A dormer conversion is typically built when full-height space must be added to your loft. This type of extension to the roof line varies in size and can be flat or gabled. If you plan to put a dormer window on the front of your home or overlooking a highway, you will need to apply for planning permission as this conversion structurally and visually alters your house. Rear dormers are the most popular conversion approach. They offer great flexibility in the choice of rooms possible within the loft space. Rear dormers can be constructed on most terraced and semi-detached properties.