Adding on to your house in London may be fun, but a lot of homeowners have trouble figuring out how much London extension cost. If you’re thinking of a single-storey or double-storey expansion in London, knowing the cost variables ahead of time can save you time and money and save you from going over budget.

At Studio 20 Architects, we assist London homeowners in designing elegant, practical, and affordable additions. With proper planning, you may add room and value to your house over time.

“According to a 2025 guide on extension costs for London, a single-storey extension typically costs between £2,200–£3,300 per m² (excluding VAT).”

Key Takeaways

• A​‍​‌‍​‍‌​‍​‌‍​‍‌ practical comprehension of how much the London extension will cost is one of the ways to prevent money surprises.
• Single-storey extensions are cheaper, while double-storey extensions provide higher value over a longer period.
• Per m2 pricing changes depending on the materials, the quality of the finishes, the labour and the regulations that need to be complied with.
• Architects make the process faster, less wasteful and more efficient in terms of controlling the spending of the project.
• Invisible costs such as the installation of utilities, the preparation of the land, and the interior finishing should be accounted for from the very beginning.
• Being wise with the budget, the choice of materials and having a clear plan are the main things that will guarantee a building process without any ​‍​‌‍​‍‌​‍​‌‍​‍‌problems.

What Factors Affect the Cost of a Single Storey Extension in London?

A single-story addition is a common alternative for homeowners who want to add more living space without taking up too much room in the yard. The ultimate final single storey extension pricing will depend on its size, design, materials, and any rules that must be followed.

Things to remember:

• The average single storey extension London cost between £1,200 and £2,200 per square meter.
• A simpler design makes structures less complicated and lowers the cost overall.
• Early engagement with London architects ensures that space is used well.

How Much More Will a Double Storey Extension Cost Compared to Single Storey?

Adding a double storey extension provides you with more room without taking away from your yard, but it costs more. These projects are harder than single-story ones because they need extra plumbing, structural reinforcements, and stairs.

Things to think about:

• A double-story expansion will cost between £1,800 and £3,000 per m2.
• Planning ahead with architects in London saves money on redesigns.
• Two-story additions usually add greater value to a home when it is sold than one-story additions.

How​‍​‌‍​‍‌​‍​‌‍​‍‌ to figure out the house extension cost per m2 London?

Determining the house extension cost per m2 London enables you to set up your budget in a more practical way. Basically, it is about taking the area that you are going to enlarge, multiplying it by the average prices, and then sprinkling some more money for the finishes, fixtures, and the fees of the professionals.

• Allow 10 to 15 per cent more of your budget for unexpected costs.
• Consult architect experts to be sure you know the cost of a single-storey or double-storey extension.
• Including the costs of the local authority, VAT, and the design from the very ​‍​‌‍​‍‌​‍​‌‍​‍‌beginning.

 

Can Hiring Architects in London Help Reduce Extension Costs?

If you work with professional architects in London, you won’t have to pay for anything you don’t need, and the design will be efficient. Architects can help you with planning permission applications, come up with feasible plans, and propose materials that won’t break the bank.

• Getting involved early lowers the costs of redesigning and fixing structural problems.
• Architects may suggest design options that save money without changing the look.
• Phased building planning makes it easier to keep track of money.

What Hidden Costs Could Increase Your London Extension Budget?

Even a well-planned project may have hidden expenditures that raise the London extension cost. These costs include preparing the land for difficult terrain, moving utilities, finishing the inside, and paying for legal or planning expenses.

Tips to avoid surprises:

• Before you finish your designs, do a professional survey.
• Ask London architects for detailed estimates.
• Put off fancy finishes until later if you need to, and focus on the most important changes first.

How Can You Save Money on London Extensions Without Sacrificing Quality?

Budgeting​‍​‌‍​‍‌​‍​‌‍​‍‌ intelligently gives homeowners the opportunity to save money while still maintaining quality and good design. Homeowners can easily cut down on their expenses by selecting standardised materials, not making drastic changes to the structure, and planning their work for the off-peak seasons.

Some suggestions to help you decide:

• If you don’t really need the vertical space, then just go for a single storey extension London cost.
• Talk over the changes in the design with the architects in London in order to have efficient layouts.
• Pay for the energy-efficient fixtures now to be able to save on the operating costs ​‍​‌‍​‍‌​‍​‌‍​‍‌later.

Why Investing in a London Extension Adds Long-Term Value

A well-planned addition not only gives you more room to live in, but it also makes your house worth more when you sell it. Single-story and double-story expansions both make your house more useful, more attractive, and more contemporary.

Tips for getting the most value:

• Make sure the expansion fits in perfectly with the current structure.
• Pay attention to areas that are in great demand, such as kitchens and living rooms.
• Work with Studio 20 Architects to come up with ideas that fit your lifestyle and will sell.

Make Your London Extension Project Stress-Free and Affordable

Understanding the London extension cost and dealing with the pros from the outset will make the process go more smoothly. Studio 20 Architects will help you design a single-storey extension or double-storey extension so that you stay within your budget, prevent delays, and make a room that makes your house more useful and valuable.

FAQs

What​‍​‌‍​‍‌​‍​‌‍​‍‌ is the average cost of a small single storey extension in London?

London small single-storey extensions usually cost from £25,000 to £45,000, with the price being influenced by the size, layout, materials used, and the location of the flat.

Is a double storey extension cheaper than building two separate floors later?

Yes. It is more cost-effective to build a double-storey extension at once than to carry out one floor now and another later, as the foundations and roofing can be done at the same time.

How long does a home extension usually take in London?

Most single-storey extensions take 10 to 14 weeks, while double-storey extensions may take anywhere from 14 to 20 weeks, the time being dependent on the complexity of the design and permissions.

Do I need planning permission for every extension in London?

No, not always. Most extensions are permitted developments; however, factors such as size, location, and design can determine if planning permission is necessary.

Are architects necessary for smaller extensions?

Yes. Even the tiniest extensions benefit from architectural planning, accurate drawings, and compliance checks, thus helping to avoid financially costly structural ​‍​‌‍​‍‌​‍​‌‍​‍‌mistakes.