Quick summary: double storey extension costs
In the UK, double storey extension costs typically start from around £60,000–£70,000 for a modest rear addition and can rise to £120,000 or more for larger, more complex designs — especially wrap-around or multi-room extensions in high-cost areas.
- Small 2-storey rear extensions: usually £65,000–£85,000 including VAT and basic finishes.
- Wrap-around or side-return double storey builds: from £85,000–£120,000+ depending on layout and access.
- Per square metre: typical guide range is £1,800–£2,800/m² (build cost only – excluding design, planning and fees).
- Additional costs apply for planning drawings, structural design, Building Control, kitchen/bathroom fit-outs and finishes.
The cost of your double storey extension depends heavily on its size, location, design complexity and the level of finish you’re aiming for. This guide will help you understand what to expect — and what’s realistic — before you speak to builders or architects.
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Typical double storey extension costs (UK 2025)
The average double storey extension cost in the UK currently sits between £1,800 and £2,800 per square metre. A small two-storey rear extension (around 30–35m² total) might start from £65,000–£75,000 including VAT and basic finishes. Larger wrap-arounds or multi-room builds can easily reach £120,000+.
- Typical range: £1,800–£2,800 per m² (build cost only)
- Two-storey rear extension (basic): £65,000–£85,000
- Wrap-around or large double: £85,000–£120,000+
What drives double storey extension costs?
1. Size and shape
A larger footprint means more materials, longer build times and more internal work. Even a second storey adds relatively less cost per m² than the ground floor — but only if the footprint stays efficient.
2. Roof complexity
A double hipped roof, dormers or roof windows will cost more than a basic gable or flat roof. Structural steelwork also adds cost, particularly on wrap-around extensions.
3. Internal layout and fit-out
Including a bathroom, utility or kitchen in the upstairs layout? These require extra plumbing, drainage and finish costs. The more rooms you divide the space into, the higher the cost per m² usually becomes.
4. Access and logistics
Urban sites, tight plots or rear-only access can make material delivery harder — and increase labour costs. Builders may need temporary scaffolding, hoists or out-of-hours work.
5. Location in the UK
Labour and materials are significantly more expensive in London and the South East than in the Midlands or North. Quotes will vary widely across regions.
Double vs single storey extension: cost per m²
It’s tempting to assume that a double storey extension costs twice as much as a single one. In reality, adding the second storey often works out cheaper per m².
- Single storey extension: £2,000–£3,000 per m² (higher due to roof, groundwork, etc.)
- Double storey extension: £1,800–£2,800 per m² (spreads structural cost across two floors)
So if your project makes sense spatially, the second floor can offer better value — especially if you need extra bedrooms or bathrooms.
For a full breakdown of single-storey options, see our guide to single storey extension costs.
Wrap-around double storey extension costs
Wrap-around extensions — those that extend to the rear and side — are among the most expensive two-storey designs. That’s because they usually require more:
- structural support (steel beams, load redistribution)
- roof redesign or rebuild
- internal changes to existing rooms and staircases
- external walls, party wall agreements and drainage works
Expect to pay from £90,000–£130,000+ for a full wrap-around double storey extension, depending on location and internal fit-out.
Budgeting for drawings, approvals and extras
In addition to build costs, you’ll need to budget for:
- Planning drawings – typically £800–£1,500
- Building Regulations drawings – another £800–£1,500
- Structural calculations – around £400–£1,000 depending on complexity
- Planning application fees – around £258 in England
- Building Control fees – varies by authority or Approved Inspector
Want to sense-check your double storey plans and quote?
Our team can review your plans and tell you if the layout, costs and permissions make sense — before you commit.
FAQs: double storey extension costs
What is the average cost of a double storey extension in the UK?
Most two-storey extensions cost between £1,800 and £2,800 per square metre in 2025. That means a 35m² extension might cost around £70,000–£95,000 depending on layout and spec.
How much does a wrap-around double storey extension cost?
Wrap-around extensions tend to be larger and more structurally complex. Costs often range from £90,000 to £130,000+. These figures don’t include drawings or planning fees.
Is it cheaper per m² to build a double storey extension?
Yes — while the total cost is higher, double storey builds are usually more cost-efficient per m² than single storey extensions, as you reuse foundations and roofing elements.
Do I need planning permission for a double storey extension?
In most cases, yes. Some rear double storey extensions can be done under Permitted Development if they meet strict limits. Use our planning permission checker to find out.
How can I reduce my double storey extension cost?
Use a simple shape, limit plumbing-heavy rooms, stick to standard sizes and plan the build outside peak season. Getting multiple quotes and clear drawings also helps control costs.
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Send us what you’ve received — we’ll help spot missing items or unexpected extras.
- Typical cost range (UK 2025) £65,000–£120,000+ depending on size and spec
- Per square metre guide £1,800–£2,800/m² (build cost only)
- Planning & design extras £2,000–£3,000 typically for drawings, applications and approvals
- Cost-effective layouts Simple rectangular footprints with stacked rooms are most efficient
- Key driver of cost Roof complexity, plumbing, and structure (steels, foundations)
- Planning permission Usually required — use our guide to check: Do I Need Planning Permission?
Official guidance
Next steps & useful guides
- Extension Costs – Complete Homeowner's Guide (UK)
- Making Plans – Complete Guide to Costs, Drawings & Approval
- Planning Permission Cost (UK): Complete Guide for Homeowners
- Planning Permission Drawings – What’s Included & Typical Costs
- Plans for Building Regulations – What You Need & When
- Structural Calculations – When You Need Them
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