Planning a two storey extension is an excellent way to increase your living space without moving, especially for growing families or those needing extra bedrooms, offices, or bathrooms. One of the most common questions homeowners ask is: how much does a 2 storey extension cost?
In this article, you’ll find:
- 2025 average cost for a 2 storey extension
- Cost examples based on size, quality, and type
- What affects pricing, from materials to location
- Comparison between single storey extension costs and double storey extension costs
- Planning permission rules and building regulations explained
- Tips to budget your project and avoid unexpected costs
- How to choose the right builder for a two storey extension
- How ArkiPlan can help you get accurate quotes with professional plans
By the end, you’ll understand the full picture—from cost breakdowns to smart budgeting strategies—so you can move forward with confidence.
Average Cost of a Two Storey Extension in the UK
The cost of a two storey extension depends on factors like size, design, materials, and location. Generally, the average cost of two storey extensions in the UK ranges from £2,400 to £3,200 per square metre.
For example, a 40m² double storey extension (20m² per floor) typically costs between £96,000 and £128,000.
| Build Quality | Cost per m² | Example (40m² Total) |
|---|---|---|
| Basic Build | £1,500 – £2,200 | £60,000 – £88,000 |
| Mid-Range Finish | £2,200 – £2,800 | £88,000 – £112,000 |
| High-End Specification | £2,800 – £3,500+ | £112,000 – £140,000+ |
Keep in mind that prices can be 10–20% higher in London and the South East due to higher labour and material costs.
What Influences the Cost of a Two Storey Extension?
The extension cost depends on several factors:
- Size and complexity: Larger footprints and more complex layouts increase cost.
- Materials and finishes: High-end fixtures, glazing, and insulation add to the price.
- Structural requirements: Reinforcing foundations and roofs for two floors.
- Location: Regional labour and material costs affect prices.
- Planning and regulations: Permits, structural engineering, and building control add time and expense.
If you’re considering a two storey side extension, note that these tend to have specific costs related to the footprint and integration with your existing structure, often falling between £100,000 and £140,000 depending on size and finish.
How Much for Two Storey Extension vs Single Storey?
Many homeowners wonder if a two storey extension is more expensive than a single storey one. The simple answer is: Yes, a two storey extension costs more overall because you’re adding an entire extra floor, but it’s actually more cost-effective when you consider the price per square metre.
For example, a 20m² single storey extension might cost between £36,000 and £50,000. This gives you extra ground floor space but no additional upstairs area.
On the other hand, a 40m² two storey extension (which has roughly 20m² on each floor) typically costs between £96,000 and £128,000. While this is a higher total cost, you’re essentially doubling your usable space for less than double the price.
This is because two storey extensions share structural elements like foundations and roofing across both floors, making them more efficient to build compared to two separate single-storey extensions. So, when looking at the cost per square metre, a two storey extension usually offers better value for money.
If you need additional bedrooms, a home office, or more living space upstairs without increasing your home’s footprint, investing in a two storey extension is often the smarter choice.
Do You Need Planning Permission for a Two Storey Extension?
Most two storey extensions require planning permission, especially if they increase the property’s height or footprint significantly. However, some may qualify under permitted development rights if they meet specific size and location criteria.
Building regulations approval is mandatory for safety and energy efficiency and applies to both single and two storey extensions.
Budgeting for a two storey extension requires careful planning to avoid unexpected costs. Here are some key steps to help you manage the cost of a double storey extension effectively:
- Start with detailed architectural drawings and plans tailored to your needs. This helps builders understand your project and provide accurate estimates.
- Work with builders who have experience in two storey side extensions, rear extensions, and other multi-storey projects.
- Always request clear, itemised quotes based on your specific design to compare prices and understand what’s included.
- Don’t forget to factor in additional costs like plumbing, heating, electrics, and high-quality finishes, which can impact the overall extension cost.
At Arkiplan, we specialise in delivering professional and customised plans for your double storey extension cost UK project, helping you get precise builder quotes and avoid costly surprises during construction.
Choosing the Right Builder for Your Two Storey Extension
Selecting the right builder is crucial to managing your two storey extension cost effectively. Look for a builder with a proven track record in delivering double storey extension projects on time and within budget. Experienced builders understand the complexities of double story extension costs and can help you avoid unexpected expenses.
Be sure to:
- Check references and review past projects similar to your planned two storey side extension or rear extension.
- Request detailed, itemised quotes to compare the cost of a double story extension fairly.
- Confirm that the builder fully understands your design goals, budget, and timeline to ensure smooth communication throughout the project.
By choosing the right builder, you protect your investment and increase the likelihood that your two storey extension will be completed on budget and to your satisfaction.
Final Thoughts
Deciding how much for a two storey extension depends on many factors, but understanding the average costs, planning requirements, and design choices will help you plan effectively.
Whether you want a side extension cost 2 storey or a large double story extension, investing in good design and choosing the right team will ensure your project is successful and offers excellent value.
If you’re wondering how much does a 2 story extension cost for your home, contact Arkiplan for expert, tailored advice and professional architectural plans to get your project started the right way.