The Real Cost of Expanding Your Living Space: A Comprehensive Guide to House Extensions

Expanding your living space through a house extension can be one of the most impactful ways to increase your home’s value while adding much-needed space. Whether you’re considering an extra bedroom, a home office, or an expansive kitchen, an extension is a practical alternative to moving—saving you the time, stress, and financial burden of relocating.

But how much does a house extension really cost? Let’s explore the factors that contribute to the overall price and the value you can gain from extending your home.

Average House Extension Costs in the UK

House extension costs can vary significantly depending on location, materials, and the type of extension. On average, expect to pay between £1,350 and £3,000 per square metre. The cost can rise in areas with higher living expenses, such as London and the South East, where the upper range of prices exceeds £5,000 per square metre.

Here are some typical extension sizes and their estimated costs:

• Small extension (15m²): £20,000 - £45,000
• Medium extension (25m²): £30,000 - £75,000
• Large extension (35m²): £44,000 - £108,500
• Extra-large extension (two-storey, 60m²): Over £180,000

For most homes in the UK, budgeting around £2,000 per square metre is a good rule of thumb.

Cost Breakdown of Different Types of Extensions

Extension Type	Cost Per m² (Standard)	Cost Per m² (High-End)
Rear or Single-storey	£1,250 - £1,800	£1,750 - £3,000
Side Return or Wrap Around	£1,350 - £1,900	£1,850 - £3,000
Double/ Second-Storey	£1,350 - £1,900	£1,750 - £3,000

Cost of Common Extension Sizes:

• Small (15m²): Standard: £18,750 - £27,000, High-End: £26,250 - £45,000
• Medium (25m²): Standard: £31,250 - £45,000, High-End: £43,750 - £75,000
• Large (35m²): Standard: £43,750 - £66,500, High-End: £61,250 - £108,500

Factors Affecting the Cost of a House Extension

Several factors can influence the overall cost of your house extension. Understanding these elements will help you plan and budget more effectively.

1. Type of Extension

• Rear Extensions: These are the most straightforward and typically the least expensive. Extending at the back of the house is often simpler and more affordable than other options.
• Side Return Extensions: Great for utilising unused side space, but they are generally more expensive due to additional structural work.
• Wrap-Around Extensions: Combining rear and side extensions gives you more space but comes at a higher cost due to increased complexity.
• Double-Storey Extensions: While these can offer significant space, the additional labour and materials drive the overall cost higher than single-storey extensions.

2. Number of Storeys

• Single-Storey: Less expensive and easier to construct.
• Double-Storey: A cost-effective way to add significant space, but requires careful planning and more resources.

3. Size of the Extension

Larger extensions will naturally cost more, but you might benefit from a lower cost per square metre as the size increases.

4. Build Quality

High-quality materials such as premium windows, doors, and insulation will increase costs upfront, but could offer savings in terms of energy efficiency in the long run.

5. Additional Interior Design Costs and Fittings

Bespoke design features like custom cabinetry, high-quality flooring, or lighting can quickly escalate the cost of your project.

6. Roof Type and Material

• Flat Roofs: Cheaper to construct but may need more maintenance over time.
• Pitched Roofs: More expensive but better for drainage and long-term durability.

7. Added Features

Kitchens, bathrooms, and even walk-in wardrobes can significantly increase the cost of an extension. A high-end kitchen could range from £8,000 to £50,000, depending on the finishes and appliances.

8. Access

The ease or difficulty of accessing the site can impact costs. If machinery and materials need to be craned into place, expect higher expenses.

9. Location

Extensions in London and the South East will be more expensive due to the higher cost of living and labour.

10. Bespoke Ideas or Features

Custom designs and unique architectural features will add to your final bill. However, these features can make your extension stand out and boost your home’s overall value.

Admin and Planning Costs You’ll Need to Factor In

Before starting an extension, several administrative and legal costs must be considered. These can vary depending on your project’s complexity and location.

1. Architect Fees

Typically around 7% of construction costs. More intricate designs may increase this percentage.

2. Plans and Drawings

These are essential for ensuring your extension meets local planning laws. Services like Fast Plans can bundle this with site surveys, architectural drawings, and engineer calculations for a cost-effective solution.

3. Planning Permission

Costs around £238 in England. Check whether your extension qualifies for Permitted Development, which could save you this fee.

4. Party Wall Agreements

If your extension impacts a shared wall, you’ll need a Party Wall Agreement, which can add additional costs.

5. Lawful Development Certificate

Costs £108 and proves your extension complies with planning rules.

6. Home Insurance During Construction

You’ll need to extend your home insurance to cover construction. The cost varies depending on the project’s complexity and duration. From personal experience creating a large rear extension, insurance costs £650 per year.

Design and Planning Costs

The design and planning stages involve several important steps:

• Site Surveys: Assess your property to determine what’s possible.
• Architectural Drawings: Outlines the scope of the extension.
• Engineering Calculations: Ensures structural integrity.

These steps are crucial for a successful build and compliance with local planning regulations.

Typical Extra Costs for Special Features

Feature	Standard Cost	High-End Cost
Bathroom	£2,500 - £5,000	£4,000 - £15,000
Kitchen	£8,000 - £25,000	£12,000 - £50,000
Bifolding Doors	£3,000 - £8,000	£5,000 - £12,000
Walk-in Wardrobe	£750 - £1,500	£1,500 - £3,000

How Extensions Add Value to Your Home

House extensions offer a significant return on investment (ROI), potentially increasing your home’s value by up to 20%. On average, homeowners can expect an ROI of around 70%. When weighing the cost of adding space versus moving to a larger property, an extension may be the more economical choice.

Why Extensions Make Sense

• Avoid the expense and stress of moving.
• Increase your home’s value and space.
• Customise your living space to your exact needs.
• Stay in your preferred location.

Tips for Keeping Costs Under Control

1. Set a Realistic Budget: Be prepared to adjust for unexpected costs.
2. Prioritise Key Features: Decide on what you must have versus optional extras.
3. Get Multiple Quotes: Comparing contractors helps avoid overpaying.
4. Consider Phasing: If necessary, split the project into phases to spread out the costs.
5. Plan for Contingencies: Add a 10-15% buffer for any unforeseen issues.

Final Thoughts

Adding an extension to your home is one of the best ways to increase living space without the upheaval of moving. While the cost can range from £20,000 to over £100,000, thoughtful planning, budgeting, and design choices can make your dream extension a reality. Not only can it enhance your day-to-day living, but it can also significantly boost your property’s value in the long term.

At Dezigne, we're here to guide you through every step of your extension journey. Whether you need advice to make an informed decision or support in managing the entire project, we're just a call away—ready to help you create the space you’ve always envisioned.

Please note: All prices provided are estimates as of Summer 2024. Actual costs may vary based on individual project requirements, materials, and location-specific factors.