House extension: how to budget for yours plus 22 achievable designs

Whatever your budget may be, your house extension can be a success. Take a look at these home extension projects for inspiration and max out your home's potential

House extensions for every budget: Single storey kitchen extension by Studio Mesh
(Image credit: Adam Woodward)

Contrary to popular belief, beautiful house extensions can achieved, on every type of budget. So if you're thinking of extending, it's worth doing some research and evaluating your options. Whether you're considering adding an orangery or a simple rear home extension, there are ways to achieve your desired results and use your home's full potential, while sticking to your available budget.

Want to build an extension for £20,000? We've got achievable suggestions for that, and much more. Whether your budget is £30,000, £50,000, or something in-between, we have plenty of innovative ways to make that house extension happen, in a way that suits your financial situation. And if you have much, much more to spend, we can show you how to add value to your home with an extension of a larger footprint too. 

Before making plans, – whether a rear extension for a bungalow, a single storey extension for a 1930s semi, a loft extension on a terraced house, or an expansive double storey extension, – this feature will give you an idea of what can be done with the money you have available.

We've delved into the detail to prove how a well thought out home extension can be affordable, and still add significant value to your property, even in the current climate. You just need to choose the right project.

Find out more about extending a house in our ultimate guide.

How much does a house extension cost?

Our extension cost calculator will help you accurately budget for your house extension, but, as a rough guide if you are planning a single storey extension, expect to pay (for building work only): 

  • Around £1,500 to £1,900 per square metre for basic quality; 
  • From £1,900 to £2,200 per square metre for good quality; 
  • Between £2,200 and £2,400 per square metre for excellent quality.

Don't forget that where you live will affect the cost of your home extension, too, with big cities generally more expensive to extend within than elsewhere due to increased labour costs. You can keep costs down by doing some of the work yourself, such as the project management. Find out how to project manage an extension or renovation in our guide.

House extensions for every budget between £20,000 and £30,000

Some types of extension are cheaper than others – although what you choose needs to suit not just your budget but your needs, too. These fall into the category of house extensions for every budget between £20,000 to £30,000:

1. A simple room-in-roof loft conversion 

Loft conversions in a typical 89m² three-bedroom terraced house would cost from around £1,000 per m², depending on where you live. This will create a new room measuring 22 to 28m². This is enough space for a good-sized double bedroom extension, possibly with a small en suite shower room.

House extensions for every budget between £20,000 and £30,000: a guest bedroom in a converted loft with a white and grey colour scheme

(Image credit: Jeremy Phillips)

Such a project would likely be covered by permitted development rights and so would not require planning permission, though the work would have to comply with building regulations. This is a job for a building contractor or specialist design-and-build loft company. Find out more about planning and designing a loft conversion in our guide. Discover how to plan an en suite bathroom in our dedicated guide, too.

2. An above-garage room extension

House extensions for every budget between £20,000 and £30,000 can include building an extension over a garage that's already there. It is more cost-effective than building a new ground-floor extension, providing the existing foundations can take the load (an engineer or surveyor can advise).

You’ll also need a designer and contractor. An added bonus is that no garden space is sacrificed, but in most instances you will require planning permission from your local planning department, with the application fee costing £172. A 17m² extension above a typical attached single garage would cost £900 to £1,500 per m². Building regulations would apply, of course.

Home office in living room by Ikea

(Image credit: Ikea)

3. A conversion of an integral garage

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If you don't have the budget to create the extension you want, a more cost-efficient way to get the rooms you need is to look at reworking the space you have. 

If you rarely use your garage and parking isn't at a premium where you live, it may be worth creating another habitable room by converting your garage. 

You can expect to pay between £5,000 and £7,000 upwards (depending on spec); that's around £1,000 to £1,250 per square metre – if the walls and floor are stable, there is a watertight roof, and the ceiling height is sufficient to leave around 2.2m to 2.4m of headroom after building up the floor by 15cm above external ground level. 

