Start with what has actually changed
Compare the current layout with similar houses nearby and any older floor plan you can find. A wide opening may indicate a removed wall. A loft staircase, lowered ceiling, boxed-in beam or unusual floor level can show where work has been carried out. Ask the seller when each alteration was made and who designed it.
Do not assume that a room called a bedroom has approval to be used as one. Estate-agent descriptions are not building-control decisions. Measure headroom, look for a proper staircase and note escape arrangements. Your surveyor and conveyancer need a clear list of the work, especially when several owners have altered the property over time.
Look closely where old and new meet
Small hairline cracks at a junction are common because materials and foundations move differently. Wider, stepped or changing cracks deserve closer attention, particularly where doors stick, floors slope or water is entering. Photograph the area and ask whether the crack is recent. Fresh filler along one neat line can be worth mentioning to the surveyor.
Check roof flashings, gutters and thresholds around an extension. Rain often finds weak details at junctions. Inside, look at ceiling edges, corners and flooring for staining or movement. One dry viewing cannot show how the addition behaves in prolonged rain, so ask about earlier leaks and check any repair paperwork.
Ask for the right permissions and records
Depending on the work, the file may contain planning permission, a lawful-development certificate, building-control approval, party-wall records, structural calculations or a warranty. Not every project needs every document. Ask your conveyancer what should exist for this alteration and what a missing item means now.
Planning and building regulations do different jobs. Planning deals mainly with the acceptability of development, while building control addresses construction standards. Approval on a council website does not prove that completion was signed off. An indemnity policy may cover a limited legal risk; it does not repair poor workmanship or confirm that the structure is safe.
A loft room needs safe access and escape
Look beyond the attractive sloping ceiling. Check the staircase, guarding, doors, smoke alarms, windows and headroom. Ask whether the floor structure was strengthened and how the roof was altered. Storage boards placed over ceiling joists are not the same as a properly designed habitable floor.
Insulation and ventilation also matter. Condensation can develop where warm air reaches a cold roof space, while tightly packed insulation can block eaves ventilation. A surveyor may not be able to inspect every concealed area. If records are poor or visible work raises concern, a structural engineer or suitably qualified specialist may be needed before you commit.
Check drainage, heating and insulation in additions
An extension can change the route of drains and rainwater. Lift accessible covers with permission and ask where new sinks, bathrooms and downpipes connect. A public sewer beneath an addition can involve permissions that your conveyancer should examine. Slow drainage or repeated repairs justify a closer look.
Notice whether the new space heats evenly and whether radiators seem adequate. Large areas of glazing may make it hot in summer and cold at night. Ask for the Energy Performance Certificate and any insulation details, though the lived result matters too. A pleasant room on a mild afternoon may be expensive to keep comfortable through winter.
Put the findings into the price decision
Missing papers do not always mean the purchase must stop. First establish what is missing, what physical risk remains and whether the lender or insurer has requirements. Your conveyancer, surveyor and mortgage adviser may each see a different part of the problem, so pass relevant information between them.
Price any necessary investigation and urgent work before exchange. Do not base a reduction on the most alarming possible outcome if there is no evidence for it. Equally, do not accept “it has been there for years” as proof. A sensible decision rests on the present condition, available records and the cost of dealing with the uncertainty you would take on.
Ask whether the altered space has been included in the lender’s valuation on the same basis as the rest of the home. If it has been excluded or made subject to a condition, settle that point before renegotiating the price.