The new codes require safe clearances between masonry and combustible materials but with specific exceptions that allow for safe ways of closing combustible walls around masonry fireplaces. The codes also allow combustible material to be in contact with masonry chimneys that are part of masonry wall systems, provided that the combustibles are at least 12 inches from any interior firebox or flue lining.
Both codes permit Rumford fireplaces and masonry heaters, and provide guidelines concerning their construction and safety. The chimney and fireplace code requirements are essentially the same; however, the IBC, contains additional sections on medium- and high-temperature chimneys in nonresidential buildings. This article focuses on residential fireplace and chimney requirements.
The IRC states that, with three exceptions, there must be at least 2 inches of air space between combustible materials and any portion of a masonry chimney. The minimum clearance to combustibles is reduced to 1 inch for chimneys located entirely outside of a building's exterior walls, including chimneys that pass through a soffit or cornice.
The IRC also states that wood beams, joists, studs, and other combustible framing materials must have an air-space clearance of at least 2 inches from a masonry fireplace. Four exceptions are allowed.
Efficient and clean-burning, Rumford fireplaces are permitted with certain provisions.
In a masonry heater, the flow path downstream of the firebox must include at least one 180-degree change in flow direction before entering the chimney. The exterior masonry surface of the heater must not exceed 230° F except within 8 inches surrounding the fuel-loading doors. There must be a 4-inch clearance between wood or other combustible framing and the outside surface of a masonry heater when the walls of the firebox are at least 8 inches thick and the walls of the heat-exchange channels are at least 5 inches thick. There must be a minimum clearance of 8 inches between the heater's gas-tight capping slab and a combustible ceiling. The required space between the heater and the combustible material must be fully vented to allow the free flow of air around all heater surfaces.
The code changes represent an important victory for the Masonry Alliance for Codes & Standards, the Clay Flue Lining Institute, the Masonry Heater Association of North America, the Hearth Products Association, and the National Chimney Sweep Guild, among others.
The International Building Code and the International Residential Code will be published in April 2000 and ready for adoption by the various state and local governments that are charged with code enforcement. Meanwhile, the code change process continues, and there will be opportunities to propose further changes in future years.
This article also describes the evolution of the codes from the post-World War II building boom.