How Much Does a House Extension Cost per Metre (m²) in the UK?

Data submitted by WhatPrice users has revealed that £1,400 to £3,000 is the average house extension cost per m2 in the UK. 

Read our guide to discover how much you’ll pay for an extension based on whether it’s a single or double storey project. Plus, depending on the level of specification you’re aiming to achieve. 

House extension costs in the UK

Extending your property is one of the best ways to increase its value. But before going ahead, you’ll need to work out how much an extension will cost to decide how you will finance your plans. 

Average extension costs per square metre

Extension type	Typical costs per square metre
Single storey extension	£1,810-£2,850
Double storey extension	£1,440-£2,300
Rear extension	£1,440-£2,300
Side return extension	£1,500-£2,400
Wraparound extension	£1,500-£3,500
Over structure extension	£1,250-£3,00

The average single story extension cost per m2 is £1,800 to £2,850.

Surprisingly, double height extensions can work out cheaper at £1,440 to £2,300 per square metre. That’s often because hiring labour for longer and also ordering more materials creates job security for trades and suppliers alike, which will be reflected in lower costs. 

In terms of specific extension types, a wraparound extension is the most expensive to build as it adds more space along two sides of your property instead of only one. 

Regional cost differences (London vs rest of UK)

Building costs are significantly higher in London compared with the rest of the UK. 

For instance, the UK average single story extension cost per m2 is £1,810 to £2,850. Our research has shown that the cost of building work in London can be between 9% and 50% higher. 

Another option to save money is to hire a team of builders from outside of London. That’s because even with the cost of travel and accommodation included, it can sometimes still be cheaper to hire tradespeople from elsewhere in the UK.  

Extension cost breakdown: What’s included

Extension element	Typical % of the budget	Low spec build (£1,400 per square metre)	High spec build (£3,000 per square metre)
Construction costs	65%	£910	£1,950
Architect & design fees	7%	£98	£210
Planning permission & building regs	2%	£28	£60
Party wall agreements	1%	£14	£30
VAT (20% if applicable)	12%	£168	£360
Interior fit-out & finishing	10%	£140	£300
Legal costs	0.5%	£7	£15
Contingency	5%	£70	£150

Based on whether your house extension will cost closer to the lower average of £1,400 per square metre or the higher average of £3,000 per square metre, these are the typical costs you can expect to pay for each aspect.

Across the board, the construction costs will always absorb the majority of your budget. So consider whether the size and scope of your plans need adjusting based on the costs of actually building your extension.

Around 35% of the costs will cover everything else from planning to the interior finishes. 

See how much your extension will cost by using our free extension cost calculator tool! Alternatively we have written an article about house extension cost per metre here.

Cost-saving tips and budget management

New to building extensions? As one of the most expensive ways to upgrade your property, the potential costs you might be looking at can be overwhelming. 

However, by keeping a close eye on where your money will be spent, you can best control the total cost to build an extension in your specific case. 

How to reduce extension costs without compromising quality

Simple designs and standard specifications are the two points to remember if you want to build a cheaper extension. 

That’s because once you start opting for unusual designs or highly customised finishes, the costs will naturally increase. However, if you get smart from the start, you can avoid any nasty surprises where your budget is concerned. 

Choosing materials wisely

From the foundations to the interior finishes, every aspect of a house extension will be subject to a specification level. 

As you might expect, low specifications involve cheaper costs, whereas high specifications are more expensive to build. This is also one of the reasons why house extension average costs per square metre fluctuate between £1,400 and £3,000.

These are some examples of aspects that your contractors might ask you to choose, and their specification levels. 

