Single Storey Extension Cost and Design Ideas in the UK for 2025-26

As property prices rise and outdoor space becomes increasingly scarce, UK homeowners are rethinking how to expand their living space rather than relocate. The most feasible and practical solution is single storey extension. It is a smart, stylish, and practical solution that delivers the space you need without the complexity of multiple floors. But how much does a single storey extension cost in the UK?

Whether it’s a kitchen, rear, or side extension, a single-storey build offers flexible, value-adding design options.
This guide covers 2025–26 single storey extension costs, creative design ideas, and key planning tips for confident home improvement.

How Much Does a Single Storey Extension Cost in the UK

Average House Extension Costs in the UK

One of the biggest questions homeowners ask is, “How much does an extension cost in the UK?”

On average, house extension costs range from £20,000 to over £100,000, depending on the type, size, and finish. Most single-storey builds cost £1,500–£2,500 per m², with London projects pricier due to labour and material costs.

Key cost factors include:

Size and complexity: Larger, bespoke designs raise costs.
Materials: Premium cladding, glass roofs, or high-spec finishes add to the budget.
Location: Urban projects (especially in London or the South East) cost more.
Planning & design fees: Expect to allocate 8–12% of your total budget.

Typically, a small single storey rear extension might cost £30,000–£50,000, while larger or custom builds can exceed £70,000.

Single Storey Extension Costs Explained

A single storey extension remains one of the most affordable and versatile ways to add space. Whether extending your kitchen, adding a family room, or office, it lets you redesign your layout efficiently.

How much does a single storey extension cost in the UK:

Type of Extension	Estimated Cost Range	Average Cost per m²
Basic single storey	£20,000 – £40,000	£1,500 – £2,000
Mid-range design	£40,000 – £60,000	£2,000 – £2,500
Premium custom build	£60,000 – £90,000+	£2,500 – £3,000+

Keep in mind additional expenses for:

Architectural drawings and planning applications
Structural engineer fees
Utility connections
Finishes and landscaping

If you’re opting for high-end materials like aluminium bifolds or underfloor heating, factor in an extra 10–20%.

Inspirational Single Storey Extension Ideas

A single storey doesn’t mean single-minded design. Here are some modern ideas to make your extension both functional and stunning:

1. Rear Extensions

Perfect for open-plan living, rear extensions merge your kitchen, dining, and garden into one seamless space. Add bi-fold or sliding glass doors for natural light and garden views — a timeless design that feels bigger and brighter.

2. Side Return Extensions

Ideal for narrow London-style homes, a side return extension transforms unused alley space into a valuable living area. It’s a clever way to extend your kitchen or create a cosy lounge.

3. Wraparound Extensions

Combine rear and side extensions for a wraparound design that maximises space. This is a premium option but can revolutionise your floor plan.

4. Contemporary Finishes

Try skylights, exposed beams, and industrial glass walls for a modern aesthetic. A mix of brick and timber cladding adds warmth and character.

5. Sustainable Touches

Eco-friendly builds using recycled materials, green roofs, or solar panels not only reduce costs long-term but boost your home’s EPC rating.

Kitchen Extensions: Design and Budget Tips

A kitchen extension is one of the most popular single storey projects in the UK. It creates an open, sociable heart of the home — ideal for cooking, dining, and entertaining.

Typical Kitchen Extension Costs:

Standard finish: £20,000 – £35,000
Premium bespoke: £40,000 – £55,000
Luxury designer: £60,000+

Smart design ideas:

Add a central island for casual dining.
Use roof lanterns or skylights to bring in natural light.
Install sliding glass doors to blend indoors and outdoors.

While costs vary, a kitchen extension often delivers an excellent return on investment — improving lifestyle and property value simultaneously.

FAQs

Here are the answers to the most searched cost-related questions for extensions in the UK:

How much does a single storey extension cost?
Typically between £20,000 and £60,000, depending on size and finish.
What is the cost per square metre?
Average £1,500 – £2,500/m² (higher in London or for bespoke designs).
Rear vs. side extension cost?
Rear extensions are generally cheaper; side returns often require more structure.
Do kitchen extensions cost more?
Yes — due to plumbing, ventilation, and fitted units, expect a 10–20% uplift.

By knowing these benchmarks, you can plan your budget realistically and avoid costly surprises.

Additional Extension Considerations

Before finalising your design, consider:

Planning permission: Most single storey extensions fall under permitted development, but check if your home is listed or in a conservation area.
Building regulations: Required for structural safety, insulation, and drainage.
Professional fees: Architects, engineers, and surveyors typically add 10–15% of total cost.
Energy efficiency: Consider insulation and glazing upgrades to future-proof your investment.

If planning a future double-storey upgrade, expect conversion costs about 60–70% higher than the original build.

Conclusion

A single storey extension is one of the smartest investments for UK homeowners in 2025-26. It’s cost-effective, flexible, and enhances both comfort and value.

Before you begin, ensure you:

Get at least three quotes from reputable builders.
Consult an architect or planning consultant.
Review planning and building regulations for your area.

At Greenway Associates, we specialise in helping homeowners design and plan seamless extensions — from concept to planning approval.

👉 Book a free consultation today to discuss your single storey extension ideas and get expert cost guidance.