This style of loft conversion is best for properties where the existing roof space would provide insufficient headroom in the finished room.
It involves creating additional space by extending the walls up through the roof a short way (usually only on one side) to create a flat ceiling inside.
This makes the new room more practical, especially if you wish to incorporate an en-suite bathroom for example. There are several types of Dormer loft conversion available, including flat roof, hipped and pitched.
Cjs lofts will advise you of the advantages of each style.