In this detailed house extension cost guide we examine all the factors that impact the price of a home extension. In the UK most people pay between £1,500 and £3,000 per square metre but this can vary a lot depending on size, location and the materials used.
Planning permission, professional fees and the type of extension you decide on all directly affect the total home extension cost. With so many people looking to increase the space in their property understanding these factors is vital. A well finished house extension will not only provide extra internal space it can also dramatically increase the property’s value.
With over 20 years of experience Disha Construction Ltd is happy to pass on our knowledge and understanding of house extensions so that you can make an informed decision for your own home.
Average House Extension Cost Overview
Costs for house extensions vary based on size, design and geographical location. If you know what determines house extension prices you will have a much easier time avoiding nasty surprises.
House Extension Cost Per Square Metre
Most builders quote by the square metre. In the UK a basic extension typically costs between £1,800 and £3,000 per square metre. This is usually just for the shell of the structure.
If you want a premium finish or a more intricate design expect to pay £3,000 per square metre or more. Price increases happen due to things like poor access, tricky existing structures or bespoke features. Kitchens and bathrooms will always cost extra.
Here’s a quick guide:
| Finish Type | Approx. Cost per m² |
|---|---|
| Basic | £1,600 – £2,500 |
| Mid-range | £2,500 – £3,000 |
| High-end | £3,000+ |
Usually, these numbers include VAT and basic fees. Planning, surveys and anything unusual will cost extra.
Single vs Double Storey Extension Costs
Single storey extensions come in cheaper since there is less structure being built. For a single storey extension budget £35,000 – £65,000 for a 20m² to 25m² addition.
Double storey extensions cost more overall but the second floor is often a bit cheaper per square metre because you’re already paying for the foundations and roof. A 20m² double storey usually lands between £60,000 – £110,000.
Here’s a simple breakdown:
- Single storey: £1,700–£2,500 per m²
- Double storey: £2,200–£3,200 per m²
If you’re adding rooms that need plumbing such as kitchens and bathrooms costs will rise for both.
Regional House Extension Cost Variations
The location of the property has a huge influence on the house extension cost. London and the South East usually top the charts for labour and materials and can be up to 30% more than the North. Those in cities tend to pay higher fees for permits, services and for delivering materials.
Local labour rates, delivery costs and the challenges of building in urban locations all play a part. It is worth getting a few quotes from local builders to get an understanding of what the project will entail.
Key Factors Influencing House Extension Cost
Several big variables will shape your extension’s final price tag. Design complexity, your choice of materials and finishes and what you pay for skilled trades all matter.
Design Complexity
If you keep things simple your wallet will thank you. Basic, single-storey extensions usually come in cheaper because the structure and paperwork are simpler. Once you start adding extra floors or custom features both labour and material costs shoot up.
Want unusual shapes, big windows, or skylights? Those increase the price. Changing the existing layout by knocking down supporting walls can mean more engineering and special permissions. The more detailed your drawings the higher the architect’s bill.
Here’s a quick table:
| Design Type | Cost Impact |
|---|---|
| Single-storey, basic shape | Lower |
| Double-storey, complex shape | Higher |
| Unusual features (glass, etc) | Higher |
If you plan carefully and work with a good architect you can sometimes keep these costs in check.
Materials and Finishes
Materials and finishes make a huge difference to your final bill. Standard bricks, uPVC windows and asphalt tiles will keep costs down. If you want natural stone, hardwood or fancy glass your budget needs to stretch.
Flooring, doors, worktops and even paint can swing wildly in price. Even a small upgrade like switching from paint to tiles can add up.
Some materials are harder to install than others. If they’re heavy or fragile, labour charges may go up because installers need extra care or skills.
Labour Charges
Labour often eats up a big chunk of your budget. The number of tradespeople, their expertise and local wage rates all count.
Specialists like electricians or plumbers usually charge more than general builders. If your build involves steelwork, high ceilings, or awkward access, expect more hours on site and a bigger bill.
Some builders tack on project management fees which can add cost but might save you hassle. In busy cities and the South East labour rates are usually higher than in the countryside.
Types of House Extensions and Their Costs
House extensions come in many different styles with each having its pros and price points. Size, materials and design choices all play a role in the final figure.
Rear Extensions
Rear extensions are a great way to link your home to the outside space. They are great for larger kitchens, dining rooms or just more living space.
In the UK, single-storey rear extensions usually cost £30,000 to £55,000. Double-storey versions can run from £48,000 up to £100,000 depending on size and finish.
Many rear extensions don’t need planning permission if you follow certain rules which saves time and money. The price will increase if you need structural changes or live in London or the South East.
Side Return Extensions
Side return extensions fill that skinny alley down the side of many terraced or semi-detached houses. This can make your kitchen or living area wider without sacrificing the garden.
Most single-storey side returns start at £35,000 to £65,000. If you want bespoke layouts, big glass doors or skylights the cost naturally rises.
Sometimes drains or meters will need moving which adds expense. These are super popular in cities where land is tight and people want more light. It’s a clever way to use dead space.
Wraparound Extensions
Wraparound extensions link a rear and side return of a building meaning you get an L-shaped space. They’re perfect if you want a big family kitchen or an open-plan living area.
Costs are higher because these projects are bigger and trickier. Expect to pay between £55,000 to £120,000. Roof shape, finishes and structural work all affect the price.
