country. Many cob houses are listed or in conservation areas, and repairs should use compatible materials rather than modern cement-based systems.
Common defects to expect
These items are routine for the property type. Most are renegotiation items, not deal-breakers. The survey's job is to flag which apply to this specific property and which have already been addressed.
- Cement render trapping moisture against cob walls
- Raised external ground levels bridging the wall base
- Insufficient roof overhang or failed gutters saturating walls
- Erosion at the plinth or base of walls
- Damp and mould from sealed internal finishes
- Historic movement or bulging where cob has softened
- Inappropriate injected damp-proof course treatments
- Listed-building restrictions on repair materials and finishes
What the survey should cover
- Wall material confirmation and condition of cob, plinth and render
- Moisture sources: roof, gutters, ground levels, drains and cement finishes
- Roof overhang, thatch or tile condition and rainwater goods
- Evidence of wall bulging, erosion, cracking or past structural repair
- Breathability of external render and internal finishes
- Listed-building, conservation-area and insurance implications
Which survey level to book
RICS Level 3 is essential, ideally from a surveyor with cob or historic earth-building experience. If the surveyor is not confident with cob, commission a specialist conservation survey before exchange.
For a deeper comparison see Level 2 vs Level 3 survey.
Construction-specific risks
Cob risk is moisture management. A cob house can last for centuries when water is kept off and vapour can escape. Modern cement render, impermeable paint, hard landscaping against walls and poor gutters can cause more damage than age alone.
What to check before offering
- →Ask whether the walls are cob throughout or mixed with later block or brick additions
- →Check render type and whether cement render has been used
- →Inspect external ground levels, drains, gutters and roof overhangs
- →Confirm listed-building status and restrictions on repair materials
- →Get insurance and lender comfort before committing to survey spend
Use the full pre-offer checklist on the house buying checklist to combine these property-type checks with the standard pre-offer items.
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Run a free previewFrequently asked questions
Are cob houses hard to mortgage?
Some mainstream lenders accept cob with a satisfactory specialist survey and insurance. Others treat it as non-standard construction. Broker and lender confirmation before survey spend is sensible.
What is the biggest defect on a cob house?
Moisture trapped in the wall, often from cement render, raised ground levels, failed gutters or poor drainage. Cob is durable when dry and breathable; it deteriorates when water cannot escape.
Can I use modern damp-proofing on a cob house?
Usually no. Chemical DPC injection and cementitious tanking are commonly inappropriate. Repairs should be specified by someone who understands breathable historic fabric and lime-based materials.
Do cob houses need Level 3 surveys?
Yes. A Level 3 survey by someone with historic-building experience is the minimum. For visible damp, bulging or cement render, get specialist conservation advice before exchange.
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.
General information only. Not legal, mortgage, insurance, or surveying advice. Always confirm with your own surveyor, broker, and conveyancer before making decisions. MyPropertyScan is operated by BiteRight Ltd.