Yes, a dormer conversion is perfectly possible on terraced, semi-detached and detached houses – provided, that is, that it meets fully with planning permission and building regulation guidelines. A dormer adds floorspace to an extension, as well as height. That’s because it extends the existing sloping roof into a ‘box-like’ structure ie it has a horizontal ceiling and a vertical wall (rather than a sloped one). L-shaped dormer conversions are very possible these days. A dormer can be flat-roofed, gable-fronted, come with a hipped-roof or be a shed-dormer (still a vertical roof but not at such a pronounced angle as the main roof).