Buying a house with past subsidence: what to check before you exchange

Historic or active: the question that matters

The HomeOwners Alliance splits it into two cases: historic movement that has stopped or been repaired, and active movement that is still happening. If your surveyor suspects subsidence, HOA’s advice is to get a structural engineer to inspect before you go further (HOA).

RICS says cracks may need measuring and monitoring for as long as 12 months, and that there is rarely cause for real concern unless cracks appear suddenly and are more than 3mm wide (RICS subsidence guide). Most houses have cracks. Our crack severity checker and the guide to subsidence, settlement or thermal movement help you tell them apart.

What caused it, and has the cause gone?

RICS lists three usual causes. Each points to a different fix:

• Trees on shrinkable clay. The most common cause by the Which? estimate RICS quotes. Removing or managing the tree can solve it, though RICS notes that occasionally removing a tree makes things worse, so this needs proper advice.
• Leaking drains or water mains washing out or softening the soil. RICS says repairing the pipework is usually enough to stabilise the house without underpinning. Ask whether a drain CCTV survey was done and what was repaired.
• Mining. Historic coal mining can cause ground movement that is much harder to fix. RICS suggests checking whether the property is in a former coal mining area and ordering a mining report if it is (see the Coal Authority).

RICS also notes that investigating and fixing subsidence can take up to two years, so find out where in that process the house is.

The paperwork to ask for (through your conveyancer)

• Details of any insurance claim: when, the cause, and what the insurer did.
• Structural engineer’s reports and any crack-monitoring results.
• The Certificate of Structural Adequacy, or equivalent sign-off, once repairs were completed.
• Details and guarantees for any underpinning, plus Building Control sign-off where applicable.
• Drain survey and repair records if leaking drains were the cause.
• Whether the seller’s insurer will continue cover for a new owner. Ask, but don’t assume a policy transfers.

Insurance: sort it before you exchange

The ABI says buildings insurance will normally cover damage caused by subsidence, heave or landslip, with an excess you pay first (ABI guide to dealing with subsidence). RICS says that excess is commonly £1,000. The practical risk for a buyer is finding cover at a sensible price once a subsidence history is declared, so get a real quote for this specific address before you commit. Our guide does subsidence affect your home insurance? goes into declarations, specialist insurers and what underpinning does to premiums.

If you later switch buildings insurer and a subsidence problem then appears, an ABI agreement between insurers decides who handles the claim. The previous insurer handles it if it’s reported within eight weeks of the new policy starting. Between eight weeks and a year, the insurer you notify handles it and the two insurers share the cost. After a year, it’s the new insurer. The agreement covers a change of insurer, not a change of owner, so it doesn’t help with the handover when you buy. That’s why the pre-exchange insurance quote and the seller’s paperwork matter.

What repairs typically cost

The ranges vary enormously, because the fix depends on the cause:

Don’t accept an underpinning scheme until the cause is known and the movement has been monitored. RICS notes that the Institution of Structural Engineers recommends underpinning only as a last resort. Read when you actually need underpinning before accepting a scheme. If the numbers don’t work, should I pull out after a bad survey? covers when to walk.