Code Corner: Exception for Fire Rating of Roof Structure Update
When building of Type 1A, 1B, 2A. 3A, or 5A construction, per Table 601, there is a requirement that the roof construction and associated secondary members are to have a fire-resistance rating of 1 ½ or 1 hour rating, depending upon the construction type that is to be used.
Those who are familiar in using Table 601 may recall that this section for roof construction is then modified by footnote “b,” which states that except for Use Group F-1, H, M and S-1 occupancies, fire protection of structural members shall not be required, including protection of roof framing and decking where every part of the roof construction is 20 feet or more above the floor immediately below. This is commonly known as the 20 feet exception in the code. This exception is often used in spaces that have high roofs, such as churches and assembly spaces. Most recently, the University of Findlay Student Center and College of Business building utilized this exception for its large open space that utilized long span bow trusses. This exception allows for reduced cost and an aesthetic design free of either spray-on fire proofing or gypsum board protection of roof assemblies.
However, over the years, there have been inconsistencies from building department to building department as to what may be exempted by footnote “b” of this exception. Are large girder trusses that make up the roof exempted? What about the columns that may support the roof? Are they exempt as well? Or do you need to fire rate them up to a height of 20 feet, and then from that point and above are you allowed to drop out the fire rating of the columns?
Due to the uncertainty of this section, the International Code Council (ICC) has recently issued a formal interpretation that finally addresses the various interpretations of this section as follows: “Footnote “b” to Table 601 was modified in the 2018 IBC to state that fire protection of structural members in roof construction shall not be required, including protection of primary structural framing members, roof framing and decking and decking where every part of the roof construction is 20 feet or more above the floor immediately below."
By expanding the scope of the footnote to include primary structural frame members, it is now clear that all portions of the roof construction are exempt (e.g. beam and girder). But at the same time, this definition solidifies that a rating would still be required for any columns that support the roof structure, since columns clearly do not fall into the scope of roof construction. Therefore, columns that are utilized in any of the fire rated construction types noted above will be required to be fire rated that support a fire resistive rated roof construction, regardless of the height of the roof assembly above the floor.
by Jim Mitchell
Principal, Executive Vice President, Director - Civic/Community Studio
As a registered architect for over 27 years and a State of Ohio Certified Master Plans Examiner and Chief Building Official, Jim is a wealth of knowledge regarding building codes. His favorite place to eat is Polaris Grille, and his favorite movie is National Lampoon's Christmas Vacation.