B5.1.2 Dormer sizes

Dormers must remain subordinate and proportionate to the original roof in both scale and form by ensuring that they:

• do not project above the highest part of the existing roof

• avoid the appearance of a full additional storey, which can be achieved by:

  • maintaining a clear break from the main eaves line (minimum 0.2 metres)

  • setting the dormer in from the sides of the roof

  • setting the dormer down from the ridge of the roof

• do not overhang the outer face of the wall

Where dormers are constructed under Permitted Development rights, applicants are still encouraged to ensure that scale, materials and placement still respect the character and proportions of the existing roof and wider street scene.

For dormers proposed to the front or side elevations of a property that face the street, their width should be kept to a minimum to reduce visual impact on the streetscape. These dormers should occupy no more than one-third (33%) of the original roof slope.