Design fees for a garage conversion range from £1,200 to £2,500, plus £300 to £400 for a structural engineer. A typical single garage conversion (18 square metres) would cost around £17,100 to £23,900 plus VAT, depending on specifications.

If the structure is attached to the house, rather than integral, and needs structural repairs, it may be more cost-effective to demolish and replace it.

Find out more about garage conversions – from planning to design in our ultimate guide.

House extensions for every budget between £20,000 and £30,000: Living space overlooking staircase and kitchen for garage conversion ideas: by Stephen Graver Architects

This former garage has been converted into a living space and knocked through to the main house to create a large, open plan kitchen, living and dining space. See more of this room in our garage conversion ideas gallery. Architect, Stephen Graver

(Image credit: Marc Wilson Photography)

4. A single-storey side or small rear extension

A single storey extension is the perfect way to create extra living space in your home, while transforming your space to better suit your lifestyle. Whether you're considering a side return extension (read our guide to find out more) or a rear extension, it's the perfect spot for a new, open plan living, kitchen and dining area that make for perfect family spaces and, of course, are so beloved by potential future buyers.


This contemporary sun room by Crichton Wood Architects replaced Anne and Jim Gilchrist's old scullery and coal bunker. The couple could have achieved more space with their £22,000 budget by choosing a classic timber-and-glass conservatory, but love the resulting high-quality, individually designed space, which is integral to their house. 

House extensions, for every budget between £20,000 and £30,000 would only be sufficient to build a new single storey extension of around 20m², at a cost of £1,050–£1,450 per m². This would be sufficient space to extend an existing room, or to add a good-sized home office or utility room to your house. Most such extensions would be covered by your permitted development rights. Find out how to add a rear extension under permitted development. Discover all you need to know about planning, designing and costing a single storey extension, too.

5. A conservatory or orangery house extension

Conservatories and orangeries come in all guises, from period-style to more contemporary builds, and the more affordable end of the market is well within the reach of someone with a budget of up to £30,000. 

House extensions for every budget between £20,000 and £30,000: a conservatory

(Image credit: Brett Charles)

Most people will hire a conservatory or orangery design and build company for ease, but you can do it on a DIY basis to save money.

DIY conservatories can cost as little as £3,000, and come in a range of standard designs, ready for installation by you or your builder. Bespoke conservatory or orangery companies offer tailor-made designs, with lower to mid range styles costing from £10,000 to £15,000. Find out how to plan a conservatory and how to add an orangery, too.

6. A garden room

Building a garden room is a great solution if you need more space but have no room for an extension near the house. A room in the garden might solve all your space problems, be it a home office or cinema room. You could also use it as a home gym, hobby room or children’s playroom. Or maybe it’s for outdoor dining when the weather’s cooler, or a sheltered spot to enjoy the garden from?

Cedar garden room with outdoor deck surrounded by planting

(Image credit: RHS/Neil Hepworth)

Garden room costs vary according to their size; whether they are modular or bespoke; the quality of the materials used; the doors and windows specified; the level of insulation required; and the interior and exterior finishes.

For a modular kit, expect to pay anywhere between £2,000 and £30,000. For a completely bespoke building, expect to pay between £800 and £1,600 per square metre. Find out more about building a garden room in our guide.

House extensions between £30,000 and £50,000

This will comfortably allow you to create a substantial house extensions including loft conversions, garage conversions or basement conversions, large single-storey extensions and even a modest two-storey extension. Here, we also show great examples of house extensions for every budget between £30,000 and £50,000.

7. A larger, orangery-style rear extension

A traditional-style house extension option, an orangery is designed to be in keeping with a period house and measuring 30m², would cost between £1,250 and £1,450 per m² depending on location. A room measuring 4m x 7m would be ideal for a dining or sitting room and, in many instances, would fall within permitted development rights and so not require planning permission. Find out how to plan and design an orangery in our guide.

