How Much Does a House Extension Cost 2026 Guide

Adding an extension to your home can be a great way to add space and value. Before starting any planning or work, we recommend carefully considering the cost vs. the potential return on investment (ROI) to make sure you’re happy with how the numbers line up. After all, will you make your money back if you’re hoping to sell in the near future?

Another thing to consider is whether the extension will give you the space you need for a reasonable price, or if would it be wiser to sell up and move to a home that suits your needs better (and avoid the stress and inconvenience of building works). Answering these questions should help guide you to whether a house extension is your best option.

To help answer these questions and to know whether or not to proceed, the main questions to such a big expense are; how much does a house extension cost and is it worth it?

How Much Does an Extension Cost?

There are many factors that play into how much an extension to your home will cost, no matter if it’s a loft extension or rear extension. To get an accurate quote for the work, it’s best to have a professional, like an architect, draw up the plans so you’re being quoted for exactly what is needed.

However, this isn’t always possible. Estimating the cost of an extension without access to architectural plans will always be an approximate guide. But there are some things that can impact how much you’d pay:

The size and shape of your extension
Your choice of materials
Whether there are any unusual or premium design features
The type of roof selected
The amount of glazing required
Labour costs
Your location in the country
Site access
The standard of build selected
Finishes such as roof lights and underfloor heating.

There are other factors which can affect the cost of your extension like seasonality and current UK financial situation but these you can’t control. We have researched current figures on several standard extension builds to give an idea of how much this type of project could set you back.

How Much Does a Single-Storey Extension Cost?

A single-storey extension is ideal for adding kitchen space or creating an open-plan living area on the ground floor.

According to figures recently released by Homebuilding and Renovating, a simple box-shaped single-storey extension typically costs around £1,000 to £2,000/㎡, although this figure will vary depending on where in the UK you live. This cost will rise considerably if you opt for an exceptionally high-quality build or add unusual design elements like a giant skylight or a highly bespoke kitchen.

Some single-storey extensions will not require planning permission, depending on ‘permitted development rights’. In most cases, a rear extension that does not exceed three metres — or four metres on a detached house — will probably not need permission but we always recommend checking with your local planning authority (LPA) through your local council. As long as you do not live in a conservation area, you may be allowed an extension between six and eight metres, but you will need to contact your LPA to obtain approval. Anything larger, more complex or that is to be built in a conservation area will require planning permission, which attracts a fee of £258 in England and Wales.

How Much Does a 2-Storey Extension Cost?

The cost per metre squared should not be much more for a two-storey extension than for a single-storey extension. You will need excavation work and roofing for both projects, so aside from the extra walls and interior fixtures, there is little extra to fund. Consequently, a two-storey extension represents a higher ROI because it will add more value to your home than a single-storey build while only marginally increasing the cost; a two-storey extension will not cost double the price of a single-storey build.

In August 2020, the government relaxed planning permission requirements for two-storey extensions. You will not require planning permission if you stay within permitted development guidelines. However, all side extensions that exceed one storey require planning permission.

Other house extension costs

Other than a more general single or two-storey extension, there are other more specific extension options you could consider.

Conservatory extension cost

Building a conservatory to the rear or side of your home could be the perfect extension. Generally built as a playroom for your little ones, an alternative dining room or even a sunroom for relaxing, a conservatory can be an excellent addition and add value to your property. Depending if you would like an uPVC or wooden conservatory, and depending on the style you choose, a conservatory can cost an average of £10,000 to £16,000 to build.

Rear extension cost

A rear extension can be used for many things such as a utility room, dining room, study, playroom, kitchen, living room or a combination of any of these. Based on that it can be multipurpose, as well as the quality of finish and size of your extension, costing a rear extension can be a challenge but on average, it can cost between £30,000 and £100,000.

Kitchen extension cost

Whether you’re looking for a new kitchen space, or to extend your current one, a kitchen extension could be a perfect option for you. It’s similar to a general rear or single-storey extension but a large part of the cost will depend on which kitchen you choose to design and install. On average, a kitchen extension will cost between £25,000 and £35,000.

Porch extension cost

A porch to the front of your house can be the perfect addition to your home, adding storage space for your shoes and coats. The costs for building a porch or extending your existing porch can vary depending on the material you choose (brick vs uPVC) and how big it’ll be. But as general guidance, a porch can cost you between £2,000 and £8,000.

Garage extension cost

The cost of a garage extension can vary on whether you’re extending an existing garage or building a brand new garage. It can also vary depending on the materials you’re choosing (such as wood, metal or bricks) and whether the garage will be pre-fabricated. On average, it will cost in the region of £3,000 to £20,000 to add a garage to a home.

