The 45-degree Rule

The 45-degree rule is a common guideline used by local planning authorities to determine the impact from a housing development proposal on sunlight and daylight to the neighbouring properties.

If you’re thinking of a home extension or a change to your home, and need some advice, get in touch! We are here to advise you on how your home could be changed without affecting your direct neighbours.

When thinking about extending or making changes to your house, it’s crucial to think about the impact that it will have on your direct neighbours, as the planning authority will consider this.

Some quick facts about the sun, which will put the 45-degree rule into context:

• The Sun is at it’s maximum height around noon
• The Sun is lower during winter months, with shorter days
• In reverse, the sun is higher during summer and our days are longer
• The Sun rises in the East and sets in the West
• The Sun is due south around midday

When extensions are poorly designed or the factors stated above are not considered, it can greatly affect the main living spaces of neighbouring houses. Rooms such as utilities, hallways and bathrooms and even gardens are rarely considered as acceptable grounds for planning refusal.

There are 2 methods to he 45-degree rule, 1 considers the depth and the width of the extension and one considers the height

With method 1, you work out the depth and width of the proposed extension, draw it in plan form and mark your neighbours’ houses on the plan too. You then need to mark the nearest window of a key room in the neighbouring houses and mark a 45-degree angle on to the drawing to ensure that your plans to not fall inside of this. The centre point should be the centre of your neighbour’s window. If they do, a change will need to be considered.

With method 2, you will need to calculate the height and width of the proposed extension. Draw out the plan of the front or back of your house (depending on where the extension is), and include your neighbour(s)’s house on the drawing too. Mark the centre point of your 45-degree angle on the top of the window of the nearest key room of your neighbour’s property to see whether your plan will affect your neighbours.

Now, this is not something that we expect you to know about or consider before you come to us, we just thought this would be useful to read about if you were thinking of a home extension in future.

Have any questions? Get in touch!