How much value does an extension add?
A well-built single-storey extension typically adds 5 to 15 percent to a property's value in Fulham. The return is strongest where it creates a genuinely better plan — a full-width kitchen-dining space — rather than simply adding floor area to an already awkward layout.
In Fulham, where price per square metre is high, added space is generally recovered on sale. A side return infill costing £70,000 to £90,000 on a house worth £1.2m is roughly 6 to 8 percent of value, and a good one typically returns at or above that. But the correlation is with quality of plan, not area: buyers pay for a light, well-proportioned family space, not for square metres in the abstract.
The extensions that return least are those that solve nothing. Extending into the garden without addressing a dark middle room, or adding space that makes the remaining garden unusable, can leave a house harder to sell rather than easier. On small Fulham plots the garden that is lost has real value, and there is a point past which extending reduces the appeal of the house.
As with lofts, the street ceiling applies. No extension makes a house worth more than the best house on the road, so the return is smallest where the house is already among the largest. And the work must be certificated — building control sign-off is what a surveyor and a buyer's solicitor will look for, and its absence costs more at sale than the certificate ever cost to obtain.
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