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Cost GuidesUpdated May 2026By TradeMatch Editorial Team·28 November 2025·Updated 12 April 2026·8 min read
How Much Does a House Extension Cost? UK 2026 Prices
A house extension is one of the most popular ways to add space and value. But costs vary hugely depending on size, type and specification. Here is a comprehensive guide.
Extension Costs by Type
| Extension Type | Cost per m2 | 20m2 Extension |
|---|---|---|
| Single-storey rear | £1,500–£2,500 | £30,000–£50,000 |
| Single-storey side return | £1,800–£3,000 | £36,000–£60,000 |
| Double-storey | £1,200–£2,000 | £48,000–£80,000 |
| Wrap-around | £1,500–£2,500 | £45,000–£75,000 |
| Over-garage | £1,200–£1,800 | £24,000–£36,000 |
| Conservatory | £800–£1,500 | £16,000–£30,000 |
Note: Double-storey extensions cost 50–70% more than single-storey but give you twice the space, making them better value per m2.
Hidden Costs to Budget For
Architect/designer: £2,000–£5,000 for plans. Planning application: £206 (England). Building regulations: £500–£1,000. Structural engineer: £500–£1,500. Party wall surveyor: £800–£1,500 per neighbour. Temporary kitchen/bathroom: If extending your kitchen, budget for a temporary setup. Landscaping: Making good the garden after construction.
Planning Permission
Many single-storey rear extensions fall under Permitted Development rights (up to 3m for attached houses, 4m for detached). Larger extensions, side extensions, and two-storey extensions usually require full planning permission. Always check with your local planning authority before starting work.
Frequently Asked Questions
How long does a house extension take?
A single-storey extension typically takes 10–16 weeks from groundworks to completion. A double-storey extension takes 14–20 weeks. Weather, planning delays and supply issues can extend timelines.
Do extensions add value?
Yes. A well-designed single-storey extension can add 5–10% to property value. A double-storey extension can add 10–20%. The return on investment depends on your area — in high-value locations, extensions almost always pay for themselves.
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