Extension aspect	Low specification (Cheapest)	Mid specification (Average price)	High specification (Most expensive)
Foundations	Standard trench fill to Building Regs minimum depth	Higher grade concrete with additional steel reinforcement	Piled foundations with engineered waterproofing
External walls	100mm cavity wall with mineral wool insulation	150mm cavity with PIR rigid board insulation	Insulated concrete formwork (ICF) or Structural Insulated Panels (SIPs) with advanced airtightness
Windows & doors	uPVC double glazing (U-value ~1.4)	Aluminium or composite double glazing (U-value ~1.2)	Slimline aluminium or timber frames with triple glazing (<0.9 U-value)
External finish	Sand and cement render	K-Rend or timber cladding accents	Premium cladding (zinc, stone or ceramic rainscreen)
Heating	Extend existing radiator system	New radiators throughout and  programmable thermostats	Underfloor heating and zoned smart controls
Walls & ceilings	Standard plaster skim	Smooth skim with mist coat	Specialist finishes (i.e. polished plaster or feature wall panels)
Flooring	Laminate, vinyl or budget ceramic tiles	Engineered wood or porcelain tiles	Solid hardwood, natural stone, or large-format porcelain
Kitchen units	Flat pack melamine carcasses	Rigid carcasses with laminated or painted fronts	Bespoke joinery, solid wood or high-gloss lacquer
Shower & bath	Acrylic tray and electric shower	Stone resin tray and thermostatic mixer	Wet room with concealed drainage and frameless glass
Garden	Turf only	Planting beds and edging	Designed landscaping with irrigation and outdoor kitchen

For some elements, opting for better quality might be important to you. But, if your budget is strict, you’ll need to choose lower specification materials wherever possible.

Low end specification: It will keep costs down, but may lack the wow factor. Also, your home may experience higher running costs if the insulation and overall energy performance aren’t up to scratch. 

Mid range specification: Often a great compromise to ensure a good standard of finish, but without blowing the budget out of the water. It’s also the standard to aim for if you’re at risk of exceeding your area’s property value ceiling height. 

High end specification: Luxury finish and long term performance. But, easy to overspend so apply caution if you’re looking to sell soon. Depending on where the value is added, it might take time to recoup your money. 

Managing builders and contractors

If you’re prone to changing your mind about what you want, your builders are likely to charge you more for their time and effort. That’s why it’s important to finalise your plans early on, including through professional drawings and land assessments.

Also, get specific with your contractors about your specification level. For instance, saying you want a ‘white kitchen’ is vague. Instead, asking for a ‘matt white handless kitchen with quartz worktops’ is clearer for everyone. The more detail you provide, the easier it is for your builders to manage your expectations while also keeping your budget in check. 

You should also consult with your contractors about what’s included, and what’s not. Alongside materials, ask whether site clearance and waste removal have been factored into the quote. 

When to use a fixed price contract

Many homeowners are rightly worried about their extension going over budget. Working on a fixed price contract can help avoid this, as it means agreeing on a price with your builder upfront rather than paying based on the time and materials needed. 

Opting for a fixed price contract is a good idea when:

• You have structural calculations and architectural drawings to provide a complete specification of what’s needed 
• The project scope is unlikely to change
• The build is straightforward (simple shapes and no groundwork issues)
• You’re hiring a very experienced contractor 

Remember, even if you opt for a fixed price contract, you should still leave a contingency fund of at least 10%. 

House extension cost calculators

Want to see what your house extension might cost? WhatPrice users have told us their average extension prices, based on the extension type and size, plus their location in the UK.

Enter your details now into our extension cost calculator. Or, see your expected returns on your investment with our extension value calculator. 

Our calculators are free to use, and could help you see if paying for an extension is a great investment! 

Planning your house extension

In all of our house extension price guides we also cover the essential things you need to check before you go ahead. With so much focus on the cost of building an extension, it’s crucial to make sure you don’t get caught out by skipping your obligations during the planning stages. 

If you’re unsure, take a read through our other guides for more in-depth answers to the following questions. 

Do you need planning permission?

It’s likely that your extension will need planning permission. But, your local council may advise that planning permission isn’t needed if the plans fall under permitted development. There are lots of aspects of any extension which can require planning permission. But as you might expect, the larger and more complex your plans are, the more likely that permission will be required before you can build. 

