What are Building Regs for an extension?

Building regulations are requirements to ensure that your extension has been built safely and to the required standards. These rules apply to all types of building and construction and are enforced to look after the safety of homeowners living in properties with an extension.

As a homeowner, you are responsible for obtaining any building regulation approvals. Some contractors will manage the inspection process for you. Others can self-certify their work as compliant and are known as members of the Competent Person Scheme.

What types of extension require building regulation approval?

Building regulations cover most areas of construction:

  • Electrics: making sure new electrical outlets, wiring and fittings are safe.
  • Heating: checking new boilers or heating appliances are fitted correctly.
  • Fire safety: ensuring construction work is up to fire safety standards and there are sufficient escape routes.
  • Structure: verifying that walls and joists are robust and can safely bear the load. This includes garages, balconies, conversions and new floors.
  • Plumbing: make sure new plumbing fittings have been installed correctly.
  • Ventilation: certifying that ventilation is sufficient and that doors and windows are safely installed.

Other types of build that may require inspection include waste disposal systems and drainage works.

What extension works do not require building regs approval?

Some minor alterations do not require certification. These include:

  • Replacing a bathroom.
  • Unheated conservatories provided the original external doors remain in situ.
  • Greenhouses.
  • Work to existing electrical circuits.
  • Carports (with some exceptions).


How do I apply for Building Regs approval for my extension?

You can apply for approval through your local authority, a private approved building control inspector or your contractor if they are part of the Competent Person Scheme.

The process depends on your extension and will require you to either submit full plans or a building notice.

Full plans building regulations – this process involves sending complete plans and design specifications to your local authority. They will be reviewed within 5-8 weeks, and the approval remains valid for three years once granted. The local authority inspector will visit the site at stages to ensure that the build is compliant.

Building notice submission – whilst some complex extensions might not be permitted via this route, building notice means advising the local authority of your intent to build without the expense and time needed to produce full plans. As with a full plan submission, the inspector will visit the site during the build. A Completion Certificate is issued once the extension is completed to their satisfaction.

How much does Building Regs approval cost for an extension?

The cost depends on the size and scope of your extension, and inspection fees usually relate to the cost of the work. These are usually around 1-2% of the cost of the extension, so for a £20,000 project, you might expect to pay Building Regs fees of around £200-£400.

Most local authorities charge around £100 submission fee for full plans, and additional fees for inspections. The number of inspection visits and regularity will depend on how long your build is expected to take, and when the most important works will be carried out.

Frequently Asked Questions

Can I get retrospective Building Regs approval for my extension?

Yes, you can apply retrospectively for approval through a process called regularisation. Be aware that if your extension is not compliant with any of the building regulations then you will need to have repairs or corrections carried out to obtain certification.

This application does carry a charge, although how much this costs depends on your local authority. Typically, the cost will be calculated against the value of the original work.

What happens if I build my inspection without Building Regulations approval?

If you have applied for Building Regs approval but had your application rejected, you can amend your extension plans to be compliant before the work is carried out. If you do not wish to, then you also have the right to appeal.

Should an extension be built without authorisation and without complying with building regs, this can be serious. You might be instructed to remove or correct any part of the build that is not compliant, and if this is not completed within the timescale allocated then the local authority may issue a 28-day order, along with a charge for the costs incurred.

Alternatively, they may seek prosecution and a conviction can cost a fine of up to £5,000 with additional fines of £50 per day that the extension remains non-compliant.

In extreme circumstances, a local authority can elect to carry out corrective works themselves, with the costs payable by the owner of the property.

What parts of my extension will be inspected?

Building Regs cover inspections of most parts of an extension, including:

  • Roofing
  • External and internal walls
  • Windows
  • Doors & doorframes
  • Kitchens
  • Bathrooms
  • Electrics
  • Drainage

Do I need a certificate to confirm that my extension meets Building Regs?

Once your building work is complete, you will need the completion certificate from the local authority to verify that all the requirements have been met. This is important to have since it formally authenticates that your extension is compliant with regulatory standards.

If, for example, you had cause to make an insurance claim and could not verify that your extension was built up to standard, it could cause problems.

Completion certificates should be issued before the final payment is made for the work to ensure that any corrections are made. If your contractor is a member of the Competent Person Scheme they will issue the certificate within 8 weeks of finishing work.

Make sure to obtain your certificate before you part ways; these cannot be issued retrospectively.

Mike Alexander
Hey there, I'm Mike - writer and part time home improvement expert at Refurbb. Since owning and refurbishing my own property in 2018, I've since been developing rental properties, writing about my home improvement endeavours, sharing what I've learned and connecting readers to reputable tradespeople in the UK.

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