Div. B › Part 9 › 9.21 › 9.21.4 — Masonry and Concrete Chimney Construction

9.21.4.8 — Wall Thickness

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(1) The walls of a masonry chimney shall be built of solid masonry units not less than 70 mm thick.

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chimney

means a shaft that is primarily vertical and that encloses at least one flue for conducting flue gases to the outdoors.

solid masonry

means a single-wythe or multi-wythe construction made of solid masonry units or semi-solid, cored or hollow masonry units, the cells of which may or may not be filled with mortar or grout. In multi-wythe masonry construction, the space between the wythes consists of a mortar-filled collar joint or grout-filled space and the wythes may or may not be constructed of the same masonry materials.

solid masonry unit

means a concrete block or brick unit, a clay brick unit or a calcium silicate brick unit, the net solid area of which is at least 75% of its gross area.

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