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CHIMNEY INFORMATION & REGULATIONS (Cont.)
Factory-Built Chimneys
Depending on the manufacturer and where the chimney is to be installed, special supports, roof
assemblies, radiation shields, or locking bands may be supplied as a part of the chimney system. The
manufacturer's installation instructions, which are reviewed by the listing agency, specifies when and
where each of these components must be used.
There are three standard installations with factory-built chimneys. Each type of installation should use
flashing and an adjustable storm collar at the roof line to prevent water from entering the house.
Manufacturers require that chimneys extending beyond a certain height above the roof (frequently above
5 feet) must also be braced.
A chimney cap keeps out rain, birds and other animals, and may reduce down drafts. Spark arresters,
wire mesh devices designed to catch sparks and burning particles emitted with the smoke, may be
included with factory-built chimney caps. These spark arresters may become encrusted with creosote,
blocking the proper flow of flue gases out of the chimney. When burning wood, it is recommended that the
spark arrester be cleaned regularly, or removed entirely unless individual conditions or local codes
require their use.
Determining the Distance Between the Chimney and Combustibles
The chimney must be kept a minimum distance of 2" away from combustibles (e.g., drywall, wood framing,
etc.). The distance between the outside surface of a chimney and combustibles is measured horizontally,
at right angles to the chimney. The pitch of the platform (e.g., the roof) must be considered in calculating
the size of the hole that is cut.
Calculating the Cut-Out on a Slanted Roof
Combustible Roof
Factory-Built Chimney with
Required 2" Clearance
Length of Cut-Out in Roof
2" Min.
c
a
b
90û
Width of Cut-Out in roof
= 4" + chimney width
Length of Cut-Out in Roof
= "c" times 2 + chimney width
Width of
Cut-Out in Roof
