How Much Does a House Extension Cost?
£25,000 – £100,000
depending on size
House extensions cost between £25,000 and £100,000 depending on the size, type, specification, and location. A small single-storey extension is at the lower end; a large double-storey side or rear extension with premium finishes can exceed six figures. Professional fees for architects, structural engineers, and building control add a further £3,000-£10,000.
Average cost
£25,000 – £100,000
depending on size
Prices vary by region, property type and tradesperson. Always get at least two quotes.
What affects the price?
Type and size - a single-storey rear extension is cheapest per m2; a two-storey extension costs more in structural terms but less per m2 of added space
Specification - standard plastered walls and basic kitchen vs bifold doors, structural glazing, and underfloor heating
Location - London and the South East typically cost 20-40% more than the national average
Planning and professional fees - architects, structural engineers, and planning applications add £3,000-£10,000 depending on complexity
Labour vs materials
Build costs for extensions typically run at £1,800-£2,500 per m2 of new floor space, with labour representing around 40-50% of this figure. Projects take 12-24 weeks depending on scale.
Questions to ask your tradesperson
Ready to get it sorted?
Find available local builders near you — see who is free before you call.
Find a Builder — Free