Two-storey extension cost UK 2026
Two-storey extensions cost £1,800–£3,200/m² fitted across both floors. A 30m² total (15m² ground + 15m² first floor) lands £55,000–£100,000+. Better value per m² than single-storey because foundations and roof are shared.
Cost guide ranges by total size
| Total area | Standard | Premium | Luxury |
|---|---|---|---|
| 20m² (10+10) | £35,000–£55,000 | £50,000–£75,000 | £70,000–£100,000 |
| 30m² (15+15) | £55,000–£85,000 | £75,000–£115,000 | £100,000–£150,000 |
| 40m² (20+20) | £72,000–£115,000 | £100,000–£150,000 | £140,000–£200,000 |
| 50m² (25+25) | £90,000–£140,000 | £125,000–£185,000 | £170,000–£250,000+ |
What's typically included
- Foundations (deeper than single-storey to support the load)
- Cavity walls in brick or block + render
- Suspended floor or beam-and-block first floor structure
- Pitched roof with tiles, fascias, soffits, gutters
- Standard windows and external doors
- First fix electrics and plumbing for both floors
- Plaster, decoration, basic flooring
- Building regs and structural calcs
- Stair (if connecting to new first floor) — usually £1,500–£3,500
What's typically NOT included
- Bathrooms (if first floor has en-suite or main bath: add £4,000–£15,000)
- Kitchen if ground floor is a kitchen extension
- Bedroom built-ins / wardrobes
- Bi-fold doors / roof lanterns (premium glazing)
- Loft conversion done in same project (often offered as bundle but separately costed)
- Planning application fees + architect drawings (£800–£3,500)
- Party wall agreement if needed (£700–£1,500)
Why per-m² is lower than single-storey
The expensive parts of an extension — foundations, roof, scaffolding, design fees, planning, building control — are largely fixed cost per project, not per m². Adding a second storey roughly doubles the floor area but only adds 60–70% to the cost. So the per-m² rate drops as the extension grows vertically.
This is why most architects recommend going two-storey if you have the budget headroom — it's the most cost-efficient way to add usable floor space.
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What drives the price
- Footprint vs height — wider extensions need more roof, more foundation perimeter; taller (3-storey) need more scaffolding and party wall complexity
- Number of bathrooms upstairs — each adds £4,000–£15,000 fully fitted
- Bedroom finish quality — built-ins, en-suites, dressing rooms add 25–50% to the upper floor
- Roof complexity — gable end, hip end, dormer all change cost; mansard adds significantly
- Glazing percentage — large rear-facing glazing on ground floor (bi-folds, sliding) adds £5,000–£15,000+
How we estimated these ranges
This is a guide only. The ranges below are intended for early budgeting and trade benchmarking. They are not a substitute for a site visit or an itemised quote from a qualified tradesperson. Always get a site-specific quote before agreeing work.
What's included in these ranges: typical labour costs, common materials at standard specification, and routine preparation or installation work for a standard project of this type.
What's excluded: unusual access (multi-storey, restricted parking), unforeseen structural issues, specialist design or architect fees, planning and building control application fees, premium or high-end finishes, emergency or out-of-hours work, and regional extremes.
Regional note: London, the South East and remote rural areas can vary significantly from the UK averages shown. London labour rates in particular can run 30–50% higher than national averages on the same scope.
Sources and checks used: publicly available UK trade supplier pricing (2025–2026), common day-rate and labour-duration assumptions used in trade quoting, internal example quote structures from TailoredQuote platform data, and where relevant cross-referenced regional contractor surveys and BCIS-style construction cost data.
Last reviewed: May 2026 by TailoredQuote. Prices in this guide will be reviewed and updated periodically.
Frequently asked questions
£1,800–£3,200 across both floors.
Yes — per m² cost drops 15–25% because foundations + roof are shared.
Usually yes — exceeds permitted development in most cases.
16–26 weeks typically.
Related cost guides
Last reviewed: May 2026
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