Cut extension costs: 23 ways to reduce costs and extend a house cheaply

There are ways you can cut extension costs if you want to extend a house cheaply. Planning an autumn extension now? Use this expert guide to find out how to extend on a budget

Cut extension costs: Extension by Plus Rooms
(Image credit: Plus Rooms)

If you want to cut extension costs or simply extend your house as cheaply as possible, it might be time to rethink your plans and extension design rather than your budget. There might be ways to shave a bit of money off various elements of your extension project – from being clever with the design to cutting the cost of labour – without ruining the look or function of the space.

Summer is the perfect time to plan an extension, so that you can get the quotes in over autumn, ready to go for spring. Use these tips to find out how to save money on the cost of an extension and extend a house cheaply – but still get a great result. Find out more about extending a house in our ultimate guide, and use our extension cost calculator to work out your project's budget.

1. Do your sums then cut extension costs

Save money by extending at the best time of year

Timing your extension for good weather is one of the simplest ways to cut extension costs. Why? Because bad weather causes delays, which can mean increased labour costs, rejigged schedules and, if you're renting while you extend, increased rental accommodation costs, too. 

Weather damage from the wind and rain can up your costs, too, and what started as a simple loft extension can become a complete redecoration job for all the bedrooms below if rain penetrates tarpaulins.

When to extend? Try to line yours up for when you know there tend to be prolonged periods of dry weather where you live. Avoid weeks when frost is an issue, too.

Before you consider what you need to trim off your extension budget, work out exactly how much you need to spend to get the extension, including the interior fit out costs, you want. Then, when you're happy it can be achieved, go to a trusted local estate agent and ask how much your home might increase in value with your proposed project in place. Ideally, your extension should add more £££s to your home's value than it cost. Bear in mind that larger extensions will be more cost-effective than small extensions but will, of course, cost more, and could push your home past the ceiling value of the street. The importance of balance when it comes to budget versus profit potential can't be exaggerated. 

Find small extension ideas and advice in our guide.

Cut extension costs: a large white kitchen extension with contemporary finish by mulroy architects

(Image credit: Joakim Boren (Mulroy Architects))

2. Cut the cost of an extension with a simple design

Curves and corners are costly to build, so keep your extension design as simple as possible. Building a house with a rectangular or square footprint with a simple pitched roof is the best way to cut extension costs or to extend a house cheaply in the first place – without compromising on the build's quality. 

Use our guide to building a single storey extension for design tips.

Cut extension costs: conservatory style extension on a victorian house

3. Plan ahead in detail to extend a house cheaply

Spending time planning the smallest of details can save you money and cut extension costs further down the line. By specifying everything from light fittings and socket locations to flooring and wall colours at the outset, you’ll save money on the cost of making alterations or snap decisions at a later stage.

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4. Stick to the agreed design to cut extension costs

Then, it's important to stick to the agreed design if you want to keep the budget down.

‘It’s important to stick to the plan and design you’ve agreed, as any changes will cost money,’ says surveyor Steven Way. ‘Have a proper building contract with an itemised budget and an order of works in place, which will help save you money in the long run.’

Use our guide to extending for under £50,000 for more budget-friendly tips.

5. Go off-the-shelf not made-to-order to extend cheaply

Design the build around off-the-shelf products, such as standard-size doors and windows. Avoid any products that have to be made to order; instead, choose materials that are readily available and easy to use. So, stick to cast concrete for the sub-floor; concrete blockwork for the walls; brick, render or timber cladding; and a softwood timber roof structure. Try rooflights instead of dormer windows and interlocking concrete tiles for covering the roof.

Related articles: Permitted development rights for extensions | Kitchen extensions all under £100k | House extensions for every budget

6. Cut extension costs by avoiding complicated groundworks

If possible, avoid complicated groundworks, such as building near to trees or drains and sewers, or other buried services, as these will increase groundwork costs. Remember, though, that if you live in a period or character property, your choices will be limited.

