Building plans - House extension cost

House Extension Cost Guide

Why relocate when you can just change your property? If staying exactly where you are sounds good, you need three things to ensure you get the best quote and construction possible: research, planning and reliable help. No house extension cost is minor, but with good preparation you can keep your budget at the lower end throughout the complicated process.

You can also be in control of the construction itself. While relying on the experience of your tradesperson is a good idea, you should channel everything you learn about the industry into keeping the work on track with your plans – and budget!

This is the beauty of extending your home. You have the ultimate say in exactly how the installation turns out. It’s possible to extend any part of the house in any direction. You can make an existing room larger or create new space.

Whether it’s adding an extra bedroom or expanding the living or dining room, the value of your home increases in your eyes as well as the property market. A tasteful upgrade that’s safely within building regulations not only boosts the chance of a sale in the future, but also increases the profit you could make from the property.

Let’s start with some handy information about the business of home extensions, including key costs you should make a note of.


Why build a house extension?

Modern style - House extension cost
Modern style – House extension cost

It can be a much cheaper alternative to buying a house, especially if you’re moving with your family. July 2019 saw the average price for a UK home climb to £232,970, while a double-storey extension should be around £76,000. The difference is major.

As daunting as the project may seem, considering its many stages and elements, you can make it easier for you and the professionals you hire. Here’s more detail as to what perks you can expect from extending your home.

Benefits of a house extension

Extensions can be built on top of existing rooms in the home or as an add-on to the ground floor of your property. As long as your design complies with regulations, you can then enjoy a bigger house with extra, high-value features.

Specific advantages include:

Increasing the value of your home

Effectively, adding a house extension increases your property’s size, so in turn the value will also rise. The reason for creating the additional space and how effective it is determines what the boost is to the property’s worth. However, you need to make sure that ultimate value will be greater than the cost of the extension.

Creating additional space

An extension gives you the opportunity to benefit from a larger home. Whether you want to extend your kitchen or have a bedroom or bathroom fitted, you can use the extra space throughout the year. And, once again, that addition to the property will make it more valuable and appealing to future buyers.

Avoiding the expense of moving

There’s no doubt about it, moving home is an expensive process. There are thousands of pounds in fees to be paid, including stamp duty, estate agent payments and solicitor bills. Avoid all of this by instead improving your own home and adding valuable space with an extension. You can even tailor construction to fit your vision of your upgraded property.

Bespoke home design

Look around long enough and you’ll find all sorts of styles, materials and unique ideas to improve your home with. Assess what your property will be able to accommodate. Then search for specific features – bi-fold doors, underfloor heating, insulation materials and so on – to get a range of options and prices. You can transform the space into exactly what you need without going over your budget.

DIY potential

When moving to a new house, you typically need to depend on others to get things done, like real estate agents and moving services. On the other hand, building an extension involves much you could do yourself. This means a reduced house extension cost. But you should still hire qualified professionals for the more technical jobs, like preparing your planning permission application or laying heating and electrical systems.

Types of extensions

Single storey

This is one of the simpler projects to take on and usually the least expensive. For example, if you just want to expand a downstairs area by around 4m x 5m, you’ll probably spend around £40,000 – £60,000. Beyond the cost of individual parts of the extension, you should also check building regulations.

They’re less demanding than the requirements of other constructions, assuming the project doesn’t fall entirely within your permitted development rights. If it doesn’t and you haven’t taken the right precautions, regulations can get in the way. You can find all these factors – extension processes and conditions – outlined below.


The next rank in home extensions, generally requiring double the budget and effort. It basically involves expanding your property beyond the ground floor. You can turn an upstairs bedroom into an ensuite or even add a balcony over the extended kitchen. There’s more freedom to be creative with your design, but always be wary of costs.

You’ll likely be playing with the height and width of the house, so make sure you know what the limits are. This is important with a two-storey extension. The many elements that come into play for this kind of project, affecting the structure and size of your property, means you’ll almost definitely need planning permission.

Side extension

When it comes to where to make that extension, the side of the house is a common choice. It works well for kitchen or living room expansions, adding more space to move and enjoy your home. There are several features to consider when deciding how to make the addition really worthwhile. Rooflights, sliding doors and furniture combinations can all boost the room’s appeal.

