10 Ways to Cut the Cost of Your Extension

1. Keep your extension design simple

Curves and corners are costly to build, so keep your extension design as simple as possible. A rectangular or square footprint with a simple pitched roof is cheapest. Design the build around off-the-shelf products, such as standard-size doors and windows.

Avoid products that have to be made to order; choose materials that are readily available and easy to use. Avoid complicated ground works, such as building near to trees, drains, sewers or other buried services, as these will increase costs.

2. Save money with a DIY extension

Labour costs represent between half and two-thirds of the outlay for a typical extension, so doing some of the work yourself is a great way to save money.

The easiest tasks to take on are labouring, decorating and landscaping, followed by ‘second fix’ trades, such as kitchen and bathroom fitting, tiling and fixing architraves, coving and skirting boards.

Be careful only to take on work you have the time and skills to complete effectively. Unless you are an expert, hire professionals for the skilled work where the results will be on view all the time — for example, bricklaying and plastering.

3. Project-manage the extension

A builder will add 15–25% onto 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 trades people, directing the work and supplying all of the necessary materials, plus scaffolding, skips etc. Though time-consuming, it can be very rewarding and the savings can be enormous.

4. Save on VAT

Most extension work will attract VAT at 20% on labour and materials, but if you use self-employed trades people who each turnover less than the threshold for VAT registration, you will not be charged this tax. Second hand materials sold by private individuals online are also VAT free. Some types of work attract reduced-rate VAT — upgrading insulation and extending a building that’s been empty for two years, for example.

5. Keep in With Your Neighbours

If you are building on or near the boundary of a neighbour, your extension will need to comply with the Party Wall Act (England & Wales) 1996. If a party wall settlement is required, it will cost around £700 per neighbour; more if they use their own independent surveyors. 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, you can avoid using a surveyor to arrange a party wall settlement and save on fees.

6. Save on Fees

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.

7. Avoid cowboys

There are plenty of cowboy builders and they may vastly underestimate costs — through incompetence or deliberately to secure a job. They may then ask for more money for changes or ‘extras’ or demand some/all the money upfront, leaving you with no comeback if they fail to complete the work satisfactorily. To avoid being ripped off, always ask for references. Never, ever pay for building work in advance; pay only for work that has been completed and that you are happy with.

8. Measure Twice, but Cut Only Once

Making changes or mistakes that waste labour and materials is a major factor in the final bill for many projects. Measuring everything onsite, 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.

9. Reuse, recycle and repair

Existing materials can be reused or sold rather than thrown in a skip. Buying salvaged materials – online or from salvage yards – can be a lot cheaper than buying new. Second-hand items offering good value include roof tiles, bricks, internal doors, timber floorboards, fireplaces and roll-top baths.

10. Negotiate trade discounts

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. Always 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.