Read more: Maximise natural light with a glass box extension 

Cut extension costs: infographic of ways to cut the cost of your extension

7. Project manage yourself to save on the cost of an extension

A builder will add 15 to 25 per cent on to the total cost of labour and materials to cover their time for managing the project. You can save some of this cost by effectively taking on the role of building contractor yourself. This will mean liaising with your designer/architect and your local authority’s building control department, finding and hiring tradespeople, directing the work and supplying all of the necessary materials, plus scaffolding, skips and so on.

Though time-consuming, it can be very rewarding. To do it well, you need time and flexibility, plus confidence, management skills and some knowledge of construction. The job may take longer to complete overall, but the savings can be enormous. Find out how to be a good project manager in our guide.

8. Get the timings right to keep down the cost of an extension

Whether you're project managing or just ordering your own materials to save money, getting the timings of deliveries right to save on wasted labour costs is vital. 'A site with no one working on it is costly, so materials need to arrive in plenty of time,’ advises Steven Way, practice principal at Collier Stevens Chartered Surveyors.

9. Save on VAT to cut back on extension labour costs

Most extension work will attract VAT at 20 per cent on labour and materials, but if you use self-employed tradespeople who each turnover less than the threshold for VAT registration, you will not be charged this tax — saving on labour costs. Second hand materials sold by private individuals on the internet will also be free of VAT.

Some types of work attract reduced-rate VAT at in any case — upgrading insulation and extending a building that’s been empty for two years, for example.

Find out how to reclaim VAT on your building project.

10. Get next door to sign a party wall agreement waiver 

If you are building on or near the boundary of a neighbour, your extension will need to comply with the party wall act. If a party wall settlement is required, it will cost around £700 per neighbour; more if they use their own independent surveyors, which they're within their rights to do, and for which you foot the bill.

You must notify your neighbours in writing about your extension plans eight weeks before you start. If you can get them to write back that they do not object or complete a party wall agreement waiver, you can avoid using a surveyor to arrange a party wall settlement and save on fees.

It pays, therefore, to keep neighbours on board with your project, discussing plans and being considerate about any concerns they have.

11. Save on extension planning fees and costs

While it is a false economy not to invest in design, some designers know how to keep down costs, while others only produce very complicated, if beautiful, plans that are very expensive to build. For a simple, low-cost build, find an architect, architectural technician, chartered surveyor or structural engineer who will produce planning and Building Regulations drawings for a fixed, all-in price. Look for a track record in designing low-cost projects.

If your extension can be designed to fall within your permitted development rights (see www.planningportal.gov.uk), no planning application will be required. This will save the planning fee of £206. Find out if your project needs planning permission in our guide.

12. Comply with building regulations to reduce extension costs

Building regulations are often confused with planning permission but they are distinctly different and even if you're building under permitted development, you must comply with them. Doing so means paying building control fees, which you can't avoid. What you can avoid, however, is the cost that will be heaped upon you if you ignore the rules and are made to undo and redo the work correctly at your own expense by your local building control department. A good builder will always be on top of this but do spend time checking yourself – and ensure all the paperwork is signed off at the right stages of the job. The buck stops with you. 

13. Avoid cowboy builders if you're extending a house cheaply

There are plenty of cowboy builders (as in any trade) and they may vastly underestimate costs — through incompetence or, possibly, deliberately to secure a job. They may then ask for more money for changes or extras. They could even demand some or all of the money up front, leaving you with no comeback if they fail to complete the work to satisfactorily.

To avoid being ripped off, always ask for references — and check them. Never, ever pay for building work in advance; pay only for work that has been completed and that you are happy with.

For a small project, pay when the job is finished. For an extension, agree payments at set stages, or interim payments based on a verifiable list of labour and materials used up to date. Never hand over money for materials in advance. If a builder does not want to supply materials, buy them yourself. Find out how to find a reliable builder in our guide.

14. Measure twice, but cut only once to cut extension costs

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Making changes or mistakes that waste labour and materials is a major factor in the final bill for many projects. Measuring everything on site, rather than off your plans will help reduce wastage. Having accurate, scaled plans in the first place will help.