House extensions for every budget between £30,000 and £50,000: traditional conservatory from David Salisbury

The owners of this Somerset house required both extra living space and a small dining area. They chose to extend with a conservatory from David Salisbury which would create a light-filled room to suit their property. It cost around £40,000

8. A loft conversion with bedroom and bathroom space

As well as offering valuable extra living space, loft conversions give one of the best returns on investment you can get when it comes to extending. 

And because most loft conversions are generally allowed under permitted development rights, there’s no need to go through the lengthy process of obtaining planning permission.

The cost will vary depending on size, but you can expect to achieve this type of house extension for every budget between £30,000 and £50,000. A typical conversion with a rear dormer in a mid-terrace property costs around £35,000. You’ll find small companies will usually charge 10 to 15 per cent less than large companies. Find out more about planning and designing a loft conversion in our guide.

terraced house with large side extension and box dormer

(Image credit: Alison Hammond)

9. A double garage conversion for expansive living space

An attached double garage measuring 28m² could be turned into extra living space at a basic cost of £850 to £1,050 per m². To then integrate this space into the existing house by removing the partition wall – replacing it with an RSJ – add around £5,000 to the cost.

House extensions for every budget between £30,000 and £50,000: a single storey side extension to the front of a Victorian property

A single-extension was added to the front of this Victorian home in Surrey. Reclaimed bricks were sourced to match the original brickworks and bargeboards made to replicate the existing exterior. This project cost around £46,500 for materials and construction

If the space were to become a new kitchen, the cost of new units must also be added at around £5,000 upwards, depending on the kitchen supplier chosen. Your permitted development rights mean a garage conversion will not usually require planning permission, but it must comply with building regulations as the project would constitute a material change of use. Read more in our beginner's guide to garage conversions.

10. A cellar conversion for added living space

An existing cellar measuring around 35m² could be converted into an additional living room or home office at a cost of around £850-£1,050 per m², including damp proofing (a tanking membrane) and insulation.

Adding a new lightwell and window would cost an additional £4,000-£5,000. Cellar conversions come under permitted development rights but, as above, this is a material change of use. For details of specialist cellar-conversion firms, try Find out how to convert a basement or cellar.

dark grey living room in a Victorian home

(Image credit: Matt Gibbs)

11. A side return extension to expand a kitchen

A side return extension is a good way to incorporate often unused or under-used garden space into your home, creating a much larger, open-plan room that's ideal as a kitchen diner living space combined. This type of extension is also the perfect opportunity to bring more light into what is usually a terraced house, with large rooflights, panels of glazing and French, bi-fold or sliding doors creating a bright, contemporary home. 

Budget for £1,050 to £1,450 per m², although bear in mind that large expanses of glazing will bump up the cost significantly. Find out more about planning a side return extension in our guide.

Sarah Brooks glass box extension has transformed the kitchen in her London home

(Image credit: Malcolm Menzies)

12. A small double storey rear extension

This level of outlay could be sufficient to create a substantial single storey house extension, 30m² to 40m² – budget for £1,050 to £1,450 per m². 

This might be enough to extend by around 4m right across the back of a typical semi or detached house, with either a flat or low-pitched sloping roof – as a single storey or side return extension, both ideal for creating a large open-plan kitchen-diner.

A contemporary design with folding-sliding doors, glazed roof lanterns and large floor-to-ceiling glazing units would cost £1,800 to £2,200 per m², so on the same budget, the scale of the space may need to be reduced to around 23m². 

Many single storey side extensions and rear extensions will fall within your permitted development rights, which will help keep costs down somewhat, but always check. And building regulations will apply. Don't forget to add on professional fees, and to calculate interior fit out costs carefully. Find out more about planning, designing and costing a single storey extension in our guide.

