House Extension Cost

Trying to find out how much a house extension costs? Trying to get accurate extension quotes can be tricky with so many options - but MyJobQuote is here to help.

In this guide, we break down extension prices for all the different types, including rear, lean-to, side return, wraparound, porches, garages, and even conservatories.

Even if your house extension plans are far in the future, it's never a bad idea to look at some house extension cost examples to give you an idea of your total costs.

Getting free, no obligation quotes from local builders couldn't be easier with MyJobQuote. Just submit a few basic details, and find builders near you for quick and easy house extension quotes.

How Much Does an Extension Cost in the UK?

The average cost of a house extension in the UK is around £40,000, although the total cost will depend on your project.

You can expect the cost of a house extension to depend on:

• The size of the extension
• Type of extension (e.g., side-return extension vs. kitchen extension)
• Quality of finish (e.g. low- or high-end materials)

As a general guide, house extension costs per m² fall within the following ranges:

• Basic Finish - Extension costs in the UK are typically around £1,500 to £2,000 per m².
• High-End Finish - The better the finish, the higher the cost, with the average extension cost per m² falling between £2,000 to £3,000 per m².

House Extension Prices

Let's take a closer look at some house extension cost examples to give you an idea of the budget you may need to set aside for your project.

Compare Extension Costs by Type

The type of extension you choose will come with different costs to consider - for example, multi-storey extensions are going to amount to more than adding a basic porch to an existing structure - however, the extension cost per m² will be lower.

The following table shows house extension costs per m² for different types of extension, assuming a good quality finish throughout:

Compare Extension Costs by Finish Quality

The quality of the finish will have a big impact on the final price per square metre of your home.

What Is the Cost of Building an Extension? (Labour Only)

The overall costs for labour will vary a great deal depending on the exact nature of the work that you have completed.

The following is a rough idea of costs and timescale, although more complex structures are likely to take longer. It's worth noting that labour fees in London and the South East are higher than the national average.

Average Extension Labour Costs and Timeframes

Hourly Rates for Different Types of Tradespeople

Types of House Extension

Once you've decided that you want to get an extension built on your house, the next step is to decide what sort of extension you want.

Lean-To House Extension Cost (Rear or Side)

A lean-to extension typically adds a single room to the back of the building. The roof is most often pitched, which is the reason for the name. A lean-to extension is a good choice if you only require a small side extension. The cost of an extension like this is usually between £25,000 and £40,000, whereas a rear extension may become more expensive.

Pros

• ✔ Offers flexibility
• ✔ Easily add a single extra room

Cons

• ✖ Size is limited by garden space

Side Return House Extension Cost

Some homes have alleyways that run down one side of them. You often find these in Victorian terraces. Most homeowners use them to store their bins. In this extension, the alleyway is used to extend the ground floor of the home.

On average, a side extension costs between £15,000 to £25,000. Because this tends to be a smaller type of extension, the total cost will tend to be lower than other options.

Pros

• ✔ Quick and cheap option
• ✔ No garden space sacrificed

Cons

• ✖ Only adds a limited amount of extra space
• ✖ Only an option for some homes

Prefab Extension Cost

It is possible to create your extension off-site, and then just install it by using cranes to lift the pieces into place.

The average cost for a prefab extension is around £2,000 per m².

Pros

• ✔ Quick and easy installation
• ✔ Minimal disruption for you and your neighbours

Cons

• ✖ Need access space for a large crane
• ✖ Limited options

Loft Conversion Cost

A loft conversion is often the most cost-effective way to add space to your home. The amount of space you gain will depend on your existing loft and the type of conversion you choose.

The average loft conversion costs around £40,000, but a basic loft conversion can cost as little as £15,000.

