How Much Does a Single Storey Extension Cost in 2026? in Weymouth
A single-storey rear extension is the most popular home improvement in the UK. The headline build cost is £1,800–£2,800 per m², but the total project cost is always higher once you factor in professional fees, kitchen, landscaping, and the hidden costs nobody warns you about. Here is what Weymouth homeowners should expect to pay.
Local cost range — Weymouth
£1,700–£2,500/m²
What affects costs in Weymouth
Weymouth offers some of the most affordable build rates in the area. Seafront properties are the exception — salt air exposure requires marine-grade materials.
Cost estimator
Rates for Weymouth
6m × 4m = 24m²
Estimated cost in Weymouth
Excl. VAT (£9821 – £14720)
Local insight: Weymouth offers some of the most affordable build rates in the area. Seafront properties are the exception — salt air exposure requires marine-grade materials.
Cost breakdown
Build cost per square metre (2026)
The build cost covers foundations, walls, roof, windows, doors, plastering, electrics, plumbing, and basic decoration. In 2026, expect to pay: £1,800–£2,200/m² for a standard specification, £2,200–£2,800/m² for a high specification, and £2,800–£3,500/m² for premium finishes. These are Dorset figures — London and the South East run 15–25% higher.
What the build cost does NOT include
The kitchen (£8,000–£25,000), flooring (£1,500–£5,000), landscaping to make good the garden (£2,000–£8,000), decoration beyond basic emulsion, and any furniture or fittings. These 'extras' typically add 25–40% on top of the build cost.
Professional fees breakdown
Design: £250 (PlanBuildCo) vs £3,000–£10,000 (traditional architect). 3D laser scan: £650. Structural calculations: £350. Certificate of Lawfulness: £1,500. Planning application (if needed): £2,200 + £258 council fee. Building Regulations drawings: £399. Total professional fees: £2,000–£5,000 with PlanBuildCo.
The hidden costs
Party wall agreements (£700–£1,500 per neighbour), building control fees (£400–£800), skip hire (£300–£500 per skip), scaffolding (£500–£1,500), temporary facilities if your kitchen is out of action, and increased insurance premium during building works. Budget an additional £3,000–£8,000 for these.
How to budget realistically
Take the build cost, add professional fees, add kitchen and flooring, add hidden costs, and add 15% contingency. For a typical 4m × 6m (24m²) extension: build £43,000–£67,000 + kitchen £12,000 + fees £3,000 + hidden £5,000 + contingency £9,000 = £72,000–£96,000 all-in.
| Extension Size | Build Cost | Estimated Total (all-in) |
|---|---|---|
| 3m × 4m (12m²) | £22,000–£34,000 | £40,000–£55,000 |
| 4m × 5m (20m²) | £36,000–£56,000 | £55,000–£80,000 |
| 4m × 6m (24m²) | £43,000–£67,000 | £65,000–£95,000 |
| 6m × 6m (36m²) | £65,000–£100,000 | £90,000–£140,000 |
| 8m × 5m (40m²) | £72,000–£112,000 | £100,000–£155,000 |
National guide figures. Local rates in Weymouth: £1,700–£2,500/m².
Frequently asked questions
National guide
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