House extensions for every budget between £30,000 and £50,000: IQ glass contemporary black extension

HUT architects designed this extension to a family home in London with the help of IQ Glass. The owners wanted a minimal extension with plenty of personality, that would maximise light and space. A dramatic double-height box on one side draws light up the staircase. It cost £36,000 for the design and installation

13. An expansive double storey house extension

More cost-effective than a single storey house extension because it doubles up on the use of the foundations and roof – two of the most expensive parts of a build – a two-storey extension on this budget could measure up to 30-40m² (both floors). At the rear of a property, this would typically extend the kitchen with a new bedroom above.

Many such extensions projecting no more than 4m from the rear of the original house are covered by permitted development rights, but a two-storey side extension will require planning consent – and don’t forget building regs. Find out all you need to know about adding a double storey extension in our guide.

Arboreta glazed oak and stone two storey extension

The owners of this stone-built farmhouse, which is located in a small town between Carmarthen and Lampeter, in west Wales, tasked oak frame design-and-build specialist Arboreta with creating more space. The extension was designed to take in views with a sunroom downstairs and bedroom above. Lots of glazing was incorporated while maintaining a look that was sympathetic to the period style of the home. A similar oak-framed extension would cost around £35,000 from Arboreta

14. An extension for a bungalow to make it family-sized

Whether you're looking to extend a bungalow or want to join two distinct buildings together, – perhaps the original house and a garage conversion – a glazed walkway can be a very successful and cost-effective way to do so. Whether your home is modern or traditional, a glazed walkway can be a great solution to planning restrictions on period properties, or homes within conservation areas – a listed building for example –, where a solid link would be inappropriate or not permitted.

House extensions for every budget between £30,000 and £50,000: extending a bungalow by putting a glazed addition between two solid wall extensions

(Image credit: Brent Darby)


Single storey kitchen extension at the back of a house

(Image credit: Adam Woodward)

Using basic building materials is a great way to keep costs low and if you can do some of the work yourself, all the better. That doesn’t mean placing limits on the design, though. The striking exposed scissor truss timber roof of this brick extension, which was built by hand on site using standard materials, is topped with a green sedum roof. 

Architect Henry Smith of Studio Mesh and his brother Alec took on most of the construction work themselves when extending a one bedroom flat in an early 1900s dairy cottage into a 77sq m two bedroom flat for just £39,500.

Single storey kitchen extension by Studio Mesh

(Image credit: Adam Woodward)

House extensions for every budget from £50,000 to £90,000

With more money, you could achieve larger scale extensions, such as double storey additions, or you could take on a unique build to totally transform your home life. Perhaps a large loft conversion, a kitchen extension, a stand-out glazed extension or a basement conversion. Here, we take you through house extensions for every budget between £50,000 and £90,000:

16. A kitchen extension with space for lounging too

Building a kitchen extension is the perfect opportunity to improve the entire ground floor of your home, with a simple change of layout, the introduction of natural light and the addition of appliances that could make your life easier. Plus you can expect this type to fit into the house extensions for every budget between £50,000 and £90,000 category in many parts of the country, with the exception, potentially of London.

If you have the space, plan to create an enhanced room that doesn't just including kitchen and dining areas, but zone for lounging, too. It's also really worth maximising the connection of the new room to the garden with bi-fold, sliding or French doors. 

Prices will vary depending on the work you carry out, but as a guide, plan for between £1,200 to £3,000 per m² and upwards for building work; £17 to £200 per m² for a new kitchen. Find out more about kitchen extension costs in our dedicated feature. And discover all you need to know about building a kitchen extension in our guide.

a bright and light-filled kitchen extension with kitchen island

(Image credit: Philip Lauterbach -

17. A large loft extension to expand your bedroom count

Extending the loft on a large semi-detached house and converting the existing roof space will cost £850 to £1,450 per m² and, at this budget level, you could add two good-sized bedrooms and a bathroom, or one very generous master suite with dressing and shower rooms. 