The price varies from project to project. It mainly depends on materials, construction demands and the size of the extension. UK homeowners have paid as little as £60,000 for their new spaces, but don’t be surprised if your budget estimate reaches over £400,000 for a large and complicated design.

Rear extension

Another part of the building you can extend is the back. The perks and regulations are similar to those for side extensions. More space and opportunity to adapt your home to your and your family’s needs. Since it pushes into the garden, you could invest in a bigger kitchen that leads into a garden room with access to the outdoor space itself.

You don’t need to spend more than around £50,000 for this project. This house extension cost, like any other, depends on how much change your property allows and what you want to do with that extra space. Your planning choices can ensure you stay within your budget and permitted development rights.

Wrapped extension

This combines a side with a rear extension. As the name suggests, the addition to the house wraps around it, which also means you need plenty of exterior space to make it happen – and without violating any building regulations! One rule, for example, is that the extension and all outbuildings mustn’t cover more than half of the property’s total area.

Also keep in mind that the cost will be considerably steeper than a rear or side extension alone. If, however, you do have the funds and property size to accommodate such a project, you’re only a week or two away from getting your dream home without having to leave your beloved neighbourhood. While there are other regulations to keep in mind, any upgrades you make – sideways or upwards – can make a huge difference to the property’s value and your quality of life.

Types of building materials

Brick and block - House extension cost
Brick and block – House extension cost


Also known as brick and block construction, it’s a pretty common way to build and extend a house in the UK. This means it should be easy to find tradespeople and materials for the job – at a reasonable price too.


  • Very durable
  • Heat resistant
  • Blocks noise
  • Natural thermal regulator – if the construction is thick enough, you’ll need less insulation than with a timber frame project
  • All work can be carried out onsite, so it’s also an eco-friendly option
  • Increasingly cost-effective


  • A thin brick and block structure needs insulation
  • But there are limits to how much insulation you can add – cavities between walls shouldn’t be more than 10cm
  • Prone to cracks as the masonry settles
  • Takes time to prepare the necessary materials and construct the extension with them
  • Weather easily affects construction
  • Can let in dampness

Timber frame

This option is becoming more and more popular in the UK for a number of reasons. If your main concern is managing the home extension cost, this is a good choice to go for. With careful planning and construction, it can rival masonry in convenience and efficiency.


  • Fast construction due to readymade materials
  • Easier to set an accurate budget – materials are delivered and not subject so much to weather conditions
  • Can be more eco-friendly than masonry, if you go for FSC timber
  • Precise and versatile construction
  • Better insulation – there’s a greater need to meet this requirement and, so, a good construction often means first-rate thermal regulation
  • Running costs can also be low because of good insulation


  • Expensive materials – typically priced at around £150 / m2
  • Timber frames are not as simple or easy to acquire as bricks
  • Delivery costs can pile up
  • Less eco-friendly, considering the number of trips required
  • Preparing the frames takes time – often a month or more before they’re needed
  • Wood needs more treatment and maintenance than masonry

Rooms to extend


How often are people actually happy with the bathroom that came with their house? Given the chance to improve your living space, this a change you’ll probably appreciate the most. If you have a glum little bathroom, you can transform it into a warm and relaxing place.

Expand it and add flair with new tiles, features and décor. Splurge a bit more on a bigger tub or better shower. If you have the traditional hot and cold taps, why not upgrade to a single lever system? There’s plenty you can do to make your bathroom the most welcoming space in your house.


You can expect the same huge range of options as a bathroom transformation. Browse for home improvement ideas and you’ll find that kitchens are a popular addition to the average cost of house extension projects. The boost to the overall experience and value of the property are key reasons.

It’s both a practical and social space, so the possibilities are endless. And having more room to fill means you can really make the most of a kitchen and dining room concept. Branch your market research out into several departments – appliances, furniture, décor and more. Explore different sizes, styles and smart solutions. You can turn even a minor extension into a very pleasant and practical environment.

Living room

This is another part of the house that would benefit from extra space. Sick of a cramped sofa and TV arrangement? Make a small extension so you can spread out the furniture and add some extra features. The market is full of clever ideas for making maximum use of spaces of every structure and size.

Add more windows, shelving and smart storage. Think about giving the room more character and interesting dimensions with a feature wall or unique curtains. An extension can also make improvements to the overall feel of the space, including better insulation and soundproofing. Build yourself a living area you can really feel relaxed and comfortable in.

