What is the current status of tall mass timber buildings in the building code?

Status as of January 1, 2020:

The first of two groups of proposed code changes regarding tall mass timber buildings has been approved for the 2021 International Building Code (IBC). The review and voting process for the second group of changes is underway and will be completed in the fall of 2019. Oregon has preemptively approved the first group of changes through a Statewide Alternative Method, allowing tall wood buildings today, and Washington will formalize similar prescriptive allowances in early July. Other jurisdictions are considering tall wood buildings through Alternate Methods and Materials Requests and/or allowing design teams to look ahead to the already-approved tall mass timber code language of the 2021 IBC, even though that version of the code has yet to be adopted in their jurisdiction.

Following is a more detailed summary of where things stand and how we arrived at this point:

The IBC is the model building code adopted in whole and/or with local amendments by most states and jurisdictions in the U.S. It is updated every three years to reflect advancements in products and technology while giving time to ensure that new additions provide adequate fire and life safety and structural performance and are fully vetted through a hearing, public comment and voting process. The current version is the 2018 IBC, and the 2021 IBC will be published in the fall of 2020.

In 2015, the board of the International Code Council (ICC), developer of the IBC, created the Ad Hoc Committee on Tall Wood Buildings (AHC-TWB) to assess the science behind mass timber high-rises and, if appropriate, propose changes to the code. After considerable review, the committee proposed two groups of changes—Group A and Group B—which are being reviewed and voted on sequentially. Key dates are as follows:

The Group A submission proposed 14 changes to the 2018 IBC, including three new construction types (IV-A, IV-B and IV-C), and changes related allowable building size, fire-resistance ratings, exposed timber, and fire safety during construction. The changes, which included aspects of general provisions (IBC-G), fire safety provisions (IBC-FS) and fire code provisions (IFC), are summarized below. The code change numbers are noted in parentheses.

Requirements for the new construction types:

  • IBC Section 602.4 – Type of Construction (G108-18)
  • IBC Section 703.8 – Performance Method for Fire Resistance from Noncombustible Protection (FS5-18)
  • IBC Section 722.7 – Prescriptive Fire Resistance from Noncombustible Protection (FS81-18)
  • IBC Section 703.9 – Sealants at Edges (FS6-18)
  • IBC Section 718.2.1 – Fire and Smoke Protection (FS73-18)
  • IBC Section 403.3.2 – High-Rise Sprinkler Water Supply (G28-18)
  • IBC Section 701.6 – Owners’ Responsibility (F88-18)
  • IFC Section 3308.4 – Fire Safety During Construction (F266-18)

Allowable building size limits:

  • IBC Table 504.3 – Building Height (G75-18)
  • IBC Table 504.4 –Number of Stories (G80-18)
  • IBC Table 506.2 – Allowable Area (G84-18)

Housekeeping changes:

  • IBC Section 3102 – Special Construction (G146-18)
  • IBC Appendix D – Fire Districts (G152-18)
  • IBC Section 508.4 and 509.4 – Fire Barriers (G89-18)

These changes received significant support throughout the Group A process in 2018, which included a Committee Action Hearing, online CAH assembly floor motion vote, public comment period, and public comment hearing. The Group A Online Governmental Consensus Vote took place in late 2018, and all of the proposals were approved—nine as submitted and five with modifications. (See this link for final results and the percentage of votes in favor and against). The final vote status was ratified by the ICC on January 31, 2019.

Effective with the 2021 IBC, the new construction types will allow varying degrees of exposed timber vs. wood with non-combustible protection. The largest prescriptively allowed mass timber building will be 18 stories and nearly 1 million square feet using Type IV-A construction. For more information regarding the Group A code changes, this document includes all of the final, approved tall mass timber-related code language and this WoodWorks paper describes the design impacts.

The Group B cycle, taking place throughout 2019, includes three additional changes to the administrative (Admin) and structural (IBC-S) provisions relative to tall mass timber buildings:

  • IBC Section 110.3.5 – Inspection requirements for connections that rely on wood cover for fire-resistance rating purposes (ADM 35-19)
  • IBC Table 1705.5.3 – Special inspection requirements for mass timber elements in Types IV-A, IV-B and IV-C (S100-19)
  • IBC Section 2304.10.1 – Prescriptive options for demonstration of fire resistance ratings of connections including mass timber elements in construction types IV-A, IV-B and IV-C (S170-19)

See this link for details on the Group B proposed changes.

All three Group B changes were approved as submitted during the CAH process, indicating that a simple majority vote during the OGSV in late 2019 will result in their approval. See the Group B CAH results here. Throughout the remainder of 2019, the AHC-TWB will monitor and respond to public comments regarding the Group B changes. There is currently no plan to have a Group C code cycle for the 2021 IBC.

Several jurisdictions have or are in the process of pre-emptively adopting tall wood-related code provisions, including:

For free project assistance related to the design of tall mass timber projects, or for general education related to the tall mass timber related code changes, contact the WoodWorks Regional Director local to you. For additional information on the safety of tall mass timber buildings, the work of the AHC-TWB in developing the code change proposals and other related topics, see resources available from the American Wood Council and the Mass Timber Code Coalition.