Any openings in chimneys should consist of a metal thimble around which the brickwork is carefully laid and cemented. Boiler clay or putty should be used to make any loose smokepipe connections air-tight.
WALL STRUCTURE
The walls of both exterior and interior chimneys without linings, and exposed walls of exterior chimneys, must be at least eight inches thick The walls of the interior chimney with flue linings must be at legist four inches thick. Interior chimneys should have eight-inch walls from below the roof to the top. Flue linings should be separated by brick divisions or withes at least four inches in width- The walls of stone chimneys should be at least 12 inches thick.
CHIMNEY AND ROOF
Careful consideration should be given to the proper connection between chimney and roof. This is one of the principal points at which a fire can start. Therefore, at least a two-inch clearance should be provided for between the wood framing and the masonry. This will also allow for expansion or movement of the chimney due to temperature changes or strong winds
CAPPING
A chimney cap should always be provided so ;is to reduce chimney maintenance. The top surface of the cap should slope upwards to the flue to provide water drainage, and to deflect air currents upward as they pass the chimney top. When a hood is used, the area of the hood opening should be at least equal to to the area of the flue. Concrete and brick caps are usually made four inches thick, and it is advisable to project them an inch or two to form a drip ledge
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