Conservatory or garden room

Give your household some extra luxury with a fun little room you can escape into. It can be as simple or high-end as you want, but a smaller project cuts down on the overall expense this kind of home improvement can lead to. The difference in price mostly comes down to the size and construction details.

For example, would you rather have a solid or glazed roof? Each choice comes with its own set of requirements, benefits and costs. A room with plenty of glass – windows and bi-fold doors – lets in loads of light and creates a positive atmosphere. But a glazed extension should factor insulation and soundproofing into its construction to avoid discomfort and steep running costs.


If there’s a space in almost every UK home that holds great but often inaccessible potential, it’s the loft. Because of its location, the cost of a loft extension can soar, requiring changes to the roof, ceiling and related features. A staircase would also need to be installed, as well as furniture, storage solutions and anything else you want. The loft’s initial condition determines the extent of work and budget necessary to make the space liveable.

The best first step is to assess whether it’s even worth to make this kind of investment. On a practical level, are flaws in the loft’s structure adding to your bills anyway? Then think about what alterations you and the space would benefit from most. Finally, explore the market for ideas, materials and quotes to calculate a realistic budget. If you can afford the project and it’s likely to reward you in the long run, make the effort. But always keep regulations in mind.

Stages of house extension projects

Extension design - House extension cost
Extension design – House extension cost


Just like any project you undertake, the first thing you should do is plan. Whether you’re aiming for a DIY or professionally managed approach, you need to know exactly what you’re dealing with.

Think about these important factors:

  • The size of your property – take measurements of the overall boundaries, as well as the room you want to expand or add
  • Extension plans – dimensions, structure, design and features
  • Compare these plans with building regulations and adjust them accordingly
  • What professionals you’re going to need – architects, engineers, tradespeople
  • What you can do yourself – avoid DIY jobs best left for professionals
  • Based on all the above points, a budget for the project that’s realistic and manageable

If you hire an architect, they’ll be able to take care of all the construction and plans for you. They can arrange the space properly, set measurements and boundaries, and choose materials and tradespeople. They’re not the cheapest professionals to hire, but you could select specific services you need from them and come to a fixed agreement that works for both sides.

Planning permission

It can be a hassle tackling all the building regulations, understanding permitted development rights and preparing your application for planning permission. With lots of research and valid guidance from local authorities, you could take care of this part of the process yourself. But, once again, a professional would greatly speed up this essential stage and ensure you have the right information. Remember different home extension projects may have different requirements.

Groundworks and foundation

This is another job for a professional to handle. It’s essential that the extension and, so, its foundation is set exactly as specified to the local planning authorities. But getting it right isn’t just about following regulations. A bad construction can seriously undermine the integrity of the house.

What goes into building the house’s groundworks? Here are a few points:

  • Clearing the terrain of vegetation and rocks as best as possible
  • Foundation type – based on cement, bricks and other building materials
  • Foundation depth – different terrain may need deeper or shallower concrete levels
  • Applying the cement – choosing a wheelbarrow or ready-mix lorry affects the speed and cost of the process
  • Helping the cement settle into place – typically involves raking and levelling it with a length of wood
  • Planning important systems like drainage


The next step in the construction involves putting up the extension’s main structure. Depending on what you’ve chosen – masonry or timber frame, single-storey or two-storey, roof and room design – the shell will take a certain amount of time, work and money to be completed. You’ll get better results if you hire an architect and a handful of other reliable professionals. However, you should still supervise the process and make sure everything is going according to plan.


This is the stage where doors, sockets, radiators and the like are fitted. The cost of these depends on how basic, high-end or complex they are. Some common products are simple enough to set in place, whereas others may be harder to acquire, let alone install. This complicates the process, pushing your timeframes and expenses beyond what you expected. When planning the extension consider complications like these before committing to a purchase you may regret later.


From here, it’s all about interior design. DIY can really make a difference to your budget at this stage. You can easily buy appliances that only need a socket and no professional fitting. You could also learn how to fit tiles and make nifty mirrors and ornaments. But new kitchens and bathrooms tend to need the experience of tradespeople for transportation and installation, for example. If you have a clear idea of what you want for the new space, you should be able to work out who should do what when the time comes.

Who should do the house extension?

