What to consider before planning an extension

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There is a lot to consider when planning an extension or major works to your home. The need for extra living space and not wanting to leave your current home are two of the main reasons for building an extension.

From the design stage, to planning, through to working out costs and the actual build project – building an extension is a big commitment.

To help your project run smoothly we’ve put together this beginner’s guide to building an extension, which provides a run-down of what you need to know before you start.

Any shared walls

If building your extension involves building or digging foundations within 3m of the boundary, party wall or party wall structure, or digging foundations within 6m of a boundary, the work will require you to comply with the Party Wall Act.

Site access

How easy will it be for deliveries to be made to your home when building an extension? You’ll need to factor in how trucks and lorries will reach the property and unload large items and materials. You’ll also need to determine where traders will park and store their tools.

Demands on your services

Don’t forget to give your current services a health check. Don’t assume that your electrics, heating and plumbing will be able to cope with lighting and heating extra space. For example, while replacing the boiler is an option, you could also look at alternatives such as under-floor heating.


Importantly, notify your insurer of the work. Some may not provide cover during the works, but others offer dedicated extension insurance products.

If you are carrying out extension works and are managing the project yourself, you should arrange Extension Insurance to cover the new works and the existing structure. This is because most home insurers will exclude loss or damage whilst the property is undergoing alteration or renovation.

Do I need planning permission when building an extension?

Not necessarily. In many cases you will be able to build an extension under Permitted Development (PD) (these rights allow certain works to be carried out to your home providing you meet the criteria).

You should bear in mind that if your house is in a Conservation Area or a National Park, the amount of work allowed under Permitted Development is usually reduced.

If you’re planning a significant extension you’ll likely need planning permission and will need to submit an application. Engaging with your local authority early on and researching local planning policies to know what’s likely to get approved is a good idea.

Building regulations for building an extension

Whether you require planning consent or not, you will need to make sure you comply with Building Regulations. To meet the Regs, you can either submit a Full Plan Submission or a Building Notice.


Getting a warranty for your extension is advisable as it will cover you for things such as structural defects or faulty workmanship. Should the worst happen, the builders who did the work will need to return to put right what has gone wrong.

Finding an architect or designer

Choosing the right person to draw up your plans is as important as choosing the right builder, and the prospect can be just as daunting.

The key is to do your research, look at previous work and ideally speak to past clients, and choose someone who most closely aligns with your design aspirations, and who you feel you can work with best.

Who will manage the work?

You can use a design and build company who will manage the build project for you, but if you’ve used an architect or designed the extension yourself then you’ll need to find a main contractor to manage the project.

Finding a builder

If there is one thing that is more difficult than finding the right builder, it is getting on with him throughout the project.

Obviously a good recommendation helps, but it is wise to talk to previous clients of the builder. You should also ensure that they have Contractors All Risks Insurance.

To find out more about extensions and how the Homebuilding Show can help you achieve your dream home, visit a show near you. Find out more at homebuildingshow.co.uk