The 45 degree code is one of the factors your local council will take into account when determining your planning application. The 45 degree code is used on both new builds and extensions which may affect the outlook from, or the daylight to a nearby house or flat. A line is drawn at an angle of 45 degrees from the nearest front or rear window that would be affected, this window must be the main source of light from a habitable room.

Single Storey Extensions

Any design which requires planning should not cross the 45-degree line, if the extension is single storey the measurement is taken from the mid-point of the nearest ground floor window.

Double Storey Extensions

If the extension is at the first floor the measurement is taken from the quarter point of the nearest first floor window. If the extension is double storey the ground floor window is also measured from the midpoint.

Building an extension in two stages

If you are planning to build a double storey extension in two stages, it is important to remember that the code will be applied when the further storey is added to an existing single storey extension.

Neighbours building a joint extension

Neighbours can submit a joint application for extensions built at the same time. In this case the extensions may be allowed to be calculated on the new 45-degree lines created by the neighbour’s extension. In these cases, neighbours must confirm at the time of the application submission that this is what they would like to do, however the planning office makes the final decision on these cases.

Bow or Bay Windows

If the neighbouring property has a bow or bay window the measurement will be taken from the mid or quarter point at the back of the window where it joins the main wall of the house or flat. If the bay has solid brick sides which extend the full height of the window opening, the measurement will be taken from the glazed part of the window itself.

Terraced houses

In the cases of terraced properties, those that are built with a ‘wing’ section which already breaks the 45-degree code it is not normally acceptable to build an extension which fills in the gap to the side of the wing. As it will nearly always break the code. Single storey extensions at the rear of the wing will be looked upon their merits as long as they leave enough garden space. Two storey extensions to the end of the wings are not normally allowed.

Although this document covers most of the circumstances that may affect the code please refer to your local council's website should you require further clarification.


What if the neighbouring property has an existing extension?

If the neighbouring property has an extension the line will be taken from the nearest habitable room window of that extension, on the basis it is going to be the window most likely affected.

What if the neighbours have a conservatory?

If the neighbours have an extension mainly made from glass the code will then be applied to the original window opening in the wall of the house where the conservatory has been added.


We use cookies and similar technologies on our website to help provide you with the best possible online experience. By using this website, you agree that we may store and access cookies and similar technologies on your device. Find out more.