Modern rear house extension creating a bright open plan kitchen, dining and family room with rooflight, large sliding doors and a spacious layout designed for modern family living.

What Is The Average Cost Of A House Extension In The UK?

Home Extensions
July 28, 2026•8 min read

Average House Extension Costs UK: How Much Should You Expect To Pay?

Most homeowners start looking into house extensions for the same reason. The family has outgrown the space, someone needs a home office, the kitchen feels too small, or moving house simply isn't an attractive option.

One of the first questions people ask is,"How much does a house extension actually cost?"

The honest answer is that there's no single price because every extension is different. The size, design, specification and ground conditions all play a part.

However, understanding the average costs can help you decide whether an extension is the right investment or whether another option, such as a garage conversion, might offer better value.

If you're planning a home improvement project in Greater Manchester or the North West, here's everything you need to know.

What Is The Average Cost Of A House Extension?

Across the UK, a typical house extension can cost anywhere between £30,000 and £100,000+, depending on the size and complexity of the project.

As a rough guide:

  • Small single storey extension: £30,000 to £50,000

  • Larger single storey extension: £50,000 to £75,000

  • Double storey extension: £60,000 to £100,000+

These figures usually cover the main construction work but can increase depending on the finish you choose and any additional structural work required.

For example, adding large roof lanterns, bi-fold doors, premium kitchens or extensive steelwork will all increase the overall cost.

What Affects The Cost Of An Extension?

No two homes are the same, so extension prices vary considerably.

Some of the biggest factors include:

The Size Of The Extension

A larger extension naturally requires more materials, labour and time, making it more expensive than a smaller project.

Ground Conditions

If foundations need to be deeper because of poor ground conditions or nearby trees, costs can increase before construction even begins.

Structural Work

Many extensions require steel beams to support the existing property when walls are removed. Larger openings generally mean more structural work.

Kitchens And Bathrooms

If your extension includes a new kitchen, utility room or bathroom, plumbing, drainage and electrical work will add to the final cost.

Internal Specification

Flooring, lighting, decorating, doors and kitchen finishes all influence the overall budget.

Rear house extension in Radcliffe creating a spacious open plan kitchen and living room with rooflights, vaulted ceiling and large sliding doors.
This rear extension in Radcliffe transformed a traditional layout into a spacious open plan kitchen and living room, giving the homeowners more room to relax, entertain and spend time together while filling the space with natural light.

What Do You Get For Your Money?

Unlike many home improvements, an extension doesn't just improve one room. It completely changes how your home functions.

Homeowners commonly use extensions to create:

  • Open plan kitchen diners

  • Larger family living spaces

  • Utility rooms

  • Home offices

  • Extra bedrooms

  • Downstairs shower rooms

  • Children's playrooms

Imagine a family whose kitchen feels cramped every evening. Homework is spread across the dining table, someone is cooking, another person is trying to work from home, and there's simply not enough room.

A rear extension could create one large open plan living area where everyone has their own space without feeling on top of each other.

For many families, that's life changing.

Is An Extension Better Than Moving House?

Moving home often sounds like the easiest solution until you calculate the true cost.

Besides buying a more expensive property, you'll also face estate agent fees, solicitor's costs, stamp duty, removals and months of disruption.

If you already love your location, your neighbours and your children's schools, extending your existing home can often make much more financial sense.

Rather than starting again somewhere new, you're investing in a property you already enjoy living in.

Modern rear kitchen extension in Prestwich creating a spacious open plan kitchen with a large island, improving family living, entertaining space and everyday functionality.
This rear kitchen extension in Prestwich transformed the home with a spacious open plan kitchen and island, creating a bright, sociable space that's perfect for cooking, entertaining and everyday family life.

Garage Conversion Or House Extension?

This is one of the biggest decisions homeowners face.

If you already have an attached or integral garage that isn't being used to park a car, converting it could provide the extra room you need without the higher cost of building an extension.

Across Greater Manchester and the North West, a standard single garage conversion typically costs between £12,000 and £15,000 plus VAT, making it significantly more affordable than most extensions.

For example, if your family simply needs a home office, bedroom, snug or playroom, converting the garage could provide exactly the same practical benefit while saving tens of thousands of pounds.

However, if your goal is to create a much larger kitchen diner or dramatically increase the size of your home, an extension may still be the better option.

The right choice depends entirely on how you want to use the space.

Modern rear kitchen extension in Eccles creating a larger, brighter kitchen with a rooflight, improved layout and more practical space for everyday family living.
This rear kitchen extension in Eccles transformed an outdated kitchen into a bright, spacious family hub, creating more room for cooking, dining and everyday life.

Does A House Extension Add Value?

A well designed extension can increase your property's value, particularly if it improves the way the home functions.

Buyers are often willing to pay more for homes with:

  • Larger kitchens

  • Open plan living spaces

  • Additional bedrooms

  • Extra bathrooms

  • Better family layouts

However, it's important not to focus purely on resale value.

