The Complete Guide to Extending Your Home

Renovating your home can reap huge rewards. When done correctly, it helps you bring your home up to date and add value to it. Whether you plan to renovate a bathroom or extend your home within permitted development rights, you should approach your project with laser eye focus to stay on budget and complete it on time.

Why is it important to prepare for your home extension project

This helpful guide will allow you to plan your house extension expertly and to avoid the common mistakes that can eat into your budget before you even start. It will answer common questions that become obvious only once you start making mistakes! I learned the hard way during our recent single storey extension. So read on, to give yourself the best chance at a smooth house renovation.


  1. Find out if you need planning permission

  2. How Close to a Boundary Wall Can I Build an Extension?

  3. Do I need an Architect involved?

  4. What to Consider Before Drawing up Plans

  5. Who submits the planning application to Council?

  6. How long does it take for a planning permission to be issued?

  7. Do I need Building Regulations plans?

  8. How do I choose the right builder?

  9. What are the stages from planning to completion of a build?

  10. Who will keep track of payments?

  11. Can I make changes in the design during my build?

  12. Do I Need a Lawful Development Certificate?


1. Find out if you need planning permission

About 3 years after I achieved planning permission for our rear single storey extension, and another 2 months after receiving a Non material Amendment to my initial permission, I found out that I didn't need planning permission to begin with. This is because the size of my extension was within permitted development rights.

Under new permitted development rules, homeowners in terraced and semi-detached homes are able to put single story extensions of up to 6 metres at the rear of their properties without needing to obtain planning permission. Those in detached homes are able to extend by up to 8 metres.

To qualify for permitted development, the following need to apply:

  • your home has not previously been extended

  • your home is not listed

  • your home is not in a conservation area and there is nothing prohibitive in your deeds.

Tip: Do not assume that your home has been extended previously, even if you see a past planning approval. Check the original plans of the home versus what was approved to confirm whether any works had ever been executed. If you need confirmation, your local building control office will be able to confirm this.

2. How Close to a Boundary Wall Can I Build an Extension?

You can build right up to a boundary wall but know that if building your extension involves digging or building 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.

3. Do I need an Architect involved?

Assuming you have identified that you need planning approval, you will need to discuss your project with an architect who will provide the relevant plans and elevations to support your planning permission.

Do not expect the architect's drawings to include the detail of where things start and end. Everything seems to be drawn on approximation which can lead to frustration and will not help your builder down the line.

Here is an early iteration from my architect. The drawing looks cool. It incorporates a rooflight as well. But while drawn beautifully, this design is technically impossible to build. Why?

Because our architect already knew that our internal ceilings throughout our home have the very standard 240cm height. That would live just 10cm allowance for a roof. Well I can tell you, you cannot build a flat roof that is 10cm thin.

Tip: Instead of taking the measurements at face value, ask your architect for proof of concept. Ask them to split the height into the various sections. Ask them to further split the height they allocated for a roof to its various elements too.

If your architects numbers are not correct, you will lose more time trying to correct them once your plans have been approved and the build has started, and that is an absolute nightmarish situation. It may take a minimum of a month for the planning officer to review and approve non material amendments.

4. What to Consider Before Drawing up Plans

Although your architect should be able to advise on this, by visiting your property, some aspects can restrict what you can and cannot do in your design including:

  • soil type on the site (might require different type of foundations like beam and block)

  • services access (you cannot build over manholes)

  • surrounding trees (your foundations might need to be deeper)

  • any history of flooding

  • site access

  • rights of way.

5. Who submits the planning application to Council?

If you have an architect assigned, ask if they will submit the planning application on your behalf, acting as your agent. Having said that, if you have the drawings it is easy to submit the application yourself, there are no technical questions.

If you plan to save some money and submit for planning permission yourself, try to look up planning permission applications submitted recently by others in your area - these will be available on your local Planning Authority's portal, just look up by address to find recent applications.

The cost of applying yourself is less than £50. Your architect may charge around £400 to submit your application.

6. How long does it take for a planning permission to be issued?

If you require planning permission before you start your works, you will need to submit plans, showing the current and future design of your home. To do this, your architect will need to survey your home to get accurate measurements. Plans submitted must be to scale!

You should allow up to two weeks for the survey to take place (depending how busy the architect's surveyor is).

Once the survey is done, the measurements will be shared with the architect who will work on a couple of concepts to discuss with you. This stage can take as long as you need to decide on the final look and feel of your extension.

Once submitted to your local planning Authority, expect anything up to 12 weeks for your approval to come back. The local council will need to allow enough time for neighbours or the local Parish to raise any concerns before they make a decision on your case. This timeframe is relevant only where the council approves your plans without conditions.

7. Do I need Building Regulations plans?

Once you have your planning permission you can move to the next stage: Building Regulations plans: these are your builder's guide to building your home to exact specifications according to your architect and structural engineer.

These plans will show you where to fireproof walls, what insulation materials to use, ventilation requirements, drainage etc. They can also show in more detail specific parts of the build in line with the structural engineer's requests.

Your Builder will need to see these plans before providing their detailed quote. Knowing what I know now, I would suggest that you go through them with your Builder, in detail, point out the most complex parts and have them agree that they can carry out the job.

8. How do I choose the right builder?