The cost of an extension can make or break a project, so we're here to tell you how you can save at all the different design, planning and building stages, to make room for a more successful result – without going over budget.
How much you can save will largely depend on the type of extension you want, but there are plenty of ways to tweak your design, or even just your approach to the project altogether – to keep your house extension costs low – without sacrificing what you want.
Check out our guide to extending a house for a complete breakdown of how to budget, plan and design your home improvement project, and keep scrolling for our roundup of ideas on how to curb your extension costs.
How can I extend cheaply?
Follow our advice below and remember that summertime is the best time to make a start on your extension, especially in the UK, as you've a better chance of dry weather. And, good weather will help work progress forward smoothly, reducing the need for any last minute alterations, and therefore, keeping your extension costs in check.
1. Do your sums then cut the cost of an extension
Save money by extending at the best time of year
Timing your extension for good weather is one of the simplest ways to cut the cost of an extension. 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. You can do this using our extension cost calculator, 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.
2. Consider building 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 reduce the cost of an extension 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 and specific extension costs for this type of project.
3. Keep interior fit outs simple too
Interior fit out costs can be kept down too. Obviously, you can choose to shop for affordable flooring, lighting and fixtures, such as kitchen units, but planning your project carefully and in great detail before work starts – right down to the position of electrical sockets and lighting controls – and avoiding making changes as you progress will keep costs under control. For more information on kitchen extension costs have a read of our guide.
Find out more on project managing an extension or house renovation yourself in our guide.
4. Plan ahead in detail to extend a house cheaply
Spending time planning the smallest of details can save you money and limit the cost of an extension 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.
If you are struggling with your space and wondering what kind of extension will work for you, or just what to do with your budget, check out the Real Homes Show. Every fortnight the Small Space Squad visit a homeowner trying to make their home work for them
5. Stick to the agreed design to reduce house extension costs
Then, it's important to stick to the agreed design if you want to cut the cost of an extension.
‘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.
6. 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 with all building extensions. 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.
7. Use affordable cladding to create a contemporary look for less
Yes, you can cut extension costs by being a bit clever with cladding. Because, cladding or rendering the exterior of an extension built with a timber frame or block work will work out much more affordable than facing it with brick.
Ideal for giving an extension a contemporary finish, it can suit both modern homes and period properties. Bear in mind that some cladding materials will need more upkeep and maintenance than others – read our guide to exterior claddings and renders to pick the right finish for your extension.
8. Build a timber frame extension to cut costs
Timber frame extensions can help cut extension costs as although the materials can work out a little more expensive than building with block work, the speed of the build can make up for that in lower labour costs.
Better still, timber-frame extensions can be finished to look no different to one constructed from block work, so aesthetics don’t have to be a consideration.
Expect to pay from around £1,800 per square metre. Find out more building a timber frame extension in our guide.
9. Cut the cost of an extension 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. Find out more about what to consider when extending a house in our ultimate guide.
Read more: Maximise natural light with a glass extension
10. Project manage yourself to reduce your building extension cost
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. So you can save on the cost of an extension 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.
11. 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.
12. 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.
13. 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.
14. Save on extension costs by building under permitted development rights
This will instantly save you spending on 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.
The above extension built under permitted development transformed the awkward ground floor layout of the home Louise and Dave Brown share with their two boys. ‘Our house had a weird L-shaped half open-plan design,’ says Louise. ‘You’d come in the front door and there was only one way to access the rest of the ground floor through the living and dining room. It was like a corridor. The house had a conservatory at the back – a lean-to design that was about 40 years old. In summer it was way too hot and in winter it was freezing.'
15. Comply with building regulations to reduce the cost of an extension
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.
16. 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.
17. Measure twice, but cut only once to reduce the cost of an extension
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 as already mentioned, and 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.
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18. 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 when building an extension as all they need is to be 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.
19. Buy secondhand to save on the cost of an extension
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.
20. 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. Remember to comply with Covid-19 Government safety standards at all times.
21. 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.
22. 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.
23. Maximise space with a mezzanine
Provided your ceilings are high enough, a mezzanine area could provide extra space for sleeping, with room beneath for a home office or just a quiet nook to relax in. Scandinavian Loft designs, creates and installs bespoke solutions to fit your space, with a standard or custom-size bed. The lofts come in a range of different materials and finishes including mdf, birch ply and metal and in your colour choice or with natural varnished oil. Customise your design with safety rails, bedside tables, ladders, stairs, storage, LED lighting and electrical sockets.
This birch ply mezzanine loft with stair storage costs from £6,000, from Scandinavian Loft.
24. Find a problem-solving builder to cut the cost of an 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.
25. Visit the site regularly to better control extension costs
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.
26. Choose a team with experience in 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.
27. Reduce your house extension cost by considering an alternative solution
Could you avoid the cost of extending and consider a garage conversion or loft conversion instead? Both are brilliant options to transform dead space into more useful living space, which is what many of us are looking for at a time when we're spending more time at home. Both are likely to be cheaper than building a new extension from scratch, food for thought.
You could even consider adding a garden building, which makes for a sound home office upgrade if you've been working from home for the past few weeks, and due to continue this way for the foreseeable future. You'll be (we can't promise) largely uninterrupted by the chatter of family life and it will help separate work life from time spent at home with others too.
Architect Richard John Andrews designed the above garden studio for his practice in East London and self-built it with his assistant for just £12,500, using a timber frame modular system with sheets of plywood. It’s clad in lightweight corrugated fibreglass panels, topped with a polycarbonate roof and has bespoke timber sliding doors.
28. Such as adding a bedroom over an attached garage
Assuming the garage's existing foundations can take the load, building a room on top is much more cost-effective alternative to building a new extension – plus you won't be sacrificing garden space to gain a new room.
Check with an engineer or surveyor about structural challenges, and hire a designer and a good builder to ensure that the new room feels like a natural part of the original house inside, and looks like it's original from outside, too.
Expect to pay from around £15,000 to £25,000 for this type of extension; building regulations and planning permission both apply.
29. Talk to an estate agent first
Before you even begin to think about extending, talk to a trusted local estate agent about the knock on effects of it on the value of your property overall. Most will be available over the phone and will have their Covid-19 company update on their website to help organise the best way of getting in touch. Forever home or investment for a quick buck – whatever your future intentions, you'll want to ensure that the spend you have planned does not exceed how much value you'll add to your home with the extension. Breaking even in a forever home isn't terrible; coming out in profit with an investment property is ideal; spending more than you increase the value of the house by is never a great idea.