First, find out what happened
Ask for the engineer's reports, crack-monitoring records, drainage investigations, repair schedule, completion certificates and insurance correspondence. Put them in date order. You are trying to see when movement started, what cause was found, what work followed and whether anything changed afterwards.
The word subsidence is sometimes used loosely. Settlement in a new extension, thermal movement and a crack where two parts of a building meet are different matters. A surveyor or engineer can review the description against the building and the old records.
Look at the property insurance questionnaire and seller's forms as well. If one document calls the work “structural repairs” and another says “minor cracking”, ask for the difference to be explained.
A repaired crack is only part of the evidence
Decoration can hide a crack for a while. That does not prove the cause has gone. Equally, old underpinning does not mean a house is continuing to move. Good evidence might include monitoring that reached a clear conclusion, repairs aimed at an identified cause and a long period without further change.
Leaking drains, shrinkable clay affected by trees, shallow foundations and mining history call for different enquiries. If the existing file leaves a serious gap, your engineer may suggest new monitoring or tests. That can slow the purchase, but an unanswered structural question is not improved by rushing.
Look for dates on photographs and monitoring charts. A statement that cracks have been stable for “a long time” is far less useful than measurements taken over a stated period.
Bring the lender in early
Tell your mortgage adviser and lender what is known. The lender may ask for an engineer's report, proof that work was completed or confirmation that suitable insurance is available. Do this while you still have time to obtain missing papers.
Your conveyancer can ask about the claim, guarantees and responsibility for earlier work. Read any guarantee carefully. Who issued it? Can it be transferred? What repair does it cover? What happens if the original contractor no longer trades?
Tell the surveyor which documents the lender has requested. This can prevent you paying for a report that does not contain the wording or inspection the lender needs.
Get an insurance answer before exchange
Some homes with an old subsidence claim can be insured on fairly ordinary terms. Others attract a larger subsidence excess, limited cover or fewer quotes. The seller's existing insurer may be prepared to continue cover for a buyer, but there is no automatic right to this.
Give insurers the history they request and keep their answer in writing. Check that subsidence is included and read the excess and exclusions. A cheap quotation with subsidence removed may not satisfy the lender or protect you in the way you expected.
If the online quote asks a yes-or-no question that does not fit the history, call the provider. Keep a note of the answer and the name of the organisation that gave it.
Remember that you may sell the house one day
A future buyer will probably ask for the same file. Keep reports, invoices, photographs, guarantees and insurance papers together. Better records make the history much easier to explain.
Price matters too. Allow for any extra insurance cost, work still recommended and the possibility of a smaller pool of buyers later. Compare the house with unaffected properties you could buy for similar money.
Ask the estate agent how the price was set and how long the house has been for sale. That will not give you a valuation, but it may help when deciding what evidence and negotiation are needed.
A sensible position before you commit
By exchange, you should understand the likely cause, the repairs, the evidence of stability and any remaining uncertainty. Your lender must be satisfied and you need insurance on terms you can live with. If one of those parts is missing, pause and find out why.
Have your own adviser review the old paperwork. A report commissioned by the seller or an earlier insurer may have answered a different question from the one you need answered now.