Building regulations for extensions: full plans or building notice?

Planning permission is about what an extension looks like and its effect on neighbours and the area. Building regulations are about how it’s built, so that it’s safe, healthy and energy efficient. Almost every extension needs building regulations approval, even when it doesn’t need planning permission.

What building regulations cover

The regulations are supported by a set of Approved Documents, each covering a different subject. For a typical extension, the most relevant are:

• Structure: foundations, walls, beams and roofs.
• Fire safety, including escape routes from upper floors.
• Resistance to damp and weather.
• Energy efficiency: insulation, glazing and heating.
• Ventilation.
• Drainage.
• Electrical safety.
• Stairs, guarding and safety glazing.

Who checks the work

Building regulations are enforced by Building Control. You can use Cornwall Council’s Building Control service, or a registered building control approver from the private sector. Either way, they check the design and inspect the work on site at key stages, such as foundations, drainage and completion.

Full plans application

Detailed drawings and specifications are submitted and checked before work starts. The council must decide within five weeks, or up to two months if you agree to an extension, and the approval may come with conditions.

The advantage is certainty. Your builder works from approved drawings, prices are based on a known design, and problems are caught on paper rather than on site. For most extensions, this is the route we recommend.

Building notice

With a building notice, you give Building Control at least two days’ notice before starting, but no drawings are checked in advance. The inspector checks the work as it goes.

It can be quicker to get started, but the risk sits with you: if something doesn’t comply, it has to be put right, which can mean taking work apart. It also gives builders nothing detailed to price from. Building notices can’t be used in some situations, and they suit small, simple jobs better than extensions.

Regularisation

If work has been carried out without building regulations approval, a regularisation application can be made to have it assessed after the event. Parts of the work may need to be opened up for inspection. It’s a fix, not a plan, and it’s usually more expensive and stressful than getting approval first.

The completion certificate

When the work is finished and the final inspection is passed, Building Control issues a completion certificate. Keep it safe: buyers’ solicitors will ask for it when you sell, and missing certificates can delay or derail a sale.

Dutyholders and the principal designer

Since October 2023, building regulations also set out duties for the people involved in a project, including a principal designer and principal contractor where more than one contractor is involved. Our guide to the principal designer role explains what this means for homeowners.

How we can help

We produce full building regulations packages for extensions, coordinate the structural design with an engineer, submit the application and deal with Building Control’s questions, so your builder has an approved set of drawings to work from.

This guide gives general information for homes in England and isn’t a substitute for advice on your own property. Rules change, so check the current position before relying on it.