The Benefits of Extending

Extending your home can really make a difference in the way you live and enjoy your space. Whether it’s adding an extra bedroom for a growing family or having a larger kitchen, there are many benefits:

  • More natural light
  • More space
  • Keeping your home and not moving to a different location
  • Permitted development
  • Adding value to your property.

Building an extension not only improves your living space but adds significant value. Within London, a small 15m2 extension could increase the value of a house by an added £60,000. The important factors that affect the value rate are size, location and quality.

Why not check out the added value of your house with an extension on the following link:

Calculator – Will an extension increase the value of my house? 

Getting Started

Firstly, you need to secure planning permission; whether that be by seeking approval from your local council or benefitting from permitted development rights.

In simple terms, planning permission is seeking approval to do building works. Parliament has given your Council the power to assess particular proposed works against a national and local framework. Parliament has also passed Legislation which allows you to do some types of works without seeking planning permission from your local Council; permitted development.

So whether you need planning permission or not depends on what you’re proposing, and your local council.


Permitted Development

There are a number of types of home extensions/improvements you can do without planning permission, as long as they follow the guidelines. 

As an example, here are some of the conditions for erecting a single-storey rear extension:

  • extend beyond the rear wall of the original house by more than 4 metres in the case of a detached house, or 3 metres in the case of any other house. (under prior approval 8 metres in the case of a detached house, or 6 metres in the case of any other house)
  • exceed 4 metres in height.
  • the total area of ground covered by extension would exceed 50% of the total area of the curtilage of the original house.

As you can see, it can be quite complicated however with a planning expert it’s a breeze. It’s important to employ a competent planner, rather than an architect, as they have expertise and knowledge to understand and apply to the council. 

Non-compliance to the conditions could lead to intervention from planning enforcement which may result in having to apply for planning permission to the Council, or in the worst-case scenario carrying out further works to comply. To avoid all this, stick to a planning expert.

Can I benefit from Permitted Development rights?

This all depends on your property and your local council. If you own a house, not a flat or maisonette, then you could benefit from this right. You would need to check with your local council to see whether these rights apply within your area as some councils remove this right so that you formally apply for planning permission. A planning expert can help navigate through this and confirm whether your proposal fits within the rights.

Do I need to apply for Permitted Development?

Technically, no. The permitted development right for extensions is planning permission subject to conditions and limitations. You could crack with your extension as soon as you have confirmation from your planning expert.

However, it is recommended to apply for a Certificate of Lawfulness prior to the commencement of building the extension. The Certificate is a formal document from the local council confirming that the extension complies with permitted development and therefore it is lawful. It is a legal document and can provide to be essential when selling the property as the buyer’s solicitors may request this as proof. In addition, it is worth getting this approval as permitted development rights are amended by Parliament as and when deemed necessary.

Compliance & Regulations

Applying for a Certificate of Lawfulness

If you do apply for a Certificate of Lawfulness, then you would need to provide the following:

  • The application form
  • Architectural drawing plans (Elevations, Floor and Location Plans)
  • A fee 

The application form can be found on the local council’s website or you can apply via Planning Portal. A planning expert can manage the whole process with you liaising with an architect. Once the application is validated by the council, it could take around 8 weeks for a determination. 

Unlike a normal planning application, the council cannot refuse the Certificate if it complies with the permitted development requirements.

It’s important to employ a competent planner, rather than an architect, as they have expertise and knowledge to understand and apply to the council. 

Applying for Planning Permission

If you wish to build an extension that goes beyond the permitted development rights, then you would need to apply for planning permission to the local council. 

Submitting an application needs to meet validation requirements set by national and local standards. The essential document would be similar to a Certificate of Lawfulness, however, you may need to submit further documents:


  • Application Form
  • Architectural Drawing Plans (Elevations, Floor and Location Plans)
  • A Fee 


  • Design And Access Statement
  • Tree Report
  • Ecology Report
  • Flood Risk Assessment

Each council has its own specific list and therefore you may need to submit other documents to comply with validation requirements. 

Once the application has been validated, it is allocated to a planning officer to assess the proposal. The application is assessed against national and local planning policies taking into a number of considerations such as:

  • Design and Appearance
  • Character
  • Neighbour Impact
  • Local Constraints

It is therefore paramount that the application is considerate, aiming to enhance and complement the house and local area. 

A decision of the application would be issued usually by a minimum of 8 weeks. During the assessment the planning officer may discuss the application with you, however, they are not obliged to do so. Sometimes if it’s a tweak that would be more preferable for the council then it can be addressed by the architect. 

What happens if my application gets refused?

If your application is refused, there are two options you could take to secure planning permission. 

  1. Re-apply 
  2. Appeal

Your planning agent will be able to decipher the decision by the council and advise whether it is worthwhile submitting a revised scheme or appealing. 

Sometimes a refusal can simply be fixed by making an amendment and submitting a revised application. It doesn’t cost to re-submit, as long as it’s done within 12 months of the refusal. The only cost you may need to consider is for the architect to make these amendments and for the planning agent to re-submit, which shouldn’t cost much.

If an appeal is required, then this can be a lengthy process but sometimes prove to be worth it. It is advisable to use a planning expert to manage the process as it can be complicated and lengthy. You would need to submit an appeal to the Planning Inspectorate, an independent body to the local council, with an accompanying appeal statement and any required documents. 

Once planning permission has been granted, you then will need to proceed to get detailed drawings for compliance with building regulations, and for builders to use.

Building Control

As part of the building process, you need to comply with Building Regulations. 

Buildings are controlled by The Building Regulations which ensures that they are going to be built safe, healthy and high-performing. The regulations cover specific topics: structural integrity, fire protection, accessibility, energy performance, acoustic performance, protection against falls, electrical and gas safety. They also lay standards for drains, ventilation, protection against the ingress of water and protection against contamination including methane and radon gas. 

You would need to submit an application to the Council with drawing plans demonstrating compliance. A structural engineer will need to complete a survey and share their expertise with the architect to ensure the plans are correct.

The expected cost for the whole process would be similar to applying for planning permission.

The Build

The cost of a home extension will depend entirely on the:

  • Size of Extension
  • Location 
  • Structural Layout
  • Glazing

An important factor to consider could be where the extension affects a neighbouring party wall. A Party Wall Agreement would need to be drafted up where you may need to employ a party wall surveyor, which factors both yours and the parties costs.

You should ensure all the following items are clarified before agreeing with a builder to carry out your extension works:

  1. Detailed Quotation
  2. Building Schedule (Itemised and Costs)
  3. Project Management (Management of Build, Timescale, Quality Assurance)
  4. Considerate Builders Plan (Minimise disruption to yourself and neighbours, Routine Site Clearance, Protect House)
  5. Full Liability Insurance
  6. Payment Terms 
  7. Skip Hire
  8. Other Costs 


Here is a step by step breakdown of getting your extension completed:

Phase 1

  • Discussion with Planning Officer
  • Survey by Architectural Designer
  • Drawing plans
  • Obtain specialist reports
  • Submission of application

Phase 2

  • Meeting with Builder
  • Schedule of works and costs
  • Draw and prep plans for application 
  • Stages of inspection Agreement
  • Commencement of building works
  • Survey from Building Inspector
  • Completion Certificate

We hope this guide has given you insight into the process, the expected costs and some key details of compliance and regulations. For more expert advice or support with your planning application please get in touch.