Pros

• ✔ Cheapest cost per m² gained
• ✔ No loss of outdoor space

Cons

• ✖ Available space depends on the style of roof
• ✖ Can be expensive to make more awkward spaces usable

Kitchen Extension House Extension Cost

One of the most common uses for an extension is in the kitchen. This can involve extending and remodelling the existing kitchen. The cost of a kitchen remodel varies largely based on the quality of the fittings and appliances chosen for the kitchen. The costs range between £25,000 and £100,000.

Pros

• ✔ Good opportunity to create an open plan kitchen and dining room
• ✔ Can rearrange the kitchen to suit your needs

Cons

• ✖ Can be the most expensive type of extension

Wrap Around House Extension Cost

A wrap-around extension is when you extend to both the rear and the side of your home at the same time. This creates a lot of extra space in your home. It is ideal for creating large open-plan living spaces. The average extension cost is £40,000 to £100,000.

Pros

• ✔ Creates lots of space
• ✔ Flexibility of design

Cons

• ✖ Expensive

Single-Storey House Extension Cost

A single storey extension is an extension that only expands your ground floor space. Their roofs can be completely separate from the main roof of your home. The cost of a single storey extension is £15,000 to £100,000 depending on which type of extension you choose.

Pros

• ✔ More roofing options
• ✔ Quicker to build

Cons

• ✖ Higher cost per metre square

Double-Storey House Extension Cost

Lean-to and wrap around extensions can be built as two storey extensions. If you want to go even further, you can also get the loft space made into a liveable space. The average cost of a double storey extension is £40,000 to £50,000 for a lean-to extension and £60,000 to £150,000 for a wrap around.

Pros

• ✔ Lowest cost per m²
• ✔ Creates more space for the amount of garden sacrificed

Cons

• ✖ Can be very expensive

Porch House Extension Cost

As one of the more affordable ways to extend a property, the average cost to build a porch based on one that's around 3m² is approximately £4,500. Although this price can be much higher if you have it built out of solid brickwork and install double glazing.

Pros

• ✔ Low cost and quick to build
• ✔ Can improve kerb appeal

Cons

• ✖ Limited usable space

Garage House Extension Cost

The cost of a garage extension is around £9,000 for a single-width build, although a double garage (or one with a pitched roof) can cost in the region of £13,000.

Pros

• ✔ Adds secure storage and parking
• ✔ Increases property value

Cons

• ✖ May require extensive work if repurposed

Additional House Extension Costs

When you are drawing up the budget for your project, there are a lot of other potential costs you need to keep in mind. Some of the most common additional costs are listed here.

Site Survey Cost

A site survey can be a wise investment before starting a large project like a house extension.

Professional site surveys can identify existing or potential problems early, helping prevent costly issues during construction.

The average cost of a site survey is between £600 and £1,400.

Insurance Costs

Because of all the disruption that's caused by a house extension, some people decide to stay somewhere else while the work is being completed. This will simplify things for the team that's building your extension and can be a lot more comfortable for the residents.

If you're hiring tradespeople directly, then you may also need additional insurance: public liability insurance, employer's liability insurance, and construction insurance.

The typical cost of a short-term insurance bundle like this, as well as home insurance adjustments, will be between £500 and £800.

Exterior House Painting

If your home has a painted exterior already, then you should consider getting the whole house painted once the building work has been completed. Otherwise, you'll end up with a property that looks mismatched and incomplete.

The average price for painting a house exterior is £850. Although the overall cost will depend on factors such as the size of the property, whereby a large detached home will cost far more than standard terraced houses or

House Rewire Cost

When you get an extension built, the property will need to be inspected to ensure it meets or the legal requirements. As a result, it might be necessary to update the property's wiring, especially in older properties.

The average cost for rewiring a house is around £4,000, but again the exact price you're quoted will depend on the type and size of the property.

An electrician may also recommend that you replace the consumer unit (or fuse box) if the existing electrical system won't be able to handle the demand placed on it by the house extension. On average, to replace a fuse box costs about £500.

New Boiler Cost

If your heating system cannot support the additional load, installing a new boiler may be necessary.

