Costs & Budgeting
Is £30,000 enough for an extension?
What that budget realistically stretches to, and where it goes further.
It depends heavily on size and specification. Published UK ranges put a single-storey extension at roughly £1,800-£3,000 per m², which puts a very small, simply-specified extension within reach of a £30,000 budget but a typical 20-30m² kitchen-diner extension well above it. That budget often stretches further on a garage conversion or a smaller garden room, where there's no new footprint to build.
Last updated 20 August 2026
What £30,000 buys in a new-footprint extension
At the published general UK rate, £30,000 covers somewhere in the region of 10-16m² of new-build extension before fittings and finishes are accounted for - a small addition rather than a full kitchen-diner. Costs run higher in London and the South East, and can run lower on a very simple, small structure with a basic specification.
Where the same budget goes further
Projects that don't need a new foundation, roof and structural shell - a garage conversion, a basement or cellar conversion using existing space, or a smaller garden room - generally cost less than an equivalent new-footprint extension, because a large part of what you're paying for in an extension is the shell itself.
What actually moves the figure
Size is the biggest lever, but specification (kitchen fittings, glazing, flooring) and site-specific factors (access, ground conditions, whether services need extending) all move the final cost within any given size. See our guide to what affects the cost of a building project for the full list.
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