Proposed changes to the IBC: 2021 edition
Tall wood buildings, such as the 18-story Brock Commons student residence at the University of British Columbia in Vancouver, have been announced or recently opened in North America and Europe as a result of increased interest in sustainable construction materials and reducing the carbon footprint. The design and construction of “mass timber” buildings in various U.S. cities have been approved by the local authorities on a case-specific basis. To provide a uniform, consensus-based approach to the requirements for these buildings, the International Code Council (ICC), publisher of the International Building Code (IBC), established the Ad Hoc Committee on Tall Wood Buildings (TWB) in 2016. The goal is to develop comprehensive design and construction criteria to be proposed for the 2021 edition of the IBC. The TWB is working toward a Jan. 8, 2018, deadline for the code-change proposals.
Committee for tall wood buildings
The TWB committee consists of architects, engineers, building officials, fire officials, and construction industry and testing agency representatives. In addition to the technical committee, more than three dozen other interested parties have been participating in the process. Since the summer of 2016, the TWB has reviewed technical literature, the available technology, fire loss history, and recent fire tests and is currently drafting proposed language for the 2021 IBC. The TWB has undertaken a comprehensive review of every chapter of the IBC to determine the effect of allowing taller and larger wood buildings on the safety of the built environment.
Two principal concerns of the TWB are: 1. the impact of the increased fuel load contributed by the wood structure to a building fire; and 2. the combustibility of the structural members, which could lead to failure of the structure before building evacuation and interior firefighting is completed — a life safety risk, as well as the potential for property damage to adjacent properties. A number of specific concerns are being addressed. These include attention to the connections between the structural elements, and the various types of adhesives that are used to assemble cross-laminated timber and other products which, together with traditional “heavy timber” members, are being called “mass timber construction” in the current draft.
Proposed changes to the IBC
Two series of full-scale fire tests, one conducted by the NFPA Research Foundation and one conducted by the American Wood Council (AWC), have contributed valuable information to the work of the committee. The NFPA Research Foundation tests were conducted without fire sprinklers and were intended to determine the performance of various layers of gypsum board protection for the wood structure as well as the effects of various ventilation openings. The AWC tests included both unsprinklered and sprinklered cases to determine the effects of gypsum board protection, ventilation, and sprinklers for both a “normal” case and one with a delayed water supply. The data from these two series of tests are currently being analyzed, and the findings will be formally presented to the TWB in reports later this year.
The working draft of the TWB currently includes four types of mass timber construction. Type IV-HT construction is identical to the current Type IV Heavy Timber construction in the IBC. The working draft also includes three new subcategories: Types IV-A, IV-B, and IV-C construction, with each having various ratings of 3-hour, 2-hour, and partially exposed wood structural members within these three types of construction, with IV-A having the highest rated structure. The proposal recognizes that exposed wood members can be designed (oversized) to sustain a fire and remain standing; however, at least two-thirds of the required rating for types IV-A and IV-B construction must derive from noncombustible passive protection. Similarly, while automatic sprinkler protection will be a key element of the building’s protection features, the committee believes that tall wood buildings should have a major portion of the structural fire resistance provided by passive means.
As with other types of construction, the current concept is that the IBC will allow taller and larger mass timber buildings as the passive fire-resistance ratings are increased from one subcategory to the next. Other specific provisions will address combustible concealed spaces, shaft construction, and exterior wall combustibility.
The proposed code change will be first considered at a public hearing scheduled for April 2018 in Columbus, Ohio.
Carl Baldassarra is a principal at Wiss, Janney Elstner and Associates and leads the consulting engineering firm’s fire protection practice group. He has a bachelor’s degree in fire protection engineering and a master’s degree in business. He is a licensed engineer in several states.Mr. Baldassarra leads project teams involving fire protection/life safety analysis, code consultation, fire protection system design, loss investigation, and litigation support. He also is very active in a number of ICC and NFPA codes- and standards-making technical committees. He was chair of ICC’s Code Technology Committee as well as a member of that committee for its 10-year duration. Most notably for this article, he is a member of the NFPA Fire Protection Research Foundation Technical Advisory Panel for Tall Wood Buildings and a member of the ICC’s Ad Hoc Committee on Tall Wood Buildings.