The 45 Degree Code


People expect good natural daylight in their homes. In designing a new development or an extension to a building, care needs to be taken to safeguard the daylight to adjacent residential properties and protect them from overshadowing. The quality of daylight received by properties adjoining development sites can be severely restricted by buildings or extensions which are too close to the boundary or project too far into the rear gardens.

The Wyre Forest District Local Plan contains policies which aim to safeguard the amenities of properties adjacent to developments, including daylight. Planning permission will not be granted for development which unacceptably restricts daylight to neighbouring properties. In order to assess the impact of development on neighbours’ daylight the council will apply the 45° code.

How It Works

From the midpoint of the cill of the nearest principal habitable room* window (or in the case of patio doors, halfway down the door) measure two 45° angles from the window plane, thereby forming two lines diverging at 90° . The plane connecting the two lines is then tilted to an angle of 25° above the horizontal.

45Deg Code Eg1

There should be no obstruction above this rising plane.

The 45° line applies equally to ground and first floor windows as well as to side windows where they provide the only source of light to a habitable room.

* habitable rooms include kitchens but not for example bathrooms, w.c.’s, en-suites, landings, utility rooms or garages.



45Deg Code Eg2

The single storey extension shown is acceptable if limited in depth. (figure 3) But not if it is further extended. (figure 4)


45Deg Code Eg3  45Deg Code Eg4

Although the single storey extension breaches the 45° line in plan form, it is clear of the 25° tilt and therefore acceptable. It would not be acceptable though if it were a two storey extension.


The 45° code applies equally to conservatories or other extensions comprising of see through materials. Where the neighbouring property has a conservatory or similar immediately adjacent to the boundary, the 45° line is drawn at the centre of the original opening. Similarly where bay or bow windows are affected the line is drawn from the mid point at cill level at the back of the window where it joins the main wall.

The 45° code needs to be applied carefully and flexibly. We will take account of the particular circumstances at each site which might include orientation, differences in levels, existing structures, brick boundary walls (although not fences or vegetation which are less permanent than walls) and the distance between the affected window and the extension.

t will normally be unacceptable to design an extension with chamfered corners, asymmetrical roof etc. simply to avoid the 45° line as this leads to poor design. Please note that applications must satisfy other design principles as well as just the 45° code.