On average, installing a new boiler costs between £1,500 and £2,500. This estimate includes the overall cost of buying the boiler and having it installed by a specialist.

Underfloor Heating

Underfloor heating offers comfort and energy efficiency.

Underfloor heating costs around £800 to install in a standard-sized room, but the price you're quoted will vary based on the type of underfloor heating system (water-based or electric) and the size of the room.

Removing Drains

When you're having an extension built, the current location of your drains may cause a problem. But if you're not sure about where they're located and their condition, it can be worthwhile to hire a specialist to complete a drain survey.

On average, a drain survey cost will be around £250. If it turns out that you need to move a drain, then you'll need to add an extra £200 to £1,300 to the total extension cost.

New Kitchen Cost

If you wish to remodel a kitchen or install a new one in your house extension, then this will have a big impact on your overall cost. The quality and type of appliances you choose can add an extra £3,000 to £10,000.

New Bathroom Cost

Adding a full bathroom cost into your budget will increase the cost of your extension. It will add between £2,000 – £6,000 to your final price.

New Toilet Cost

Adding a toilet with a single basin is a cheap way to increase the number of bathrooms in your home. The average cost for a basic bathroom is £100 to £200.

New Utility Room Cost

Utility rooms are very handy in a home with many people. If this is something you'd like to include in your extension, you'll need to add an average of between £3,500 to £7,000 to your extension costs. This includes the costs for the extra plumbing, a sink, and new appliances.

Architect Fees

An architect is usually not necessary. However, despite there being a cost for one, most homeowners who use an architect find that their final costs are lower. This is because fewer changes are made during the process. A full set of plans also reduced the opportunities for miscommunication.

Architect prices are usually between 7% to 15% of the total cost of the project. If you're just looking for a planning drawing, then you should expect to pay between £2,500 to £3,000.

Structural Engineer

To be structurally sound, it may be necessary to have a steel beam embedded into the wall. To calculate the size of the beam, you will need a structural engineer.

Structural engineer costs are typically between £400 and £4,000, with the price mainly depending on the complexity of the work that you need completing.

Garden Waste Removal Cost

When the builders are clearing space for your new extension, they may generate a significant amount of garden waste, which needs to be disposed of.

All waste disposal might be included in the quote that a builder gives you. But if it isn't, garden waste removal costs around £200.

Skip Hire Cost

Having an extension added to your home generates a lot of general waste that needs to be removed. This is because a lot of rubble is created when the walls are broken through.

Removal of this waste might be something that the builders you're working with will handle on your behalf and include in the price they quote you. But in other cases, you might be expected to arrange skip hire yourself and pay for it separately.

If it's not included in the quote, then you should expect to pay between £250 to £450 for skip hire.

What Impacts House Extension Costs?

Building a house extension is a big project. Extension quotes in the UK are high, and the stakes feel even higher when it seems like so much can go wrong with the construction.

Here's a simple breakdown of what you can and can't influence when it comes to the overall price for your house extension:

Non-Negotiable House Extension Costs

• Type of Extension - Your extension type dictates how big the job will be. Single-storey rear and lean-to house extensions are straightforward constructions. Extensions with new plumbing and electrics (such as brand new bathrooms or kitchens) will have higher costs and longer timelines.
• Size of Extension - While double-storey extensions appear more expensive than single-storey extensions, you can make use of the ground floor build (e.g., groundworks, foundation, scaffolding) to lower your overall cost per square metre.
• Location of Property - This is something you cannot change. Labour costs are higher in London and the surrounding areas by around 10% to 25%.

Variable House Extension Costs

• Quality of Finish - You have complete control over the finish you choose for your house extension. Making cost-effective choices in your finishing details can have a big impact on your overall project costs. Premium finishes (including bespoke designs, premium glazing, and advanced smart home features) can double or even triple your costs.
• Cost of Materials/Fixtures - Shopping for supplies yourself can be time-consuming, but can yield cost-saving benefits if you do so during sale periods.