Needing planning permission isn’t the end of the world, although it will add time as well as costs to the total project. 

Complying with building regulations

Even if your extension plans fall under permitted development, you’ll still need to comply with building regulations. This isn’t just the case for extensions, as approval is also needed for the likes of roofing or replacing windows and doors. 

When you use competent tradespeople, they should arrange for building control to approve the work. If they don’t, they could be liable for legal action. 

Furthermore, as the homeowner, your local authority can also make you pay for faulty work to be fixed. Ultimately, if your extension doesn’t get the right approvals, you may struggle to sell your home. 

Timeline for design, approval and construction

Our research here at WhatPrice has found that extensions take between 2 to 6 months to build. For single storey extensions, 2 to 4 months is the standard timeframe. But, it can take an additional 2 months to construct an extension which has a second floor, especially if you’ll be adding a pitched roof. 

Common delays and how to avoid them

Delays in building an extension aren’t just frustrating, as they can also be costly.

Some top tips to reduce delays when extending your home include:

• Check if your plans fall under permitted development first
• Submit complete applications (i.e. avoid missing drawings or documents)
• Allow 8 weeks for council delays
• Book planning control early
• Order materials as early as possible
• Store materials on site 
• Book trades early
• Don’t make design changes mid-project
• Try to avoid building during wet/cold months
• Get to a watertight stage as quick as you can
• Do any utility works in tandem
• Appoint a project manager and ensure clear communication

You can’t prevent every delay, but you’re more likely to experience them if you don’t get the above aspects in order before you build. 

Financing a home extension

In this guide, we’re focusing on the cost of extensions per metre (m²). But in previous guides, we’ve also explained how single storey extensions start from around £25,640. For double storey extensions, expect to pay up to £86,300 if your extension is on the larger size (i.e. 60m²).

Whatever size your extension will be, the one thing that’s for certain is that it won’t pay for itself! 

So these are some of the main ways to consider paying for an extension depending on your financial circumstances. 

Savings vs loans vs remortgaging

If you have enough savings to pay for an extension upfront, then you won’t incur any risks of taking on debt. You can also avoid paying interest on a loan. 

That all sounds great, though you’ll inevitably reduce your financial safety net, especially if a large portion of your savings will be needed. In some cases, people are tempted to cut corners when using their savings to fund an extension, since not having any backup money can feel stressful if the budget overruns. 

Where you don’t have enough savings to pay for an extension outright, then loans or remortgaging could give you the cash you need. 

A personal loan isn’t secured against your property, though can be subject to higher interest rates depending on your credit score. Most lenders offer between £25,000 and £50,000 for a personal loan, which can cover most modest extension types. Personal loans can also be used to top up your savings if you don’t have enough to fund the entire project. 

Remortgaging can provide you with a significant lump sum to cover the cost of an extension, plus any other home improvement works you plan to do. It’s not without its risks though, as if you can’t cover the repayments you will lose your home. 

As mortgage rates are cheaper than loan interest rates, remortgaging can be more advantageous. It’s something to consider when your extension is on the larger size, i.e. a double storey or wraparound extension.  

Can you add the cost to your mortgage?

Yes, it is possible to borrow more against your home to cover the cost of an extension. If your mortgage lender agrees, then this would allow you to spread the repayments over the long term. However, you would need to check whether this option truly offers a good deal. 

Your mortgage lender will want to know the exact build costs, including your required contingency fund. They will also want a current valuation of your home. Even if they agree, you’ll likely face exit fees for your current mortgage. So with everything considered, it needs to make financial sense for you. 

Help-to-build schemes and government options

At present, there isn’t any help to build schemes available from the government which can cover the cost of extending your home, as the previous scheme closed in March 2025. However, if that changes the team here at WhatPrice will be the first to let you know. 

