From ASTM C 1283 .... 8. Chimney Caps 8.1 All masonry chimneys shall have a chimney cap that slopes a minimum of 10 degrees downward from the flue liner to the edge of the chimney cap (see Fig. 1). 8.2 Chimney caps shall overhang the chimney wall by a minimum of 2 in. (51 mm).

FIG. 1 Chimney Cap

8.3 Chimney caps are of the following types and construction: 8.3.1 Precast or cast-in-place concrete caps shall be a minimum of 2 in. (51 mm) in thickness, shall have a drip slot on the underside at least 1 1/2 in. (38 mm) away from the chimney wall, and shall be reinforced with a minimum of 1/2 in. (13 mm) mesh galvanized hardware cloth located halfway into the filled form. 8.3.2 Metal chimney caps must lap down the chimney wall at least 4 in. (100 mm) and a noncombustible resilient sealant shall be used between the metal cap and the flue liner and between the base of the metal cap and the chimney. 8.3.3 Stone caps shall be a minimum of 2 in. (51 mm) in thickness and shall have a drip slot on the underside at least 11/2 in. (38 mm) away from the chimney wall. 8.4 Chimney caps shall be separated from the flue lining by a bond break, and this separation shall be sealed with a noncombustible resilient sealant to prevent water entering the chimney. This is a maintenance joint and should be checked and renewed as needed (see Fig. 1). 8.5 Clay flue linings shall extend above the chimney cap by not more than 4 in. (100 mm). 8.6 Where a clay chimney pot is installed on a masonry chimney, the chimney pot shall comply with the requirements of Specification C315.

Chimney Cap Code Change Proposal - R1003.9
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