Dormers Dormers Generally a high ridge can accommodate a modest sized dormer room. Problems can arise, however, when the design and/or layout of the existing house is unsuitable because of the angle of the ridge or because it would overlook habitable rooms in a neighbouring property. In such cases an alternative form of extension should be considered. On the front elevations of properties particular care is needed to ensure that any dormer window or dormer extension does not effect the street picture. On semi-detached and terraced properties it is unlikely that dormers would be acceptable. Dormer windows in roofs should complement the existing features of the dwelling in terms of its proportions, size and positioning. Generally dormers should be constructed in materials to match the existing dwelling. Dormers too high in the roof, which would cause the loss of the ridge line when viewed from the street, or the creation of very long dormers, particularly on terraced or semi-detached properties should be avoided. Where extra headroom is not required roof lights offer a simple, economical method of lighting the roof space. They are best kept as small as possible so as not to dominate the roof space.