Chimneys should be built in cement mortar, and in order to render the flues as dry as possible, they should be surrounded with walls one brick in thickness. A damp-proof course just above the junction with the roof should be provided, so as to prevent rain-water soaking through to the roof timbers.
The stacks should be carried up at least three feet above the ridge of the roof, and the flues gathered over, as shown in picture 29, in prevent the tendency to down draughts, which arises when the chimney - pot and fireplace are in the same vertical line.
There are many patent chimney-pots and cowls for the cure of chimneys that will not draw properly, and in low-lying sites we have found some to be of service, but the secret of a good draught lies mainly in the skilful construction of the flues themselves.
The general architectural treatment of chimneys is considered in chimney design.
Picture 29. The Gathering of Flues.
Next: Floor Construction.