Over the past 10 years, there has been growing interest in tall buildings constructed from mass timber materials as a means to achieve greater urban density with more sustainable construction. Worldwide, there are now dozens of wood buildings more than eight stories tall.
In the U.S., the 2021 International Building Code (IBC) includes three new construction types—Type IV-A, IV-B and IV-C—that allow the use of mass timber or noncombustible materials in buildings up to 18, 12 and nine stories (respectively). These construction types are based on the previous Heavy Timber construction type (Type IV, changed to IV-HT in the 2021 IBC) but with additional requirements regarding fire-resistance ratings and use of noncombustible protection.
Mass timber projects designed under the 2018 or earlier versions of the code are generally constrained by prescriptive building height limits of five to six stories depending on the occupancy group. The term “tall timber” is associated with buildings that exceed the limits of previous codes for number of stories, height and in some cases area.
If you’re interested in pursuing a tall timber project in the U.S., see below for commonly asked questions and resources. WoodWorks also provides free technical support to developers and design/construction teams. For assistance, contact the WoodWorks Regional Director local to you or email email@example.com.
Tall Timber FAQs
1. What is the current status of tall mass timber buildings in the building code?
Follow this link for status of the 2021 IBC and jurisdictions that have adopted the tall wood code provisions.
2. What are the height limits for the new construction types?
3.What are the timber exposure limits for Types IV-A, IV-B, IV-C and IV-HT construction
4. What are some U.S. projects that have used the 2021 IBC tall mass timber options?
- Carbon12 – Portland, OR
- INTRO – Cleveland, OH
- Ascent – Milwaukee, WI
- 80M – Washington, DC
- Apex Clean Energy – Charlottesville, VA
- 11 E Lenox – Boston, MA
- Mass Timber Workforce Housing – Seattle, WA
Visit the WoodWorks Information Network for a searchable map of mass timber projects across the U.S. (and beyond), and to learn about their project teams.
5. What are the fire-resistance rating requirements for tall mass timber?
Technical Design Guidance
- Tall Wood Buildings in the 2021 IBC – Up to 18 Stories of Mass Timber
- Demonstrating Fire-Resistance Ratings for Mass Timber Elements in Tall Wood Structures
- Shaft Wall Requirements in Tall Mass Timber Buildings
- Concealed Spaces in Mass Timber and Heavy Timber Structures
- Acoustics and Mass Timber: Room-to-Room Noise Control
- Fire Design of Mass Timber Members: Code Applications, Construction Types and Fire Ratings
- Tall Timber Buildings: Where Structural Engineering Meets Fire Engineering
- Technical Report 10: Calculating the Fire Resistance of Wood Members and Assemblies
- Contact your local WoodWorks Regional Director for educational offerings on tall mass timber design, including seminars and lunch and learns
- Recorded webinar: A Tale of Two Timber Towers
- Recorded webinar: Seattle Mass Timber Tower: Envisioning 12 Stories of Wood
Codes and Standards
- What is the current status of tall mass timber buildings in the building code?
- American Wood Council
- 2021 International Building Code
- Mass Timber Buildings and the IBC
- National Design Specification® (NDS®) for Wood Construction
Testing, Research and Feasibility Studies:
- Inventory of Acoustically-Tested Mass Timber Assemblies
- Inventory of Fire-Tested Mass Timber Assemblies, Penetrations & Connections
- Fire Safe Implementation of Mass Timber in Tall Buildings
- Compartment Fire Testing of a Two-Story Mass Timber Building
- Tall with Timber: A Seattle Mass Timber Tower Case Study
- Mass Timber High-Rise Design Research: Museum Tower in Los Angeles Reimagined in Mass Timber
- Survey of International Tall Wood Buildings
- Timber Tower Research Project