How Much Does a House Extension Cost in 2025? A Complete UK Guide
House extensions are one of the most popular home improvement projects in the UK, adding significant living space and increasing property value by 20-30%.
A single-storey rear extension (20m²) typically costs between £30,000 and £50,000. A double-storey extension (40m²) ranges from £60,000 to £100,000. Wrap-around extensions cost between £80,000 and £150,000.
Labour typically accounts for 40-50% of the total cost, with materials making up 30-40%. Additional costs include planning permission fees (£206), building control charges (£200-£500), structural engineer reports (£500-£1,000), and architectural drawings (£1,000-£3,000).
Always get at least 3 detailed, itemised quotes from verified contractors. The cheapest quote is rarely the best value — focus on the contractor’s reputation, reviews, and the detail in their quote.
Frequently Asked Questions
How much does a 20m² extension cost?
A single-storey 20m² rear extension typically costs £30,000 to £50,000 including labour and materials.
Do I need planning permission for an extension?
Many extensions fall under permitted development rights. Single-storey rear extensions can extend up to 4m beyond the rear wall for detached houses, or 3m for other houses, without planning permission.
How long does a house extension take?
Most single-storey extensions take 8-12 weeks. Double-storey extensions take 12-16 weeks from start to finish.
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