A dormer conversion explained | Landmark Lofts

Dormer conversion explained

Commonly constructed at the rear of the property, a dormer is a structural extension to the existing roof which protrudes vertically from the plane or sloping roof. Internally, a dormer has vertical walls and a horizontal ceiling. Most of the construction work is conducted externally using scaffolding at the front and rear of the house- this means that there’s less disruption to the rest of the property. Dormers are versatile as they can be built on different styles of homes, including terraced houses, end of terrace, semi detached and detached houses. Dormers can accommodate windows as well as French doors. 

There are different types of dormer loft conversions including:

  • The flat roof dormer is a simple structure that can be added to the front and/or rear of the loft. The plane of the roof is horizontal. This type of dormer provides the most space and floor area inside the building.
  • Gabled dormers have a peak at the top and a roof that slopes downward on either side. The gable dormer is so called because its roof design is the same as that of a regular gable roof and usually has a matching slope.  
  • A hipped roof dormer is an extension to an existing roof with a pitch on three sides. Usually on semi detached or end of terrace properties, these conversions will feature a vertical dormer wall on the side and rear of the property to gain maximum space.
  • Similar to a rear dormer but offering more square footage, an L-shaped dormer typically involves constructing two dormers – one sits on the main body of the house and the other then extends out over the rear addition of the property. So, the dormers meet to create the ‘L’ shape. An L-shaped dormer can only be carried out on certain properties. Often converted are Victorian properties where the kitchen and bathroom are located in the back addition of the rear property. 
A rear dormer

Will you need planning permission?

Generally, if you meet your borough's criteria, a dormer loft conversion can be carried out under permitted development (with no need for planning permission). However, it's important to be aware of the specific conditions and limitations of permitted development. If you are unsure as to whether your proposed conversion passes the permitted development tests, we recommend obtaining a Certificate of Lawful Development (COL), from your local authority. If you wish to sell your property in the future, for example, this acts as a safeguaed as it provides you with written proof that your loft conversion is lawful.

An L-shape dormer

However, you will need Planning Permission if:

  • The height of the proposed dormer extension will exceed the height of the existing roof.
  • The volume of the new addition exceeds the limits of permitted development. The limits are currently 40 cubic metres for terraced houses, and 50 cubic metres for both detached and semi-detached houses. These limits apply to the size of the ‘Original House’ which refers to the house as it was on 1st July 1948, or if your property was constructed after this date, the size of the house when it was first built.
  • The dormer loft conversion includes a balcony, veranda or raised platform.
  • The loft conversion includes side facing windows overlooking neighbouring properties. To fall within the conditions of permitted development, any side facing windows must be obscured glass, and only able to open at a height of 1.7 metres above the floor of loft room.
  • The proposed dormer extension reaches less than 20cm from the original eaves when measured along the roof plane.
  • The materials you plan to use in the construction of your loft conversion are not in keeping with the appearance of the existing house.
  • A loft conversion does not fall into the category of permitted development if a property situated within an area of outstanding natural beauty, conservation area, national park or world heritage site.

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