“Tall Wood” Now Code Approved
It’s about to get a lot easier to build high with mass timber.
It all started when the American Wood Council (AWC), a trade group promoting the use of wood in construction, approached the International Code Council (ICC) with a request: study tall wood construction. In particular, AWC wanted some scientific rigor brought to the issue that’s often assumed to be wood’s Achilles’ heel: fire.
ICC formed the Ad Hoc Committee on Tall Wood Buildings in 2016, and the votes only recently came in. After years of study and testing, the codes will allow construction with mass timber materials such as cross-laminated timber (CLT) for buildings up to 270 feet tall. The changes will take effect with the 2021 version of the ICC building code.
This wasn’t the first time mass timber came to ICC’s attention, according to Stephen DiGiovanni, P.E., fire department protection engineer at the Clark County (Nevada) Department of Building and Fire Prevention. DiGiovanni serves as chair of the tall wood committee. “I would say there was a lack of scientific data and justification the first go-around,” DiGiovanni told BuildingGreen. “As part of the tall wood effort, we reviewed or helped … form additional test scenarios and test programs to answer some of those questions not answered the first time around.”
Laboratory tests carried out using ASTM standards have often shown that mass timber materials like CLT char instead of burning, contributing to their safety, but fears remained about how such materials might respond to a real-world fire—including whether adhesives might fail (technically termed delamination). So the ad hoc committee developed a plan. Working with AWC, the committee built and set fire to a full-scale two-story apartment mockup.
The results? “No collapses, no structural failures, and the fire was contained within compartments,” said DiGiovanni. Delamination was “minor” and deemed “not an issue,” he added.
That said, taller wood buildings (13 to 18 stories) will need to protect mass timber elements with gypsum board, and medium-height buildings (nine to 12 stories) require partial protection. Those up to nine stories can have exposed mass timber that’s designed for two hours of fire resistance.
More on tall wood construction
For more information:
International Code Council
Published February 4, 2019