The more time spent at the design stage, visualising the end result, the more problems can be anticipated and headed off. Accurate and complete design will ensure that you have services, such as plumbing and wiring, in the right places, get floor levels right between rooms, and ensure that doors are hung to swing in the most space-efficient direction.

Once you have made up your mind, stick to it; changes always incur extra costs, often in ways that don’t reveal themselves until much later.

Over-ordering materials can also waste money, but it’s better to have slightly too much than to fall short and have problems making up the difference. This will incur delays and extra delivery charges; worse, you may not be able to find the exact same thing again.

15. Reuse, recycle and repair to save on extension costs

Existing materials can be reused rather than thrown in a skip. Old floorboards, doors, radiators, towel rails, kitchen units etc. can all be revived and reused, cleaned up and given a new finish. 

Reducing wastage will also reduce costs for skip hire and disposal. Bear in mind, too, that as a private individual, you can dispose of waste in your local council tip for free.

16. Buy secondhand to save on extension costs

Buying salvaged materials – on the internet or from salvage yards – can be a lot cheaper than buying new. It will also introduce instant character. Second-hand items that offer good value include roof tiles, bricks, internal doors, timber floorboards, fireplaces and roll-top baths. Some people even hunt through skips - although you must ask the householder before removing their waste.

Cut extension costs: a kitchen with large pivot door and picture window, concrete-effect worktops and floor, and exposed beams in the pitched extension roof

(Image credit: Chris Snook)

17. Sell what you don't need

Can’t reuse or recycle existing materials? You'll be surprised what you can sell – from bathroom fittings to old kitchen cabinets. Advertise on local Facebook groups or Gumtree.

18. Negotiate trade discounts to extend a house cheaply

Find out where those in the trade buy their materials and aim to get the same wholesale/trade prices. Always negotiate and see if there is any discount for paying in cash – making sure you get a receipt. Bulk-buy from a single supplier for a further discount and ask about reduced delivery costs. Buying end-of-line deals will save you a fortune, especially on items such as carpets, units and appliances.

Getting the best deal will often mean moving away from the big brand names and finding equivalents without the price premium. If you are clever, however, you can save on price without compromising quality.

To keep down costs, stick with a basic specification – so go for radiator-based central heating, carpets for floors and standard white sanitaryware, for example.

rear extension with contemporary feel made from glass attached to period property by iq glass

(Image credit: IQ Glass)

19. Limit the relocation of services

When you're extending a house, consider the position of fittings, for example, a new toilet. If yours can be placed in a convenient position for the existing soil stack, you'll save on labour costs.

20. Find a problem-solving builder to cut the cost of your extension

If you want to keep costs down, it's important to find a builder with both experience and an ability to think around problems. This isn't always easy, but with good research locally, you will find a builder (or project manager) who can think on their feet. When you're comparing quotes, don't just ask about extension costs; quiz your prospective builders, too, about their experience, how they've overcome problems, whether they work with a fixed team or a shifting workforce, and whether they have access to surveyors or architects. The answers will all help inform you of their experience and abilities.

21. Visit the site regularly to keep extension costs low

Visiting the site to ensure the work is moving along well is a must during extension work. Doing so will allow you to ensure the project is moving along well, that there are no supply problems that your main contractor hasn't told you about, that the workers themselves are happy – and turning up – and that the schedule is being stuck to. There is a caveat if you're looking to cut the cost of an extension: don't use these visits to make changes that will up the price in the long run.

22. Choose a team used to extending cheaply

When you have early meetings with architects, surveyors, structural engineers and even builders, ask about their experience in working on low-cost projects and make your budget clear from the start. If they are happy to proceed on that basis, ask if they can produce planning and building regulations drawings for a fixed price.

Find the team you need at: Royal Institute of British Architects, Chartered Institute of Architectural Technologists, Royal Institution of Chartered Surveyors and The Institution of Structural Engineers.

23. Consider an alternative to cut extension costs

Could you avoid the cost of extending and instead convert a garage or convert a loft space into useful living space? Both are likely to be cheaper than building a new extension from scratch. 

More on extending your home: