Two-Storey Extension Costs & Planning Guide UK 2025

Two-Storey Extension Costs & Planning: A 2025 Guide for UK Homeowners

Why Consider a Two-Storey Extension?

Two-storey extensions are a powerful way to increase your living space and property value without doubling your footprint. Whether you’re creating extra bedrooms, expanding your kitchen-diner, or crafting a modern open-plan layout, these extensions provide substantial space at better value per square metre than single-storey alternatives.

Key benefits include:

More living space without losing garden area
Increased resale value of your home
Cost efficiencies in shared foundation and roof work

While the upfront investment is significant, the long-term lifestyle and financial gains can outweigh the initial outlay—especially in high-demand urban areas.

Book a free design consultation with Fourth Wall to explore your options.

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How Much Does a Two-Storey Extension Cost in 2025?

Two-storey extension costs in the UK range from £130,000 to £150,000+, depending on location, design complexity, and finish level.

Average Cost Per Square Metre:

Build Quality	New Build Areas	Refurbished Areas
Basic	£1,500/m²	£800/m²
High-Quality Standard	£1,650/m²	£875/m²
Premium	£1,800/m²	£950/m²

Additional Costs:

Architect Fees: £1,000 – £5,000 or 7–15% of build cost
Planning Application: ~£200
Measured Survey: £300 – £1,000
Building Regulations: £2,000 – £5,000
Party Wall Agreements: £700 – £1,500 (if applicable)
Project Management: 3–7% of build costs

Factors That Influence Extension Costs

Several variables affect your total spend, including:

Location: Labour and material prices vary across the UK
Extension Size & Design: Larger, bespoke designs cost more
Glazing Choices: Large sliding doors or full-height windows add both material and structural costs
Site Access: Difficult-to-access plots cost more in logistics
Professional Team: A full-service architectural practice offers peace of mind but comes at a premium

Hiring qualified experts may cost more upfront but often saves you time, stress, and errors in the long term.

Get a quote for design services today

Planning Permission for Two-Storey Extensions

Most two-storey extensions require planning permission. While some may fall under Permitted Development, the criteria are strict.

Permitted Development Criteria:

Must not extend beyond the rear wall by more than 3 metres
Must be at least 7 metres from the rear boundary
Roof pitch must match existing house
Side windows must be obscure-glazed and non-opening below 1.7m

You cannot use Permitted Development if:

Your home is in a conservation area, AONB, or National Park
You’re extending to the side with more than one storey
Your home has already reached the maximum volume of extension under PD rights

Learn more from Planning Portal UK.

Best Practice: Partnering with a qualified professional significantly increases your chance of approval on the first attempt.

Meeting UK Building Regulations for Two-Storey Extensions

Even if you don’t need planning permission, your build must comply with UK Building Regulations.

Building Regs cover:

Structural safety
Fire protection
Insulation and energy efficiency
Soundproofing and ventilation
Waste disposal and drainage
Glazing and electrical safety

Due to the complexity of two-storey extensions, you may need:

Structural engineer
Drainage consultant
Party wall surveyor

Need clarity? Speak to our team about building regulations.

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Single vs Two-Storey Extensions – What’s Right for You?

Feature	Single Storey	Two Storey
Cost	Lower	Higher
Planning Simplicity	Easier	Often requires approval
Disruption	Less invasive	May require relocation
Space Gained	Limited to ground floor	Significant on both floors
Value Boost	Moderate	High

If you’re budget-conscious or prefer minimal disruption, a single-storey extension may suffice. But for homeowners seeking long-term value and major spatial transformation, two-storey builds deliver far more return.

FAQ Section

How much does a two-storey extension cost in the UK?

In 2025, expect to spend £130,000–£150,000+ for a typical two-storey extension, depending on location, size, and specification.

Do I need planning permission for a two-storey extension?

Usually yes. While a few projects fall under Permitted Development, most require full planning approval due to their size and impact.

What factors most affect two-storey extension costs?

Costs are influenced by your location, build quality, project complexity, materials used, and professional team.

Is a two-storey extension worth the investment?

In most cases, yes. A well-designed two-storey extension can significantly boost your home’s usability and resale value—especially in high-demand markets.