Mansard conversions can be described as a roof extension across the entire span of the roof, end to end. First the head height is increases by building a structure much like a dormer, only a mansard with span the entire width, will have a flat roof that meets the ridge line and has a sloping side dropped to a near vertical. Small Window Dormers are added and inset to the structure. For end of terrace conversions we also build up the outer sidewall/s in matching brickwork to for a sympathetic look with the exiting building. Mansards can be chosen for this synergy between old and new, but can be added to any building where this design is preferred and where it is insisted upon due to restrictions by the local authority. The real benefit is that this shape can give up to a 10-fold increase in space to that of a standard Dormer conversion.
In addition, as with L-shaped Dormers, an L-shaped Mansard can be created to take advantage for the addition space on your roof to create of of the largest conversions available to most homeowners.