ow to start planning a home extension

How to start planning a home extension

Extending your home is one of the biggest projects you’ll ever take on in your life, so to avoid coming to grief like some of the couples in Grand Designs you need to plan your extension thoroughly.

There’s much to consider on such a complex project, starting with your reasons for doing it.


What are your goals?

Because extending your home will need you to commit a significant amount of financial, time emotional resources, it’s worth starting by sitting down and asking yourself, and anyone else involved, what you’re hoping to achieve.

Maybe you need more space for your growing family, add a proper home office, want to bring an elderly relative to live with you, make your retirement home a bit more spacious or add value to your property with a view to selling it on before retiring.

Whatever your goal/s, you need to be clear and agreed on them from the start with whoever else needs to be involved.


Is a home extension the best way to achieve your goal/s?

Would moving house to a bigger one be a cheaper and quicker way to create space for your growing family? Or adding a heated outdoor shed in the garden be good enough for the home office you expect to be working from for some time yet?

If adding value is your goal, speak to a well-recommended local estate agent - as they can give a professional view on how much value your planned extension would add to your home. That would allow you to calculate the cost/benefit of the project, at least in the short-term.

If you decide building an extension is the best solution, read on.


‘Permitted development’

In most cases, you don't need to apply for planning permission if the extension meets certain rules. This is called 'permitted development'.

These rules depend on how many storeys your extension will have.


If your extension will only be on one storey, generally you don't need planning permission as long as:


  • It's at the back of the house
  • It doesn't go back further than 3 metres if it's a terraced house, or 4 metres if it isn't
  • The height of the eaves (where the wall meets the roof) is no higher than 3 metres
  • It's not higher than 4 metres, including sloping roofs
  • It doesn't cover more ground area than your house does
  • It doesn't take up half the 'curtilage' - the grounds behind your home
  • It isn't within a conservation area


If your extension will have more than one storey, you don't need to apply for planning permission if:


  • It's at the back of the house
  • There's at least 10 metres between the extension and the boundaries of your grounds
  • It isn't higher than your home (excluding chimneys)
  • It doesn't cover more ground than your original home does
  • It doesn't take up half the 'curtilage' – the grounds behind your home
  • It isn't within a conservation area


Other approvals

It’s also a good idea to check with your council's planning department if you need to apply for planning permission as, even if you don't, there may be other approvals you'll need to get, such as ones relating to building regulations.

If you don't own the land your home is on, you may need to get the permission of the landowner.

If you live in a listed building you will probably also need to obtain listed building consent.

Don’t forget – it's your responsibility to make sure you get any necessary approval before work starts as you will be held liable for any work done without it and have to pay for any remedial work to remedy the situation! This is where a professional architectural design team or architect can be invaluable – being aware of the relevant rules and permissions required in different situations and areas.



Building projects are a major cause of disputes between neighbours. If planning permission is needed for your extension, your neighbours will have to be consulted by your local council, so it’s a good idea to let them know about what you’re thinking about from the start.

This way they can feel involved, are more likely to agree and your designer can take into account any feedback from them on limitations to the design they’d wish.


Find and brief a designer

While there’s no requirement saying you have to use an architect or architectural designer to plan and manage your extension, it’s clearly a lot easier and less stressful to have a professional draw up the designs and manage statutory permissions and your project from start to finish.

Finding the right one for you is a matter of asking people you know, looking at the websites of the relevant professional bodies and researching each firm’s past projects and their client testimonials.

When you first meet your chosen designer, it’s crucial you give them as much detail as possible on what you want from the project, any timings you have in mind, payment terms, and what penalties will be in place if deadlines are missed. They will then send you a detailed letter along with a contract to sign.


Get in touch

All Design is a dedicated, friendly team of architectural designers who work alongside external associates and consultants to help people across Scotland find property solutions through carefully considered designs which respond to their needs, the site, budget and planning policy.

We have more than 30 years of experience in the industry and thrive on using a creative yet practical approach to design to improve space for people.


To discuss your requirements or for more information please get in touch.

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