What you need to know about extensions and the building regulations

What you need to know about extensions and the building regulations

The building regulations will usually apply when you add an extension to your home. Although some extensions don’t require planning permission due to permitted development rules, you are still legally required to put appropriate building control in place for your project.

In this article, we will briefly outline the things you need to be aware of before work starts. However, we always recommend checking with your local council if you’re unsure about whether your project requires planning permission.

Typically, your building control inspector will be interested in the following elements of your extension:


Your building control inspector will carry out the first inspections at this stage of the build, checking the adequacy of the ground condition before concrete is poured. Key factors at this stage can include the presence of nearby trees, any adjacent buildings or drainage systems in close proximity.

Ground Floors

Ground floors are expected to have structural stability, resistance to damp and prevention of heat loss as well as sub-floor ventilation and dampproof membrane.

External Walls

To comply with the building regulations, external walls are expected to be weather resistant and minimise heat loss. They must also provide appropriate support for the structure.

Structural Openings

Your building control inspector will want to inspect structural openings as new extensions frequently involve creating openings in the main house’s existing walls. They will need to check any new openings are structurally sound. The alterations will usually be designed by a structural engineer and your building inspector will check that the work on site is in accordance with the design.

Upper Floors

If you are constructing a multistorey extension, inspection of the upper floors is also important as they will need to support loadings from occupants, furniture and internal walls.


Your chosen inspector will need to establish that an appropriate roof structure as specified within the plans has been put in place.


If your extension requires any alternations to drainage systems, this work must comply with Part H of the building regulations.

This is not an exhaustive list of everything your building control inspector will look at, different projects will have different requirements but your chosen building control body will explain to you when they will need to inspect your work.

It is also worth considering whether the Party Wall Act will affect your extension. If you have a neighbouring property nearby, you may need to notify them as dictated by the Act.

Thank you for taking the time to read our guide on extensions and building control. The information in this article is not official advice and we would always recommend speaking to your chosen building control body or other appropriate parties before carrying out work at your home.