In England, quite substantial loft conversions are still covered by permitted development rights. Larger conversions and those involving the addition of a window facing the highway will require planning consent. Building regs apply to all work. Use our guide to converting a loft to find out about all the practicalities involved.

House extensions for every budget between £50,000 and £90,000: a master bedroom in converted loft

(Image credit: Brent Darby)

18. A value-adding double storey side or rear extension

Two storey side or rear extensions are more cost-effective than single storey extensions, coming in at around £1,320 to £1,620 per m² for a standard build, so with this budget you could extend by at least 35m² – sufficient space to add a large kitchen and/or living room extension on the ground floor, with two new bedrooms and a bathroom above. 

A large two storey extension is likely to require a planning application, so approach your local authority about this and for its advice on building regs. Find out more about planning, designing and costing a double storey extension in our guide.

Zinc clad glass box side extension

(Image credit: Des Ewing Residential Architects)

19. A large side return extension

A side return extension is a classic way to enlarge a Victorian/Edwardian semi-detached or terraced house; some of these extensions go straight out to the side, across the full width of the property, filling in the alley alongside the kitchen; others go sideways and outwards; where space is available, side return extensions can even be combined with a second-storey extension above the original kitchen, creating an additional bedroom. 

The trick to creating a successful side return extension is to find a balance between enhancing the internal space without sacrificing too much garden. It's also important to ensure that the house doesn't become unbalanced, with a large living area downstairs but few bedrooms upstairs. For this reason, it's worth considering a side return extension in conjunction with a loft extension.

A side return extension with an open plan kitchen diner

(Image credit: Tim Mitchell)

This type of build involves opening up both the original rear and side walls of the kitchen at the back of the house, inserting steel beams so the new and old spaces become one. Such a project may also involve adding a small downstairs cloakroom/utility room and diverting the existing drains with the addition of a new inspection chamber in the garden. 

While a single storey may come under permitted development rights in England, extending on two storeys and right up to the boundary is likely to require planning permission wherever you live. As usual, remember that building regs must be observed. Find out more about planning a side return extension in our guide.

20. A glazed extension

If you're looking at house extensions for every budget between £50,000 and £90,000, you might like to consider a glass extension. This extension type can look very impressive and can work with any style of building, including period homes, but can cost £3,000 to £4,000 per m². A large budget should be sufficient to pay for an extension measuring 15 to 20m², however, enough for a small dining or living room at the back or side of a property. Because of the specialist engineering involved, it is perhaps best to hire a specialist design-and-build firm – try GlasSpace or IQ Glass. They will handle building regs; a small extension is unlikely to require planning consent. Find out more about planning a glass extension in our guide.

luxurious glass box kitchen extension with frameless glazing

(Image credit: Gregory Phillips Architects)

21. An expansive basement conversion

Converting a basement is just about the most expensive way to extend, but in a high-value area and with all other options exhausted, it may be the best option. At a typical cost of £3,000 to £4,000 per m² including light wells, even such a large budget will not go very far, creating perhaps a 15 to 20m² basement – ideal for a home office or cinema room

For a design-and-build firm, try Orbital Basements or The London Basement Company. For information on cellar conversions and basement extensions in general, contact The Basement Information Centre. Find out more about converting a basement in our guide.

kitchen diner and living space in a basement extension to a Victorian home with a golden retriever

(Image credit: Simon Maxwell)

22. A kitchen and bathroom extension

A unique extension could meet all your needs for extra space. In this case the challenge for architects Office S&M was to come up with a plan for a terraced house in North East London with a kitchen and bathroom, each overlooking the garden. They made best use of the restricted space by splitting the £90,000 extension diagonally with a storage wall, creating two angled rooms. The side with a circular opening contains the bathroom and the black-framed doors lead to the kitchen. ESW completed the extension in Prokol polyuria, a spray-on coating which was first developed for oil rigs.

unique terraced house extension

(Image credit: French + Tye)

Need more extension advice and inspiration?