Adding an extension to your property is an effective way of creating more living space, perhaps to give current occupants more room, or to accommodate a growing family or an elderly relative. It is often a more economical option than moving house, not least because buying a new property incurs stamp duty and estate agent fees – which in some cases might amount to the cost of an extension itself.

Below is a step-by-step guide to the main challenges you will face as you advance from deciding to build an extension in the first instance, to moving into the final structure.

1. Consider these questions before you go ahead
  • Will you build one or two storeys? Compared to a single storey, a two-storey structure won't cost much more per square metre because you will need to pay for the most expensive elements anyway: the foundations and roofing.
  • Access: will building the extension limit off-street parking? If so, you may encounter problems as regards planning permission.
  • How will a builder bring materials to the plot? Will they be able to access the site easily, from the rear for example, or will all materials need to come through the property?
  • You should also consider soil condition, services, nearby trees (roots, overhanging branches), rights of way and any flood risks.

2. Ask advice from an extension veteran

Try to find someone who has been through the process before. No doubt you will have plenty of questions for them. Ask them if they can recommend a good architect and/or builder.

3. Work out the costs

How much your extension will cost depends on many factors, not least of which is the quality and complexity of the design. As a rough guide, a cost of £1,000–£2,000 per square metre should be expected. You may also wish to employ an architect/designer or structural engineer, which will be an additional cost. Although there is currently no law stating you have to, it could be very prudent to do so if you are not 100% confident in designing a safe structure.

Balance the budget for your extension with the value it will add to the overall property.

4. Consider how you will finance your extension

For a small extension, an interest-free credit card is a good option. For a larger extension, you might consider a personal loan – usually available up to the value of £25,000. If you need more cash than this, consider remortgaging your home or taking out a secured loan to get the required capital.

5. Work out the outgoings at each stage of the project

In general, builders will take payments at different stages of the building process. Costly items should be purchased in your name, in case the builder goes out of business.

An architect will require payment as they work. An accurate quotation is important in order to get a good idea of the final cost.

Establish who pays the local authority application fees – you or the architect?

6. Take advantage of reduced VAT for empty properties

If your property has been empty for two years, it will be treated as a conversion and will attract reduced VAT of 5%. Your builder will need to be VAT-registered for this to take effect.

7. Work out if you need planning permission

Not all extensions require planning permission. Permitted Development Rights mean that in certain circumstances you can begin building without telling your local authority. Learn about the criteria on the website.

Note: Extensions built on properties in National Parks or Conservation Areas will probably be subject to reduced Permitted Development Rights.

8. Visit your local planning office if unsure

Informally visit your local planning office and ask them if what you have in mind will require planning authorisation. Making any changes to a listed building will require planning permission.

9. Make sure you meet Building Regulations

Building Regulations are laid out by parliament and cover aspects of a dwelling such as fire safety, insulation, drainage and access.

You can either submit a Full Plan Submission or a Building Notice. The former requires more detailed advance planning, but could reduce the chances of you contravening any regulations. A Building Notice, by contrast, is the riskier (and potentially costlier) of the two, since you may only find out you have a compliance issue after work has been done.

10. Make sure you get on with your builder

You will be in contact for a long time so it is important to get on with your builder on a personal basis.

11. Get a warranty from your builder

If any structural defects or faulty workmanship become apparent, you will only have recourse if a warranty was provided before work commenced. This may also focus the builder’s mind on doing a good job.

12. Choose a suitably experienced designer

Find an architect/designer/engineer with experience in the type of extension you're planning. If your property is in a Designated Area, try to find a designer with appropriate experience in this too.

13. Consider architectural technologists as well as architects

Architectural technologists are those who studied architecture but have not completed all the applicable exams. For smaller extensions, these professionals might be suitable - and may cost less than a fully-fledged architect.

14. Choose an architect registered to a reputable institution

Like builders, home designers do not need to be registered with any particular organisation or agency. However, choosing one that is affiliated with a reputable architectural body is a prudent step.

Among the main bodies are the Royal Institution of Chartered Surveyors (RICS) and the Chartered Institute of Architectural Technologists (CIAT).

Make sure your designer carries sufficient professional indemnity insurance (PII). And be aware that if you carry out the designing yourself, you will need your own PII.

15. Find a reliable builder

No easy task, but you should make the effort to find a reputable, reliable builder who you get on with. Personal recommendations can assuage any worries over skills, experience or character.

16. Get a detailed quotation from your builder

A builder should be able to give you a detailed quotation if you have provided sufficient information. Avoid day work rates as they can push costs up. If VAT is to be added to the bill, make sure the VAT registration number is detailed on the receipt. Less reputable builders may charge VAT but keep the additional money for themselves.

17. Find multi-skilled tradesmen

In the interests of continuity and cost savings, it will be of huge benefit if you can find a group of tradesmen who each boast a range of skills. For example, having access to two people who are skilled electricians could eliminate any down-time caused by non-availability of a particular electrician. When hiring tradesmen, remember that ‘the buck stops with you’. You will be responsible for things like keeping the site tidy and taking out applicable insurance.

18. Decide whether to move out during construction

Given the disruption and noise associated with extension building work, you may decide to move out for the duration. Some decide to move into a caravan in the garden – although this may not be practical for large families. Renting rooms nearby is a costlier alternative.

Moving overseas for the duration of the work and leaving your builder unsupervised is not recommended.

19. Planning for additional heating and electrical circuits

Work out if your existing boiler is able to cope with the additional demand of the extension. Equally, decide if you need an additional electrical circuit – although this is usually only necessary if you are adding a kitchen. always recommend seeking the services of a professional tradesperson If you're not entirely comfortable carrying out repairs or maintenance by yourself.