Dormer's have been referred to in many different ways, Dormer windows, Dormer extensions, roof extensions, attic extensions - a brief description of a Dormer would be an extension of an existing roof shape. Consider a most typical terraced property/town house where the roof would start at the gutters at the front of the house rising to the Apex, (the ridge) in the centre of the house, then falling again down to the gutters at the back of the house. This most typical roof shape does not usually produce a substantial habitable room, unless the house is unusually large. So with this type of roof structure, it would be advisable to extend the roof and create a Dormer (usually to the rear of the property.)

The size, shape and general design of this or any other Dormer can vary greatly. This type of loft conversion may also not require planning permission. Householders have what is known as a permitted development allowance, usually measured in cubic metres. The amount allowed (cubic metres) varies from property to property. Generally, the allowance is between 50 and 70 cubic metres or 20% of the overall volume of the property we can easily calculate the required volume for any dormer and whether or not this would fall within permitted development rights.

Please note, there are further guidelines whilst trying to identify if your project would be allowed under permitted development rights. These are; (i) no part of the new structure must rise any higher than the existing highest part of the roof at present (usually the ridge line), (ii) looking down on a plan, no part of this new structure must exceed the current floor plan boundary and (iii) the property must not be in a conservation area. Again, as per roof line conversions, even if planning permission is not required, Architect's plans along with Structural Engineers calculations will be necessary to conform and to comply with the current building regulations.