In the 2021 I-codes, what are the requirements pertaining to fire-resistance ratings of mass timber connections?


There are no specific code requirements or allowances in the IBC for determining the fire resistance of a connection itself. In fact, there are no code-prescribed means of establishing the fire resistance of a connection by itself. The standard fire-resistance tests referenced in the IBC (ASTM E119 and UL 263) do not provide the necessary protocol for testing a connection configuration in the furnace. However, the IBC does require fire protection of connections, and this protection must consist of materials that provide a fire-resistance rating not less than that required of the connected members. Specifically, IBC Sections 704.2 and 704.3 make explicit reference to the requirement for fire protection of connections as follows:

704.2 Column protection. Where columns are required to have protection to achieve a fire-resistance rating, the entire column shall be provided individual encasement protection by protecting it on all sides for the full column height, including connections to other structural members, with materials having the required fire-resistance rating. Where the column extends through a ceiling, the encasement protection shall be continuous from the top of the foundation or floor/ceiling assembly below through the ceiling space to the top of the column.

704.3 Protection of the primary structural frame other than columns. Members of the primary structural frame other than columns that are required to have protection to achieve a fire-resistance rating and support more than two floors or one floor and roof, or support a load-bearing wall or a nonload-bearing wall more than two stories high, shall be provided individual encasement protection by protecting them on all sides for the full length, including connections to other structural members, with materials having the required fire-resistance rating.

It should be noted that these code sections are not specific to any particular construction type or construction material; so they apply to connections in steel construction, concrete construction, and the new mass timber construction types alike. That said, most of the members in traditional heavy timber construction (now called Type IV-HT) are not required to meet an explicit fire resistance rating, so the connections between these members are not necessarily required to be protected.

For connections between structural members in the new mass timber construction types (Types IV-A, IV-B and IV-C), the protection time provided by the fire protection to be applied over the connection must be determined based on a standard fire exposure. Section 703.3 provides the various methods that are permitted for establishing the fire-resistance rating of building elements, component or assemblies based on a standard fire exposure.  These are as follows:

  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 determined 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.

The procedure for protecting connections provided in AWC Technical Report No. 10 (TR10) (https://awc.org/codes-standards/publications/tr10) is based on the results of ASTM E119 tests, particularly as it pertains to the char rate of wood and/or the performance of gypsum wallboard. Thus, these TR10 provisions for protecting connections with wood and/or gypsum wallboard provide a means of determining fire resistance that is in compliance with item 4 of IBC Section 703.3.