Class B - Roof Additions Under Permitted Development
Class B of permitted development covers additions or alterations to roofs which enlarge the house, such as loft conversions involving dormer windows.
This means many loft conversions can be carried out without the need for a planning application, provided they meet certain criteria.
Types of Loft Conversions
Dormer Loft Conversion
The most common type, involving an extension projecting from the slope of the roof to create additional floor space and headroom.
Hip to Gable
Extends the sloping side of a hip roof outward to create a vertical gable wall, maximising internal space.
Mansard Loft Conversion
Alters the roof structure to create a nearly vertical wall with a flat roof on top. Usually requires planning permission.
Velux/Rooflight Conversion
The simplest option, using roof windows without altering the roof structure. Often doesn't require planning permission.
Permitted Development Limits
To qualify as permitted development, your loft conversion must meet these requirements:
Volume Allowance
Maximum 40 cubic metres for terraced houses, 50 cubic metres for detached and semi-detached houses.
Materials
Materials used must be similar in appearance to the existing house.
No Balconies or Verandas
The extension cannot include a balcony, veranda, or raised platform.
Side-Facing Windows
Any side-facing windows must be obscure-glazed and non-opening (unless 1.7m above floor level).
Note: These permitted development rights do not apply to flats or maisonettes, and may be restricted in Conservation Areas, AONBs, or for Listed Buildings.