Most homeowners extend because they want to improve their everyday lives.

Being able to enjoy your home for many years before selling can be just as valuable as any financial return.

Planning Permission And Building Regulations

Many homeowners assume they'll automatically need planning permission for an extension.

In reality, some extensions fall under Permitted Development, while others require a planning application.

This depends on factors such as:

  • The size of the extension

  • Its position on the property

  • Previous alterations

  • Whether your home is listed or in a conservation area

Building Regulations approval is normally required regardless of whether planning permission is needed.

These regulations ensure the extension is structurally safe, energy efficient and suitable for everyday living.

A professional builder will guide you through this process before work begins.

Real Project Example From Greater Manchester

We've completed numerous extensions throughout Greater Manchester and the North West, helping homeowners create larger, more practical living spaces without the need to move.

One recent project involved extending a family home to create a spacious open plan kitchen, dining and living area. The homeowners loved their location but had completely outgrown their existing layout.

The finished extension transformed how they used their home, creating one bright, social space where the family could cook, eat, work and spend time together every day.

It's a great example of how an extension isn't simply about adding square footage. It's about improving the way you live.

Rear, side and upper house extension in Rochdale creating a larger family home with an open plan kitchen and dining area, increased living space and improved natural light.
This rear, side and upper extension in Rochdale transformed the property into a spacious family home, adding valuable living space, a bright open plan kitchen and dining area, and a modern exterior to match.

Frequently Asked Questions

How much does a house extension cost in the UK?

Most extensions cost between £30,000 and £100,000+, depending on size and specification.

Is it cheaper to extend or move house?

For many homeowners, extending is more affordable than paying moving costs, stamp duty and purchasing a larger property.

Is a garage conversion cheaper than an extension?

Yes. A standard garage conversion typically starts from £12,000 to £15,000 plus VAT, making it considerably less expensive than most extensions.

How long does an extension take?

This depends on the size and complexity of the project, but most extensions take several months to complete.

Modern kitchen extension in Prestwich creating a spacious open plan kitchen, dining and living area with rooflights, increased natural light and a layout designed for modern family living.
This kitchen extension in Prestwich transformed the home into a bright open plan kitchen, dining and living space, creating the perfect setting for family life, entertaining and everyday living.

Will I need planning permission?

Some extensions are covered by Permitted Development, while others require planning permission.

Do Building Regulations apply?

Yes. Building Regulations approval is normally required for house extensions.

Can I extend if I have a detached house?

Yes. Detached homes often provide more flexibility when planning extensions.

Does an extension increase property value?

A quality extension can increase your home's value while making it more attractive to future buyers.

What rooms are most popular in extensions?

Open plan kitchen diners, family rooms, utility rooms and home offices are among the most popular choices.

How do I know whether I need an extension or a garage conversion?

It depends on your goals. If you need a larger footprint, an extension may be the better option. If you already have an unused garage, a conversion can often provide the additional room you need at a much lower cost.

Why Choose Convert Your Garage?

Established in 2002, Convert Your Garage has helped homeowners across Greater Manchester and the North West create more practical living spaces through garage conversions and home extensions.

We've completed 4,315+ garage conversions, won33 industry awards, and every project is backed by a 10 year warranty. From the initial survey through to completion, our experienced team manages every stage of the project to make the process as smooth as possible.

Final Thoughts

The average cost of a house extension in the UK varies depending on the size, design and specification, but it's important to think beyond the price alone.

The best home improvement is the one that solves your family's needs both now and in the future.

For some homeowners, an extension is the perfect solution. For others, an unused garage could provide the extra room they need for a fraction of the cost.

The best place to start is with professional advice based on your property, your budget and your long term plans.

Side extension in Bury creating a self contained annexe with a bedroom, kitchenette and bathroom, allowing the homeowner's mum to live independently while staying close to family.
This side extension in Bury was built to create a self contained annexe for our customer's mum, complete with a bedroom, kitchenette, bathroom and its own private entrances, allowing her to live independently while remaining close to her family.

How To Contact Convert Your Garage

Whether you're considering a house extension or wondering if a garage conversion could achieve the same result, we're here to help.

Call us:
0161 766 6518

Visit our website:
https://www.convertyourgarage.com

Follow us for inspiration and recent projects:

Facebook:
https://www.facebook.com/convertyourgarage

Instagram:
https://www.instagram.com/convertyourproperty/

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https://www.tiktok.com/@convertyourgarage

Established in 2002, we've completed 4,315+ garage conversions, won 33 industry awards, and provide every customer with a 10 year warranty for complete peace of mind.

Get in touch today to arrange your free, no obligation survey and discover the best way to add space and value to your home.

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Giorgia

Giorgia is the Social Media Manager and Blog Writer at Convert Your Garage. She creates informative content based on real projects and industry knowledge, helping homeowners make informed decisions about garage conversions and home improvements.

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