What's Involved in Building a House Extension?

Even for the most experienced DIYer, a house extension is not a DIY job.

Certain aspects of the job should only be undertaken by qualified professionals, including electrical work, plumbing, and structural alterations.

To ensure a high-quality finish and safe installation, it's best to hire a trusted local builder. With MyJobQuote, you can get multiple quotes from house extension specialists quickly and easily with no obligation to hire.

To give you an idea of your builder's process, take a look at the general steps below.

Before the Job Starts

• Planning and Preparation - Your house extension will be designed (often with an architect), and planning permission will be applied for (if required). When the plans are approved, the site will be cleared, and supplies will be ordered.

During the Job

• Foundations and Structure - This phase includes the groundworks, foundations, drainage, building the basic structure (with internal and external walls), making sure everything meets building control.
• Roofing and External Shell - Your builders will install your extension's roof, as well as windows/doors, guttering/drainpipes and rendering to make the extension weatherproof.
• Internal Works (First Fix) - This stage includes plumbing, electrics, insulation and plastering.
• Finishing (Second Fix) - The second fix will be when your electrics and plumbing are finalised (e.g., sockets are installed), and the space is prepared for final inspections.

After the Job

• Snagging and Final Checks - Your builder will walk you through your new extension and let you point out any issues (e.g., small leaks, cosmetic issues with plaster, etc.). Once identified, your builder will then fix these problems for you, and your space will be ready for use.

What Can I DIY in a House Extension?

If you want to keep your budget for your house extension project low by completing some of the work yourself, there are parts of the job that can be DIYed:

• Fitting tiles
• Laying flooring
• Basic landscaping/garden clearance
• Removing old fixtures/fittings
• Installing flat-pack kitchen units
• Painting and decorating

Building Regulations and Planning Permission for a House Extension

Building regulations will apply to any substantial work you have done on your home. Planning permission is not always needed, although it may be required in more complex structures. However, permitted development allows you to do a lot of work on your home without having to apply for permission.

Building Regulations

Building regulations aim to ensure that all homes are built up to a suitable standard. This means that when you get an extension done, building regulations will be applied to the whole of your home. Not just the new extension.

You should be aware of this, as it can add a lot of costs. Small changes can be needed, like the addition of fire doors throughout your home. However, much larger renovations can be needed, such as the rewiring of the whole house.

As the homeowner, it is your responsibility to have the work approved as meeting building regulations, which will require completing some paperwork along with passing a physical inspection. The whole process usually costs between £50 and £100.

In most cases, your lead contractor will ensure it is done. You should make sure it is clear who is taking responsibility for doing this at an early stage.

Planning Permission

Many extensions do not need planning approval, although if you do need to apply, it will cost £206 for the application. You may, however, need to set up party wall agreements with any neighbours that share an adjoining wall.

The following is a list highlighting any limitations without the need of planning permission:

• Single storey extension can extend up to 4m on a detached property and 3m on any other type of property
• The maximum height is 4m
• The new building work should be completed using similar materials to the rest of the home
• A maximum of half the garden space can be used
• A side extension can be no more than half the width of the original home

Anything beyond the above limits may be subject to approval — you can use the government’s planning portal to check for yourself.

Another option is to speak to your local council. Most have a planning department. These offer consultations to advise you about the need for planning permission. There is usually a cost of around £50 - £150.

If you live in a national park or a conservation area, then you should be aware that these limits may be much smaller.

Alternatives to a House Extension

If you want to add space to your home, but don't have the budget for the cost of a £40,000 house extension, there are other options available that cost a little less, but still give the feeling of more space.

Let's go through some low-, mid-, and high-cost extension alternatives:

Low-Cost Extensions (£10,000 to £15,000)

Summerhouse Cost

A summer house is a separate building in your garden, which could act as a bedroom or sitting room all year round.

