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Re: Structural wood beam support on a chimney

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I was under the impression that chimneys/flues should never be used for any structural support, but a review of IRC2003 shows that you can, as long as they're designed for the load (R1001.5). There doesn't appear to be an allowance for combustible material bearing within the envelope of the chimney. So you might use a face connection if you meet UL1777, or if you can make the masonry chimney part of a "wall" (3:1, right?), in which case you can bear provided you're more than 12" from the interior of the flue. Or you can design the chimney to support the load and put in a steel beam to be trimmed appropriately. Don't forget that a hard connection to the masonry will make the chimney a significantly stiff element in the lateral force resisting system, and it should be designed to carry the lateral loads (wind, I would assume) for that side of the building.

Jim Wilson wrote:
IRC 2003 R1001.15 Chimney Clearances requires a 2" clearance from combustibles. But the first exception permits combustibles to be in contact with the chimney provided that the chimney is lined in accordance with UL1777. Is the same true for supporting a wood beam in a beam pocket in a chimney? The pocket would be so detailed to maintain any required dimensional offsets and clearances from the liner and chimney box, perhaps by providing a double masonry wall at this point. Background: A client wants to add a stone-faced chimney centered in a gable wall with a structural ridge beam over a cathedral space. The chimney will stick into the room approximately 12". There is no place else to support this beam, other than on the masonry. A wood beam "header" could have to cross behind the stone facing, which isn't too practical. Jim Wilson, PE
Stroudsburg, PA

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