While big DIY home improvement projects are entirely manageable, they’re very complicated and require extensive knowledge and preparation. The house extension cost may be lower than if you hire professionals, but without good preparation many things could easily go wrong. Simply asking for advice from a pro would greatly improve your chances of doing a quality job.

Assisted DIY

If you’re confident in your management and building development skills, then you could combine DIY with tradespeople – one or two essential ones will do. Areas like electrics and planning permission could use the backing of an expert. A dedicated team of friends and family can contribute to different stages of the construction. With patience and a lot more care, a single-storey extension could pan out without a major hitch.

Various professionals

For more complicated projects, however, you should invest in a lead engineer and a few minor tradespeople at the very least. The cost may be greater than DIY, but you can be sure to get a well-constructed building in the end. Dependable professionals also come with health and safety measures, including specific polices, scaffolding, protective gear and insurance, that make work less prone to accidents.


The best service to put your money on is a vetted architect, either ARB or CIAT certified. The key advantage is that one highly organised person can oversee every part of the process. Whether an independent professional or whole firm, services can include planning, constructing and managing the extension from start to finish. But, don’t worry! Your voice is still essential to making decisions and supervising procedures.

The downside is, of course, the price. Ask any homeowner who’s hired such a professional before: how much does an architect cost? The answer is not a simple or an entirely pleasing one. Firstly, they usually charge a percentage of the overall construction cost, but may offer the option of a fixed lump sum or hourly rate. Generally, a simple survey could be a couple hundred pounds. But, for a bundle of quality architectural services, expect to spend around £2,000 – £3,000 – if not more!

Take a look at this basic price guide of different services you may need for a house extension:

Job type Average cost
Architect £500 – £3,000+
Engineer £500 – £2,000+
Electrician £1,000 – £6,500+
Plasterer £500 – £1,000+
Plumber £1,000 – £2,000+
Builder £5,000 – £10,000+
Decorator £500 – £2,000+

How long does a house extension take?

Conservatory - House extension cost
Conservatory – House extension cost

The timeframe of a whole project is, of course, made of the different stages in the process. Your choice of materials, designs, professionals and so on directly affect how complicated and long each part will be. A minor single-storey side extension could take a week or two. Anything more intricate and you should prepare for around 12 weeks of disruption – for you and your neighbours. So make arrangements well ahead of time, for alternative accommodation

How much does a house extension cost in 2021?

There are a number of house extensions you could opt for, deciding on the right size for your home and garden. Here are some of the country’s average house extension prices:

Extension size Average cost
Single storey £1,500 – £2,400 per m2
Two storey £1,500 – £3,000 per m2
Extension location Average cost
Side £30,000
Rear £35,000
Wrapped £55,000
Extension feature Average cost
Masonry £180 per m2
Timber frame £1,200 per m2
Flooring £25 – £100 per m2
Bifold doors £2,500 – £7,000
Sliding doors £500 – £4,000
Central heating £3,000 – £4,000
Underfloor heating £2,000 – £10,000
Boiler £500 – £10,000
Glass £20,000 – £80,000
Extension type Average cost
Bathroom £5,000 – £10,000
Kitchen £5,000 – £20,000
Conservatory £6,000 – £20,000
Loft £20,000 – £40,000

Be aware the price guide above is only intended as a reference point. If you’re considering a house extension then make sure to compare up to four house extension quotes with Quotatis’ quick and easy service.

Extra expenses

The final cost of the overall project can include several additional expenses you didn’t predict, so it’s a good idea to set a budget that’s prepared for this. Something as simple as the soil of your property not being in ideal condition for construction could up the labour cost. Keep a checklist of different factors that can affect the work and price of your tradespeople.

Reason for extension

The extension’s purpose is, of course, key to what materials and methods will be used. These affect the timeframe and necessary expenses. For example, a bathroom will need all sorts of piping and heating systems installed. If you’re building one from scratch and not revamping an existing one, the process will take extra time and work.

Special features

If you have glass features, going for double and triple-glazing is a wise move to keep your home well-insulated and cosy. Prices can soar, however, because of the quality windows themselves, as well as their installation and maintenance. Browse different retailers and independent services before settling on the best deal for your budget and circumstances.

Extension size

The size of the extension is also vital to the scope of your expenses, whether standard or extra. First off, extensive plans will require a visit to your local authority for planning permission, which costs £206 minimum. On top of that, in the case of a loft conversion, for example, that’s close to regulation limits, you may need to resort to smart solutions to make the space work – their construction can be an added expense.

