What is the 45 degree rule and why is it important?

If you are considering building an extension to your home or making other alterations to your property, you might have come across something called the 45 degree rule.

This is vitally important, particularly when it comes to planning permission.

When taking on new projects, particularly single storey extensions, we often get asked that the 45 degree rule is.

So, in this blog, we’re going to go over the 45 degree rule and outline how it can impact your ideas for home improvement.

What is the 45 degree rule?

Basically, the 45 degree rule relates to how a planned development, such as an extension or new build, will impact sunlight and daylight on neighbouring properties (known as the ‘right to light’).

There are two ways this can be measured, horizontally and vertically and it should be an essential part of any structural drawings and calculations.

It is important to note that the horizontal and vertical measurements are taken from a nearest ‘habitable room’ of the neighbouring property (for example,a  living room, bedrooms, a kitchen or even a conservatory). It doesn’t include other rooms such as utility rooms or bathrooms.

Horizontal

This is the primary way in which the 45 degree rule is applied.

Once you have your drawing for your proposed extension or development, a line is drawn from the nearest window of your neighbours property. A 45 degree angle is added, so if your planned extension falls outside this line, it shouldn’t impact your plans.

Vertical

The 45 degree rule also applies vertically.

This mainly applies to two storey extensions but the basis is still the same. An imaginary 45 degree line is drawn from the nearest habitable room of a neighbouring property to check if your proposed extension will impact daylight and sunlight.

Can the 45 degree rule impact planning permission?

Planning applications and applying for planning permission can be a pain, but it is an important step in ensuring your alterations are legal and compliant.

Your planning application will usually be rejected if it does fall foul of the 45 degree rule, so it is best to ensure that this is considered by an experienced architect first, to avoid any issues down the line.

What about permitted development?

Certain extensions and property alterations don’t require planning permission; however, the 45 degree rule still applies.

If you go ahead and build your project which then impacts on the daylight getting into a neighbouring property, you could face legal action. Even though you might be able to build under permitted development rights, that doesn't mean that the 45 degree rule shouldn’t be considered.

Getting the right advice

Planning, designing, and building an extension to your home can be a minefield.

This is why it is important to get expert advice and help, especially around things such as planning permission and ensuring any proposed plans are compliant with the 45 degree rule.

Get in touch with our team to find out how we can help your proposed development go as smoothly as possible.