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American Wood Council

Courtesy of LEVER Architecture

Tall mass timber is an industry term to identify mass timber buildings, constructed of mass timber elements, that exceed current height limits for wood buildings set by the International Building Code. Mass timber includes any product currently permitted for use in Type IV construction, such as Cross Laminated Timber, Structural Composite Lumber, glued-laminated timber, and large section sawn lumber.

Because of the unique structural and fire resistance characteristics of solid timber walls and floors (CLT) and mass timber structures, in 2016 the International Code Council appointed a balanced committee of building officials, fire officials, architects, fire protection engineers, and industry experts to examine and propose appropriate code requirements. The committee’s work can be followed at this link: ICC Ad Hoc Committee on Tall Wood Buildings

2021 IBC Proposed Code Change Resources

Building Officials Guide to Tall Mass Timber Code Changes

14 Tall Mass Timber Code Changes Recommended for Approval

  • IBC Section 602.4 Type IV construction (G108-18)
  • IBC Section 703.8 Tested noncombustible protection contribution (FS5-18)
  • IBC Section 722.7 Calculated noncombustible protection contribution (FS81-18)
  • IBC Section 703.9 Sealing of adjacent mass timber elements (FS6-18)
  • IBC Section 718.2.1 Fireblocking materials (FS73-18)
  • IBC Section 403.3.2 High rise sprinkler water supply (G28-18)
  • IFC Section 701.6 Owner’s responsibility (F88-18)
  • IFC Section 3314.7 Fire safety during construction (F266-18)
  • IBC Table 504.3 (G75-18)
  • IBC Table 504.4 (G80-18)
  • IBC Table 506.2 (G84-18)
  • IBC Section 3102.3 Special construction (G146-18)
  • IBC Appendix D Fire Districts (G152-18)
  • IBC Sections 508.4.4.1 and 509.4.1.1 Fire barriers at separated occupancies and incidental uses (G89-18)

2021 IBC, 2018 Group A, Tall Mass Timber Proposals Review Guide

Tall Mass Timber Courses

Available AWC eCourses

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eCourse for CEU
  • DES600 – Tall Wood Structures: Current Trends and Related Code and Standard Changes

  • DES602 – Tall Wood Structures: Fire Resistance Design Primer for Mass Timber Construction

  • DES602-1 – Fire-Resistance Design Primer for Mass Timber Construction

  • DES603 – Fire Tests in Support of Tall Mass Timber Buildings

  • DES604 – CLT Adhesive Tests in Support of Tall Mass Timber Buildings

  • DES605 – Outcomes of ICC Tall Wood AdHoc Committee: Proposals and Discussion

  • DES606 – Experiences of a Mass Timber Builder

Mass Timber Fire Testing

ATF Compartment Fire Tests

A team of fire experts from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) working alongside scientists from the U.S. Forest Products Laboratory put identically furnished, multistory, one-bedroom apartments constructed of exposed, partially exposed, and unexposed (protected) five-ply cross-laminated timber (CLT) through a series of rigorously monitored fire tests. The tests provided valuable data that was used in the development of code change proposals submitted by the ICC Ad Hoc Committee on Tall Wood Buildings (TWB) for the 2021 International Building Code. A series of five tests were conducted. Each test was designed to replicate real world conditions across five scenarios. Identical, furnished, one bedroom apartments were constructed in a multistory building. The door between the living and sleeping areas was left open in both apartments. A three minute video capturing the highlights of each test is included in this playlist.

Full-Scale Fire Tests of a Two-Story Cross-Laminated Timber Structure Report


ASTM E119 Wall Test Summary



Fire Safety and Protection: During the planning, construction, and occupancy of a building, fire safety is a priority.


Tall Mass Timber News
Code Connections

Code Official Connections is free to qualified governmental employees and is designed for the professional needs of the code administration and enforcement community.

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Building Codes

On behalf of the industry it represents, AWC is committed to ensuring a resilient, safe, and sustainable built environment. To achieve these objectives, AWC contributes to the development of sound public policies, codes, and regulations which allow for the appropriate and responsible manufacture and use of wood products. We support the utilization of wood products by developing and disseminating consensus standards, comprehensive technical guidelines, and tools for wood design and construction, as well as providing education regarding their application.

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Fire Safety

Resources for code and fire officials on fire performance of wood products.

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