Buckley Rumford Fireplaces
2013 IRC Code Change Proposal RB458

RB458 - 13

Proponent: Jim Buckley, Buckley Rumford Co. representing Masonry Alliance for Codes and Standards and Clay Lining Institute (buckley@rumford.com)

Revise as follows:

R1003.18 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum air space clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum air space clearance of 1 inch (25 mm). The air space shall not be filled, except to provide fire blocking in accordance with Section R1003.19.


    1. Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777 and installed in accordance with the manufacturer's installation instructions are permitted to have combustible material in contact with their exterior surfaces.

    2. When masonry chimneys are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete wall less than 12 inches (305 mm) from the inside surface of the nearest flue lining.

    3. Exposed combustible trim and the edges of sheathing materials, such as wood siding and flooring, shall be permitted to abut the masonry chimney side walls, in accordance with Figure R1003.18, provided such combustible trim or sheathing is a minimum of 12 inches (305 mm) 8 inches (203 mm) from the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of the chimney by more than 1 inch (25 mm).

Reason: Tests have shown that the currently required 12" chimney wall thickness for the chimney to be in contact with combustible trim is overly restrictive. Chimneys with enclosing walls of 8" in contact with combustible material are at least as safe as the current basic code requiring chimneys to have 4" thick solid masonry walls two inches clear of combustibles. This change would provide for timber frame or wood ceilings to safely abut a masonry chimney.

Eight Inch Chimney Wall Test

Cost Impact: The code change proposal will not increase the cost of construction, it would reduce the cost.


Public Hearing: Committee: AS Assembly: WP


Andy Klein's Eight Inch Chimney Wall Test Report not only presented the test results in a professional maner but added an engineering simulation to confirm the test results and shed light on the long-standing argument about whether or not to fill the 2" air psace with insulation. The test report was delivered to the IRC committee since it was received too late to include in the original proposal submission.

The proposal had the support of MACS and, becasue of the test report, the NAHB and the NCHBA.

With this support, the IRC Committee approved the proposal ten to zero as submitted. Gary Ehrlich, NHBA, gave strong endorsement lauding test. So did a NCHBA builder.

The National Association of State Fire Marshals submitted a comment asking for disapproval due to inadequte justification but after they read the Test Report and checked with the NAHB, Kelly Nicolello, representing th fire marshals, agreed to withdraw their comment which meant that the issue would not be discussed by the Assembly and the proposal would stand as approved as submitted by the IRC Committee.

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