Dormers

Before 1550 thatched roofs were relatively simple in design. Changes to the design of the roof and roofs built after 1550, when chimney stacks projected through the roof and the upper floors become increasingly smart and well-lit, made the work of the thatcher more complicated.

Half dormers in Britain are common. These windows are partly in the wall but project above the line of the eaves. In early houses they are often enlargements of smaller windows, or new windows to make the first floor rooms better lit and ventilated.

So long as the windows are not too tall, the thatch over half dormers can be 'eybrowed', thatched over in a sweep that rises above the eaves and joins the main pitch of the roof without any valleys. Taller half dormers, or full dormers (where the sill of the window is at the line of the eaves) project too far above the plane of the roof to be eyebrowed, and are usually thatched separately.

Roof dormers, windows where the sill is above the line of the eaves and the whole construction of the window is within the slope of the roof are virtually never found as original features in British traditional buildings.