May 26, 2021
By Cheri Hanes, CRIS, LEED AP,
Head of Innovation and Sustainability, North America Construction, AXA XL
Mass timber is trending, and statistics show it is not likely to slow down anytime soon.
Many factors are driving this popularity: owners like it for the speed and potential cost savings, the higher rents it commands, and its alignment with their sustainability and other corporate social responsibility goals. Architects and designers love its beauty and the potential for new and exciting forms. Builders are enthused about the apparent simplicity of construction. Builders considering pursuit of a mass timber project need to account for many factors and make plans to take the right steps to deliver the project on time, on budget, and meet the owner’s expectations.
What is a mass timber project?
A Mass Timber Project is defined as a building construction project that incorporates structural elements of engineered wood products, as defined in the 2021 International Building Code (IBC), that meet minimum cross section dimensions for Type IV construction. This includes hybrid systems that also utilize concrete and/or steel elements along with Mass Timber structural elements.
As the proposed 2021 revisions to the IBC are adopted by local jurisdictions, the IBC designations will become more commonly used. The 2021 IBC classifies Mass Timber as Type IV construction with three sub-types that require varying amounts of encapsulation depending on building height:
- Type IV-A (all mass timber elements fully encapsulated and up to 18 stories)
- Type IV-B (protected exterior, partially exposed interior mass timber elements and up to 12 stories)
- Type IV-C (protected exterior, exposed mass timber interior and up to 9 stories)
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The code also retains Type IV-HT (No non-combustible protection required. 324,000 sf, 6 story maximum)
What are mass timber materials?
There are a variety of material types that fall under the Mass Timber umbrella, including Cross Laminated Timber (CLT), Nail Laminated Timber (NLT), Dowel Laminated Timber (DLT), Glue Laminated Timber (GLT), and more – with more types in development all the time. These materials all share many risk factors, and therefore all have similar planning and construction considerations.
What are the risks and benefits?
The risks and benefits of Mass Timber construction will vary depending on a variety of factors including the project’s intended use, location, and structural components. If the structure is all Mass Timber, there will be a different risk profile than if the structure is a hybrid of Mass Timber combined with steel and/or concrete, where tolerances between the materials must be carefully managed. If a project sits in a geography near a reputable Mass Timber manufacturer, that is obviously going to be a far different risk than a project that is getting their materials from across the country – or across the globe.
There is no “one size fits all” guidance for Mass Timber project risks but there are certain consistent themes. AXA XL’s North America Construction Property team’s recent whitepaper - Risk Considerations in Mass Timber Construction – delves into these themes.
Download the whitepaper here.