On average, summer house costs (including supply and labour) are around £12,000.

Pros

• ✔ Can add as much as 5% to the value of your home
• ✔ Less disruption to home life during construction

Cons

• ✖ Can be expensive to make a liveable space
• ✖ Considered a luxury addition

Conservatory Cost

Traditionally, conservatories are a mix of brickwork and glass. The glass panes are similar in size to large windows, and the brickwork usually rises about 1m in height.

On average, conservatory extensions cost around £15,000.

Pros

• ✔ Quick and easy to build
• ✔ Cost-effective

Cons

• ✖ Not considered a fully habitable room (compared to regular extensions), so may not add as much value
• ✖ Can be hot in summer and cold in winter

Mid-Range Extensions (£20,000 to £30,000)

Orangery Cost

Orangeries are the predecessors of conservatories. They are made with more brickwork than a conservatory typically is, and the roof of an orangery is usually flat with a glass lantern window.

The average cost of an orangery is around £22,000.

Pros

• ✔ Can offer more light than an extension
• ✔ Provides more space than a conservatory

Cons

• ✖ Flat roofs can be difficult to maintain
• ✖ Can be more expensive per square metre than other options

High-End Extensions (£30,000+)

Glass Room Cost

Glass rooms are made almost entirely from glass. They're like conservatories, but the glass continues all the way to the ground, and there is no brickwork, creating a modern finish.

Average costs for a glass room are between £15,000 and £70,000.

Pros

• ✔ Clear views over your garden and surrounding area
• ✔ Bespoke systems

Cons

• ✖ Expensive to buy and install the glass
• ✖ Can be expensive to heat

Cost of House Extension Removal

If there is already an extension on your home, but you are not happy with it then you have two options. You can either replace the existing extension or remove it.

Removing an extension can be a big job, depending on the type and how it is integrated into your home. If the roof of the extension is joined to the main house, then you will need the services of a roofer to fix the main roof when you are done.

To remove an extension will cost between £3,000 and £5,000 for a single storey extension. For a double storey extension, the costs can be as much as £10,000.

This will cover the costs of bringing down the old extension and removing the rubble. You will then need to consider what you want to do with the open wall.

Checklist: Hiring House Extension Builders in the UK

Putting your trust into a local builder to take care of your house extension is a big undertaking. Not only are house extension costs in the UK among the highest home improvement costs, but if the workmanship is poor, you can be left with recurring structural problems for years to come.

To help shape your decision-making process, here's what we suggest when vetting potential builders:

• Are they qualified? Look for NVQ or City & Guilds training in Bricklaying, Carpentry, or Construction, Diplomas in Construction/Building Services, or apprenticeships in relevant trades.
• Do they have insurance? Your builder should have public liability insurance to cover themselves and you in the event of any issues or damages during the project.
• Are they offering you a written quote? Having your quote in writing leaves less room for hidden charges or misunderstandings. Always get an itemised breakdown of costs to see exactly what's included - and what isn't.
• Have you looked at their customer reviews? MyJobQuote makes it easy to view a trader's customer reviews on their trade profile. Take note of any comments about work ethic, timekeeping, cleanliness on site, and overall quality of work.
• What about building control? Ask if they will take care of building control for you. Most contractors will, but it's best to double-check that it's not your responsibility to avoid any confusion.
• Are the payment terms clear? Find out when and how you need to pay to prevent any hold-ups in the work starting. Make sure your deposit isn't the whole amount, but closer to 10% or 20%.
• Do they offer a warranty/guarantee? Traders should offer some sort of cover on their work if they are reputable. Make sure you know these terms before you agree to work with them.

We recommend you gather at least 3 quotes from builders near you to compare their costs. MyJobQuote makes this process easy by keeping all contractor information in one place, including customer reviews and photos of previous jobs, so you can make a choice at your own pace.

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