Additional Costs of Extending Your House

In addition to the cost of materials and labour required to build your extension, you should factor in a contingency fund for unexpected costs such as your groundworks costing more. Plus, we recommend adding some extra budget for optional services you might decide are a worthwhile investment such as buying professional architectural drawings. You are not legally required to use an architect, but having one on board can help things run smoothly and may save you costly mistakes, especially if they are able to project manage the works as well. Even a seemingly small extension can be surprisingly complex if you have little experience in managing such a project.

Additional costs you may be liable to pay include:

Here is a further breakdown of some additional costs you may be responsible for should you choose to have an extension:

Party Wall Agreement — if the extension affects a wall you share with a neighbour. These range from £700 to £1,500 per neighbour.
Planning Permission — currently £258 in England and Wales as long as the works stay within your existing boundaries.
Architectural Drawings and Designs — these vary considerably but typically run into thousands of pounds.
Building Control Certificate — required upon completion of a double-storey extension and costs £750.
Lawful Development Certificate — proof that your building work is lawful without obtaining planning permission; costs £103.
Ecology Report — if the local authority thinks your building work may affect local wildlife.
Historic Building Report — if your property is listed or located in a conservation area.
Flood Risk Assessment — if you live in a high-risk area.

There may be further costs that are unique to your build and where you live.

How Much Does an Extension Add to the Value of a House in the UK?

Did you know that most people building an extension are not doing so to sell it straight away, but instead want to enjoy the space first? This might mean that although you’re thinking about whether or not you’ll be making your money back, you’re unlikely to know for a few years until you are ready to sell. But in general, the good news is that yes, when you’re ready to sell, a house extension will just about always add value to your home (as long as you are careful about your spending) and you will get back the money you spent.

However, it’s easy to overspend on building works if you don’t seek professional advice, which could result in you not adding as much value to your home as you spent on the work. Crunch the numbers and do your research before committing to an extension to make sure that the building costs will not exceed the value added. Costs can especially escalate if you opt for a complex build of the highest quality. And don’t forget to factor in the ceiling price for your area — no matter how beautiful your extension is, you’re unlikely to exceed this when you sell.

The inconvenience and stress of extending should not be underestimated either. The work can take months to complete — typically six months or more for a two-storey extension. So, it’s important to ask yourself; can you cope with the disruption for that length of time, and is the financial payoff worth the upheaval?

Is It Best to Extend or Move House?

There is no “right” answer to whether it is best to extend your current home or move to a new one. The key to deciding is to research both options thoroughly.

Speak to the relevant professionals, such as architects and surveyors, to find out how much work is involved in achieving the outcome you want, how long it will take and how much it will cost. Be sure to factor in all potential costs, not just the basics of materials and labour. We also recommend speaking to any neighbours who have recently carried out similar work on how much it cost them and whether they’ve had their house revalued as this can provide you with real local information.

We also recommend researching the local market and finding out what the ceiling price for your area is. No matter how much you spend, you’re unlikely to be able to break this ceiling price and therefore not make back the money you’ve invested. Also, consider your lifestyle and how easy it would be to live on a building site for several months, and what the impact of the extension will be on your daily lives. Is the upheaval during the work going to pay off in the long run?

Ultimately, whether investing in an extension is worthwhile will depend on:

The ROI — will the value added significantly exceed the total cost of the building works?
The Inconvenience — can you live with the disruption for the time required to complete the project?
The Result — can you achieve the result you want by extending your existing property?

Before making any final decisions, take the time to research the alternative, i.e. selling your home and moving into a larger property. Can you afford to buy the type of home you want? Is it more economical to extend your current home or move straight into a new property that offers just what you need?

If the thought of endless red tape, disruption and stress, not to mention the pressure of balancing the books, fills you with dread, and you decide to move house is the best option, House Buyer Bureau can help you sell your house fast.

We can buy your property in as little as 7 days so you can quickly move on to find your new dream home. If you sell your home to us for a cash price, you’ll become a chain-free buyer so you’ll be in an excellent position to negotiate the price on a property that offers the space you need — without the hassle and expense of building works!

Chris

Chris has worked in property all his career, first as a successful estate agent before spotting a gap in the market for buying property directly from people looking for a simple, quick sale.

He has a passion for property and as an experienced valuer, has looked at well over 50,000 properties so far at HBB. He has extensive experience in property buying and regularly comments in the press on property matters, trends and promotes ways to simplify and speed up the selling process.

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How much does a house extension cost UK 2026