You will probably need a structural engineer and a party wall agreement if you share a wall. These can add loads of value and space but be ready for a longer build.
Basement Extensions
Basement extensions mean digging down to add a whole new level under your house. You get loads of space without losing the garden. This luxury comes at a premium and is the most expensive type of home extension.
Expect to pay £250,000 to £500,000 or more depending on how deep you go, waterproofing, and soil conditions. Underpinning, ventilation and light wells all add to the bill.
These projects always need planning permission and have strict safety rules. People in cities often pick this route when building up or out isn’t possible. It’s disruptive and can take months so patience is key.
Planning and Legal Considerations
Extending your house means jumping through a few legal hoops which can affect both your costs and timeline. You will need to budget for permissions, regulations and maybe agreements with the neighbours.
Planning Permission Fees
Most extensions need planning permission unless they fit “permitted development” rules. In England applying for planning permission usually costs about £200 for most homeowners. This is non-refundable even if permission is denied.
Don’t forget extra costs like architect or surveyor fees to draw up plans. These can run from £500 to £2,000 depending on how tricky your extension is. Councils often take up to eight weeks to decide.
If you have to change your plans partway through expect to pay again. Delays here can throw off your whole project schedule and budget.
Building Regulations Costs
Building regulations are a separate hurdle from planning permission and are equally unavoidable. The council checks your extension for safety, energy efficiency and structural soundness.
The application fee for building regs usually falls between £300 and £750. That covers at least one site visit from an inspector or the council.
Some councils charge more for extra visits or complicated work. Skip this step or miss the standards and you could be fined. We advise getting written quotes from private inspectors if you are not using the council.
Party Wall Agreements
If your extension touches a shared wall or boundary you will need a Party Wall Agreement. The Party Wall etc. Act 1996 says you must give your neighbour written notice at least two months before work commences.
If your neighbour’s happy with the proposal there is usually no fee. If they object or want a formal agreement both sides usually hire a surveyor. Expect fees of £500 to £1,500 per surveyor.
If both sides have surveyors you will likely be liable for both bills. Not following this process can mean delays or legal headaches. Talking early and clearly with neighbours can prevent drama later.
Additional Home Extension Costs to Anticipate
Extra costs are not uncommon and can quickly affect the project’s budget.
Architect and Structural Engineer Fees
A professional design is almost always needed for a home extension. An architect draws up detailed plans and ensures the design meets all building regulations.
The architect’s fees usually fall between 5% and 15% of your total construction costs. This range depends a lot on how complex the job is and where you live.
A structural engineer checks that your extension will stay safe and stable. They create calculations and technical drawings which the council or building inspector often requires.
Fees for a structural engineer typically start at about £400. The cost can climb depending on the size and complexity of your project.
| Professional | Estimated Cost |
|---|---|
| Architect | 5%–15% of project cost |
| Structural Engineer | £400+ |
Site Preparation and Clearance
Before building begins you need to prepare the site. This might mean removing old structures, clearing garden debris or levelling out uneven ground. Small jobs might only set you back a few hundred pounds but large or tricky sites (especially those with poor access) can easily top £1,000.
Hazards like asbestos or contaminated soil increase the risk to workers and therefore the price. Sometimes specialist removal teams will also be required to remove hazardous waste.
Waste removal adds another cost. Most services charge by skip or truckload and local council regulations can affect how you dispose of waste which sometimes leads to extra charges.
Utility Relocation
If your extension interferes with water pipes, gas lines or electricity cables they will likely need to be moved. Shifting a simple water pipe can cost a few hundred pounds.
More complicated jobs, especially with gas or mains electricity can be £1,000 or more. Sometimes utility companies insist on doing the work themselves which means possible waiting periods and extra costs.
IIt is recommended that you check where all your main services run before you start. Missing this step can cause some timely delays so budget for a bit of extra time and money just in case.
Frequently Asked House Extension Cost Questions
House extension costs change wildly depending on size, location and materials. There are many questions commonly asked when it comes to home extension costs and we have helpfully collected the main ones.
How much does a single storey extension typically cost in the UK?
On average, a single storey extension in the UK costs between £1,800 and £3,000 per square metre. For a basic 20m² extension expect to pay between £35,000 to £50,000 all-in. This price covers both labour and materials.
What are the average costs per square metre for a house extension in the UK?
Most UK house extensions run from £1,800 to £3,000 per square metre. The finish level, the complexity of the build and your location can all move the price up or down.
How can I calculate the estimated cost for a rear house extension?
It’s pretty straightforward: multiply your total floor area by the average cost per square metre. For example a 30m² extension at £2,000 per square metre comes to about £60,000.
What budget should I consider for a 24m² house extension?
With a 24m² extension at £2,000 per square metre the price will be £48,000. If you go for a high end finish with expensive materials the total could easily jump to £60,000 or more.
Can a house extension be completed with a budget of £30,000?
£30,000 might just cover a small, basic single storey extension. That budget typically stretches to about 15m² to 17m² depending on where you live and what you desire.
Contact us Today!
If you are based in London and the surrounding areas and wish to gain extra space in your property, Disha Construction Ltd is here to help. With over 20 years of industry experience we can handle all house extension projects.
Please do not hesitate to contact us today to arrange a free site visit. We will then provide you with a detailed cost breakdown for the project. All of our work comes with full workmanship guarantees and we have total liability insurance.