That said, if your extension involves upgrading the energy efficiency of your home, you may qualify for several of the grants available. For instance, the government is currently offering £7,500 towards the cost of a heat pump as part of the Boiler Upgrade Scheme. 

Return on investment: Will a house extension add value?

When pricing up your expected house extension cost per m2, understanding the potential value to be gained is important. After all, if you aren’t set to make a healthy profit, extending might not be the right option for you.

Use our free extension value calculator to see the potential profit you can expect if you go ahead with an extension.  

What kind of extensions add the most value?

If you plan on living in your extended home for the foreseeable, potential value gains might not be a huge concern to you. 

However, for those looking to extract the maximum returns from extending your property, it pays to know what will boost your house price the most in the eyes of estate agents.

Top Tip:💡Many estate agents offer a valuation service for pre and post renovations. They can advise on the type of work that will increase the value of your home based on their thoughts including demand in the local area. 

Extension type	Typical value uplift	Tips to maximise value
Conservatory extension	5%-7%	Opt for a solid roof to improve insulation and ensure year-round usability. Double or triple glazing can also prevent heat loss. Try to avoid narrow doorways leading back into the home to create a better flow.
Side return extension	5%-12%	Avoid creating any narrow corridors. Keep things light and airy by adding windows or skylights.
Kitchen extension	5%-15%	If your existing kitchen is dated or has a poor layout, take the opportunity to completely re-do it. Space for dining and high end appliances can make a kitchen extension feel luxurious.
Rear extension (single storey)	10%-15%	Prioritise kitchen, dining or living room space. Open plan layouts work well and offer versatility. Aim for a seamless transition into your outdoor space. Try to match the roof and external finishes so that the extended section blends well with the rest of the home.
Wraparound extension	10%-15%	Create multiple access points to the garden. Large glazing can add both natural light and panoramic views. Keep things bright overhead with skylights, especially if any areas are north facing. Avoid building long or awkwardly shaped hallways. Ensure the wraparound section looks and feels like it belongs to the rest of the home.
Double storey extension	20%	Extend your kitchen downstairs and add or extend bedrooms upstairs. Adding a master suite (bedroom with ensuite and dressing room) can create significant value returns.

In general, increasing usable space and improving the layout flow are important. As is investing in the most in demand rooms such as kitchens and bedrooms. This is especially the case if the extension allows you to create a larger kitchen and dining area, but also add extra bedrooms upstairs.

Two storey extensions provide the most potential for value uplift, as they can add up to 20% to the value of your home.  

Conservatory extensions add the least amount of value, although are also the cheapest type of extension to do. Extending the kitchen is a great middle option, and can add up to 15% to your property value.

Don’t have the budget, space or planning permission to extend? Another way you can create more usable space in your home is through a garage or loft conversion. Adding an extra bedroom or a home office would be a great call here! 

Extension vs moving house

It’s a safe bet that if you’re considering extending or moving, something isn’t quite ticking your boxes with your current home. 

In the short term, moving is usually cheaper than extending. Stamp duty can be the deciding factor here, as it ranges between 2% to 12% depending on how much your property sells for. If you own more than one property, an additional 5% will be added, meaning you could need to pay as much as 17% for stamp duty alone. 

Extending will be the best option if: 

• You love the area and your neighbours
• You have planning permission to get the extra space you need
• You want to get involved with the renovation plans 
• You’re okay living with the disruption while the work takes place 

Moving will be the best option if: 

• You are unhappy in your current area (including due to school catchment areas/commute times)
• You’re near your postcode ‘ceiling price’ which would undervalue any work you want to do
• You want a move-in ready space
• You don’t want to live with the disruption 

Your final choice needs a lot of thought and should be a family discussion. While the cost of extending or moving will be top of the agenda, you also need to consider all of the things that matter to your lifestyle, including for the years ahead. 

FAQs about extensions costs

Still have questions about the UK average house extension cost per m2? We’ve answered the top user queries below.

For anything else, check out our other content covering the costs of hiring each trade depending on the scope of your project.