Location of extension

Your property’s location is just as important to building regulations as much as construction methods. To begin with, development on conservation areas, national parks, world heritage sites and other significant locales needs special permission, measures and costs. At the same time, an overly cold or wet climate generally means the soil may be too hard or muddy to build properly.


Sometimes a simple extension becomes a lot more expensive because essential systems and metres need to be moved or altered. You need a licensed professional to carry out this work, which also means walls are going to be damaged and plastered. The last part alone can cost you somewhere between £400 and £700.

Length of work

The project’s timeframe affects the upfront quotes you’ll receive from tradespeople. If that’s dragged out for some reason, that initial cost can expand to account for the extra labour. Take measures to ensure the process stays on track, such as making sure workers have easy access to the site and ordering materials ahead of time.

VAT is another common burden for builders and customers. When asking around for quotes, check how much VAT takes up each professional’s price. Keep in mind that self-employed tradespeople and second-hand materials can come with minor or even zero VAT. But don’t undercut the value of experienced and well-vetted support.

How to set a realistic house extension budget?

Careful budgeting - House extension cost
Careful budgeting – House extension cost

The sheer number of influencing factors in construction makes it very important to prepare for the possibility of something going wrong and costing you extra. Apart from the basic quote your professional has set, you need to expand your funds to cover additional expenses that may turn up.

There are a few things you can do to calculate a suitable and realistic budget:

  • Don’t go for a design that’s more complicated than you actually need
  • Make a detailed plan for your project – include measurements and features
  • Get accurate quotes from tradespeople, which detail VAT and the estimated cost of extra elements
  • Avoid expensive options – reserve costly elements or services for a few specific parts, like finishes and door handles
  • Go for off-the-shelf instead of custom-made products
  • See what parts of the project can be done the safe DIY way

Financial assistance

Your home insurance provider may cover some or all the cost of an extension. But the project would have to be due to specific forms of damage, like that caused by weather or a burglary. Check the terms and conditions of your existing insurance. If you don’t have any and you’re thinking of changing that, focus on researching what’s on offer in terms of home extension assistance.

There are also self-build structural warranties that can help with the house extension cost without getting involved with home insurances. Most quality construction services will offer this service at an extra expense. Whether you choose them or an independent provider, a warranty means the construction process will be surveyed for defects during development and typically ten years after completion. Any repairs are covered, protecting your deposit and health.

Grants or loans from local authorities are another route you could take for home improvements. Get in touch with your council and find out what they can help with. There may be requirements you need to meet in order to be eligible. But, if all goes well, you could get additional funds for cheap materials, labour, surveys and more.

Building regulations and suggestions

There are several rules you should follow, some officially sanctioned and others generally considered good practice. If you have neighbours, for example, it’s essential that you get a Party Wall Agreement waiver set up and signed at least two months before construction starts. This ensures neighbours are aware and okay with any alterations, whether to boundaries, walls or groundwork.

When it comes to building regulations, research the exact limitations to your particular project. Standard restrictions include:

  • Features like balconies or chimneys don’t count as extensions
  • Conservatories can’t face a highway
  • Materials used must be the same or similar to the original property
  • The extension and additional buildings can’t take up more than half the overall property
  • It also can’t exceed three to four metres in height or the peak of the roof
  • A single storey rear extension can’t be more than three metres in length for an attached property or four metres for a detached property.

Narrow down the specifications of your project. Then make a list of the planning permission regulations you and your hired professionals have to stick to while expanding the house. This way you won’t end up needing expensive alterations alongside everything else included in the average cost of house extensions.


Hopefully, our guide has filled you in on the many aspects you’ll encounter when organising a home extension project. Create a detailed outline of desired features, as well as who the best person is to carry them out and how much they’re going to cost. It’s important to be patient and smart about your choices without letting this complex and often busy market overwhelm you.

If you’re ready to start looking for tradespeople or just need some extra advice, don’t hesitate to fill in our form below. You’ll get up to four quotes from a range of professionals with the experience and credentials to help.

Electra Nanou

Electra Nanou is a Content Marketing Intern at Quotatis. She writes a range of digital content related to products and services, while striving to make every online experience as pleasant and helpful as possible.