House extensions from £20,000 to £30,000: what can you build with your budget?

An extension is a great way to add more space to your home, but just how far will a budget of £20,000 to £30,000 stretch? Renovation expert Michael Holmes looks at what's possible

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Extending a house for between £20,000 and £30,000? Making the most of your existing property by extending for under £30,000 can make a lot more financial sense than selling up and moving on. And you can still add significant value, even in the current climate – if you choose the right project. 

Thinking about extending a house to make more space? There are worthwhile improvements you can make to your house for a lot less than £20,000, of course, but if you can raise a budget in this range, you could convert a modest loft, convert a single garage into a living room or add a small extension or conservatory, even build a garden room. So, what are the options open to you in your budget range?

How much does an extension cost?

Use our extension cost calculator to accurately budget for your house extension. For a rough idea if you are planning, designing and costing a cheap 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.

What kind of extension can you build for £20,000 to £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. Consider these extension types, which can all fall within the £20,000 to £30,000 extension cost range:

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, possibly with a small en suite shower room.

A guest bedroom in a converted loft with a white and grey colour scheme

(Image: © 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.

Above-garage extensions

Building an extension over a garage that's already there 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 regs would apply, of course.

Home office in living room by Ikea

(Image: © Ikea)

Converting a 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.

Single-storey side or rear extensions

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 back 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.

A budget of £20,000–£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.


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. 

Adding a conservatory or orangery

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. 


(Image: © 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.

Building 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: © 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.

Read more about extensions