B5.1.5 Impact on neighbours and the streetscape

Guidance: G5.12

To protect light and outlook for neighbouring properties, extensions should demonstrate (through drawings and sections) that proposals comply with the 45-degree and 25-degree rules:

• 45 degree rule: A 45-degree line is drawn horizontally from the centre of the nearest habitable room window (e.g. living room, bedroom, or kitchen/diner) on the neighbouring property. The proposed extension should not cross this line, as doing so may cause unacceptable overshadowing or obstruction.

• 25 degree rule: A line is drawn at a 25-degree angle at the level of the centre of the lowest window from the neighbouring property. The proposed extension should not extend beyond this line to avoid causing excessive overshadowing or loss of natural light.

Exception: This design guidance is strongly encouraged but does not apply to dormers constructed under Permitted Development rights where planning permission is not required.

Sketch showing a house elevation with a proposed extension highlighted in orange. Corresponding plans show an acceptable and an unacceptable extension depth when considering the 45-degree rule.

Figure 146: Shows plans which demonstrate the 45-degree rule - the left plan shows an extension that stays within the 45-degree line, while the right plan extends beyond it and is therefore unacceptable (Guidance: G5.12)

Sketch section showing two houses. A 25-degree line is drawn from the centre of the lowest window from the house on the left of the sketch. To the right, an acceptable example of new development is shown, as well as an unacceptable example which crosses the 25-degree line.

Figure 147: Shows a sketch illustrating the 25-degree rule for protecting light and outlook (Guidance: G5.12)

Guidance: G5.13

Extensions on prominent corner plots should maintain active frontages on both streetfacing elevations, avoiding blank walls or inactive façades. Where the rear of the corner plots extension is visible from the public realm the extension should also be set back by a minimum of 0.5 metres from the street. For all other extensions visible from the public realm but not located on corners, designs should respect the established street rhythm and ensure visual interest is maintained, avoiding overly blank or featureless elevations where they face the street.

Guidance: G5.14

Dormers proposed to the rear and side of a property should minimise overlooking to neighbouring properties by:

  • adhering to the separation distances set out in Code: C5.11, based on the applicable Area Type

  • where separation distances cannot be achieved on side elevations, using design solutions such as obscure glazing or high-level windows to protect privacy

Exception: This design guidance is strongly encouraged but does not apply to dormers constructed under Permitted Development rights where planning permission is not required.

3-D model line drawing of a two-storey suburban house with a 1.5 storey side extension. Side extension has a gabled dormer window and is subordinate in size to the original house.

Figure 148: Shows a sketch view of a side extension on a corner plot, which maintains an active frontage to both street elevations by incorporating proportionate windows on the front and side of the extension (Guidance: G5.13)