How Much Does A House Extension Cost?

As a UK homeowner, the prospect of a house extension can be both exciting and daunting. While expanding your living space can provide numerous benefits, understanding how much a house extension costs is crucial to ensure that your project remains within budget. In this guide, we’ll delve into the likely costs of a house extension, taking into account various factors that can influence the overall expenses. We are ideally placed to help because, thanks to our house extension services, we have years of practical hands-on experience to share.

Calculating the Cost Of A House Extension

Before diving into the costs, it’s essential to have a clear understanding of the goals and scope of your house extension project. Are you looking to add an extra bedroom, a larger kitchen, or perhaps a new living space? The type and size of your extension will clearly significantly impact overall house extension costs – moving from a cost-effective straightforward single-storey extension to a larger, high-end multi-storey project that could run into a significant spend.

Additionally, don’t hesitate to seek recommendations from friends, family, and neighbours who have had fitted kitchens recently. Personal experiences can offer valuable insights and help you avoid potential pitfalls.

Factors Affecting Home Extension Costs

Several factors contribute to the final cost of a house extension and they all need to be taken into account when calculating your budget. This is why we recommend getting professional help to make sure all the issues are covered before beginning your project. Realising you’ve forgotten something or uncovering a surprise will lead to the budget heading skyward.

Factors that will impact your house extensions costs include;

Size and Scope

Naturally, larger extensions will require more materials and labour, leading to higher costs. This is why house extension cost per m2 is typically used for initial calculations. The complexity of the design and the addition of amenities like bathrooms or intricate finishes can also increase expenses, but the bulk of your cost is based on size.

House Extension Cost

Location & Labour

The cost of construction can vary significantly across London and the South East. The closer you are to the Capital, generally the higher the budget you will require. Labour costs can vary based on location and demand. The availability of skilled tradespeople, such as builders, plumbers, electricians, and carpenters, will also contribute to a substantial portion of the overall cost.

Planning and Design

It is important to understand if your extension requires planning permission. Obtaining it and providing the required architectural drawings are essential steps in the process that come at a cost. These initial expenses need to be factored into your budgeting exercise. We recommend that you always talk to a professional because errors with planning approval can prove incredibly costly.

House extension calculator


The choice of materials, from your chosen foundations to your preferred roofing solution, can have a significant impact on house extension costs. Higher-quality or hard-to-come-by materials will increase the budget. That said, they can offer long-term savings through durability and a reduced need for maintenance. It is important to check that any house extension cost examples, therefore, consider a project’s whole lifecycle. Projects that initially seem expensive can be seen as more reasonable viewed over time.

Utilities and Infrastructure

Extending utilities such as electricity, plumbing, and heating to the new space can involve additional costs. This might include upgrading your existing systems to accommodate the extension. There might also be costs associated with new connections and increased usage of electricity and water for example.

Average Costs For Home Extensions

We have shared some average costs below. There are also many home extension cost calculators online that may give you an approximate figure for your plans. These are, however, only of limited use as all house extensions are unique. We recommend using published information on the internet strictly as an initial guide and, as soon as you are able, contact us for an initial, obligation-free accurate quote. We have, however, shared some illustrative average costs below.

Basic Single-Storey Extension

A straightforward, single-storey extension, such as a rear kitchen extension, can start at around £1,200 to £1,500 per square metre. However, this cost can increase depending on factors like location, finishes, and specific design requirements.

Two-Storey Extension

Adding a second storey to your extension will naturally be more expensive due to the additional materials and labour involved. Costs for a two-storey extension can range from £1,400 to £2,500 per square metre or more.

High-End Extensions

High-End or complex extensions typically cost more than the above. If you’re looking for a more luxurious or intricate design, be prepared to allocate a higher budget. High-end finishes, custom materials, and unique design elements can significantly increase the overall cost.

Additional Costs to Consider

Beyond the average cost of adding an extension to your home, there are several additional expenses that some homeowners often overlook.

Design and Architectural Fees

Hiring an architect to design your extension is essential for ensuring a well-planned and aesthetically pleasing project. Architectural fees typically range from 10% to 15% of the total project cost.

Party Wall Agreements

If your extension shares a wall with a neighbouring property, you may need to obtain a party wall agreement. This legal requirement usually requires legal advice and can therefore incur additional costs.

Contingency Fund

It’s wise to set aside around 10% of your budget as a contingency fund to cover unforeseen expenses or design changes that may arise during the construction process.

House extension costs

Financing Your House Extension

Given the potential costs involved, financing your house extension is a crucial consideration. Homeowners often explore the following options:

Using Your Savings

If you have substantial savings, using your own funds might be the most straightforward way to cover the costs.

Remortgaging Your Home

Refinancing your existing mortgage or taking out a new one can provide the necessary funds. This can be a cost-effective solution if mortgage rates are favourable.

Taking Out Personal Loans

Some homeowners opt for personal loans to cover extension costs. While this provides quick access to funds, interest rates and repayment terms should be carefully considered.

Using A Home Improvement Loan

Specific loans tailored for home improvements are also available. These loans often offer favourable terms and may be an attractive option.

Taking Advantage Of Equity Release

If you’re an older homeowner, equity release schemes can provide funds based on the value of your property. However, this option comes with long-term financial considerations and should be approached with caution.

How much does an extension cost

A house or home extension can be a transformative project that enhances your living space and property value. However, understanding the potential costs is essential for successful planning and execution. By considering factors such as the type of extension, location, materials, and additional expenses, you’ll be better equipped to budget effectively and make informed decisions.

Remember, each house extension project is unique, and costs can vary widely based on individual circumstances. Seeking advice from professionals, obtaining accurate quotes from contractors, and conducting thorough research will help you navigate the financial aspects of your extension journey. With careful planning and a realistic budget in mind, you’ll be on your way to creating the dream living space you’ve always envisioned.

As a UK homeowner, one of the most significant investments you can make is remodelling your home. If, today, you’re wondering ‘how much does an extension cost?’, the good news is we are here to help. We have a proven track record of success helping people like you create the living space they’ve dreamed of.

If you’re planning to redecorate or renovate this summer, get in touch with Red Box via phone or email to discuss your project.