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august 2019 csengineermag.com 35 The requirements of Type IV construction to have no concealed spaces in floors or roofs and for all interior partition walls to be solid wood or 1-hour rated can significantly impact its utility for some applications. The alternative of using Type III construction (or Type V where building size permits) avoids this limitation; however, the processes for demonstrating fire-resistance ratings also vary between Type IV and Types III and V. Methods for meeting fire-resistance rating requirements for mass timber elements in buildings other than Type IV construction are the focus of the rest of this paper. Methods to Demonstrate Fire-Resistance Ratings of Mass Timber When a mass timber building element or assembly is required to have a fire-resistance rating, IBC Section 703.2 requires the rating to be determined by testing in accordance with ASTM E 119 (or UL 263) or via one of six alternatives listed in IBC Section 703.3: The required fire resistance of a building element, component or assembly shall be permitted to be established by any of the following methods or procedures: 1. Fire-resistance designs documented in approved sources 2. Prescriptive designs of fire-resistance-rated building elements, components or assemblies as prescribed in Section 721 3. Calculations in accordance with Section 722 4. Engineering analysis based on a comparison of building element, component or assemblies designs having fire-resistance ratings as deter- mined by the test procedures set forth in ASTM E119 or UL 263 5. Alternative protection methods as allowed by Section 104.11 6. Fire-resistance designs certified by an approved agency These alternatives are options when the exact assembly has not been tested per ASTM E 119 and a test report is therefore not available. They are all founded on ASTM E 119 testing. There are currently limited options for fire resistance-rated mass timber assemblies from approved sources (e.g., Gypsum Association GA-600, American Wood Council's Design for Code Acceptance 3 – Fire Resistance-Rated Wood Floor and Wall Assemblies, [DCA 3]) or certification agencies (e.g., UL listings). However, an increasing number of assemblies have been tested according to the ASTM E119 standard and are available publicly or on request from manufacturers. The number of available tested assemblies can be expanded using comparative engi- neering analysis described in Item 4 of IBC Section 703.3. Such an analysis, which seeks to justify the fire-resistance rating of an assembly or component similar to one that has passed an E119 test, can be performed by a fire protection engineer. Item 3 of IBC Section 703.3, which permits the use of calculations in accordance with Section 722, is also frequently used to demonstrate the fire-resistance rating of exposed mass timber. IBC Section 722.1 states: The calculated fire resistance of exposed wood members and wood decking shall be permitted in accordance with Chapter 16 of ANSI/AWC National Design Specification® for Wood Construction (NDS®). Chapter 16 of the NDS can be used to calculate up to a 2-hour fire-resistance rating for a variety of exposed wood members including solid sawn, glulam, SCL, and CLT. ASTM E119 Testing Method According to Section 4.2 of ASTM E119-18, the fire test procedure is intended to do the following: The test exposes a test specimen to a standard fire controlled to achieve specified temperatures throughout a specified time period. When required, the fire exposure is followed by the application of a specified standard fire hose stream applied in accordance with Practice E2226. The test provides a relative measure of the fire-test-response of comparable building elements under these fire exposure conditions. The exposure is not representative of all fire conditions because conditions vary with changes in the amount, nature and distribution of fire loading, ventilation, compartment size and configuration, and heat sink characteristics of the compartment. Variation from the test conditions or test specimen construction, such as size, materials, method of assembly, also affects the fire-test-response. For these reasons, evaluation of the variation is required for application to construction in the field. Successful fire tests have been completed on numerous mass timber elements and assemblies, achieving fire-resistance ratings of 3 hours or more. Additional tests by manufacturers and others are ongoing. Most tests are conducted according to ASTM E119 or its Canadian equiva- lent, ULC S101. Both utilize the same time-temperature curve and performance criteria and, as such, ULC S101 fire tests are usually acceptable to U.S. building officials. However, each project's building official should be consulted if choosing this design route. To help building designers compare options, WoodWorks has compiled a web-based inventory of completed mass timber fire tests. The Inventory of Fire Resistance-Tested Mass Timber Assemblies & Penetrations as new tests become available, and can be found at http://bit.ly/2FRwAPG.

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