In short: a two-storey (double) extension typically costs £2,000–£3,200 per square metre of floor area in 2026. Because the foundations and roof are shared across both floors, it is usually better value per m² than a single-storey extension. Adding 40m² over two floors is roughly £80,000–£128,000 for the build — before VAT, fees and fit-out. The South East sits at the higher end.
A two-storey extension is the big step up in space — often an extra reception room below and a bedroom or bathroom above. The total bill is higher than a single-storey, but the cost per square metre is usually lower. Here are current 2026 UK figures, why it works out better value, and what to budget for on top of the headline rate.
Cost by size (2026, standard build)
| Total floor area (two floors) | Standard spec (£2,000–£2,600/m²) | Higher spec / South East (£2,600–£3,200/m²) |
|---|---|---|
| 30 m² | £60,000–£78,000 | £78,000–£96,000 |
| 40 m² | £80,000–£104,000 | £104,000–£128,000 |
| 50 m² | £100,000–£130,000 | £130,000–£160,000 |
These are build-cost ranges before VAT and fees. Floor area here means the combined space across both storeys.
Why two-storey is better value per m²
The expensive parts of any extension — the foundations, the groundwork and the roof — are largely fixed costs. Build a single-storey extension and those costs are spread over one floor. Build up as well, and the same foundations and roof serve two floors, so the cost of the second storey is mostly walls, windows and internal finishes. That is why doubling the floor area does not double the price, and why a two-storey extension often gives the most space for the money if you need it.
What is included — and what is extra
A per-square-metre build figure covers foundations, the brick and block shell over two floors, the roof, standard windows and doors, first-floor structure and basic plastering. Budget separately for:
- VAT — normally 20% on a domestic extension.
- Professional fees — architect or designer, structural engineer and building control, commonly 10–15% of the build cost.
- Planning fee — a householder application in England is £528 from April 2026 (a two-storey extension is more likely to need one).
- Structural steel — larger openings and the extra floor often need steel beams.
- Party wall surveyor — likely if you build near or on a shared boundary.
- Fit-out — kitchen, bathroom, flooring, decorating and knocking through into the house.
Two-storey specific costs to expect
Compared with a single-storey, a two-storey extension adds a few things: foundations designed for the extra load, more scaffolding (you are working at height for longer), first-floor joists or beams, and matching the brickwork across two storeys so the new elevation reads as one with the house. Good brick matching matters more on a taller elevation because there is more of it on show.
Planning permission
Two-storey extensions are less likely to be permitted development than single-storey ones. There are limits on how far they project, how close they come to boundaries, and a 45-degree rule that protects neighbours' daylight. Some still go through as permitted development, but many need a householder planning application — so check before you design too far. The Planning Portal sets out the current rules.
Lead times to plan around
A two-storey project takes longer than a single-storey one:
- Design and drawings: 6–10 weeks.
- Planning decision: around 8 weeks from validation (longer in conservation areas or on listed buildings).
- Building regulations and structural design: 4–6 weeks.
- Construction: 16–28 weeks depending on size and finish.
From first idea to finished rooms, budget the best part of a year. Our guide on the order to do things and who to contact first walks through it.
Where the brickwork sits in the cost
The bricklaying is labour-only — you or your main contractor buy the bricks, blocks, sand and cement, and we lay them. See what a bricklayer charges for an extension for how that part is priced, and our single-storey extension cost guide if you are weighing the two.
Figures are 2026 UK market guides drawn from published cost data and our own experience; treat them as ballpark. Your real price depends on your site, spec and where you are.
Getting a price for your extension
Every extension is different, so the brickwork is priced after we have seen the job. If you are planning a two-storey extension in Hampshire, Berkshire or Surrey, see our extension work or send us the details and we will come and look.
Frequently asked questions
How much does a two-storey extension cost in the UK?
In 2026 a two-storey extension typically costs 2,000 to 3,200 pounds per square metre of floor area at standard specification. For example, adding 40 square metres over two floors is roughly 80,000 to 128,000 pounds for the build. London and the South East sit at the higher end. These figures usually exclude VAT, professional fees and interior fit-out.
Is a two-storey extension cheaper per m2 than single-storey?
Usually yes, per square metre. A two-storey extension roughly doubles the floor area for a much smaller increase in cost, because the foundations and roof are shared across both floors instead of being built twice. The total bill is higher than a single-storey, but each square metre tends to work out better value.
Do you need planning permission for a two-storey extension?
Often, yes. Two-storey extensions are less likely to fall under permitted development than single-storey ones, and there are limits on depth, height and how close they sit to boundaries, plus a 45-degree rule to protect neighbours' light. Some still qualify as permitted development, but many need a householder planning application, so it is worth checking early.
How much does a double extension cost for a 3-bed house?
It depends on size, but a typical two-storey side or rear extension adding around 30 to 50 square metres of floor space over two floors commonly falls between 70,000 and 130,000 pounds for the build in 2026, before VAT, fees and fit-out. A larger or higher-specification project, or one in the South East, can be more.
Does a two-storey extension need bigger foundations?
The foundations carry more load than a single-storey extension, so they are designed for the extra weight, but you are not paying for two separate sets of foundations. That shared groundwork and roof is exactly why a two-storey extension is usually better value per square metre. The foundation design is confirmed by a structural engineer and building control on site.
Do builders charge VAT on a two-storey extension?
Usually yes. Most extension quotes are shown before VAT, and you normally pay 20 percent VAT on labour and materials for a domestic extension. Always check whether a quote includes VAT before comparing prices, because on a two-storey project it is a large sum.