NFPA Journal

BY ANGELO VERZONI 

The recent full-scale fire test of a mass timber building—the largest of its kind ever conducted, according to an industry group—demonstrated how such structures can remain intact after a large fire destroys everything inside them. 

That was the takeaway according to the Canadian Wood Council (CWC), which hosted the burning of a two-story, 3,700-square-foot mock office building in June. The test was conducted at the Canadian Explosives Research Lab in Ottawa.

“Mass timber performed as expected: the mass timber structure withstood the full burnout once the furnishings of the building were consumed, then the fire quickly died down and burned out,” the CWC said in a statement. It was the fifth in a series of mass timber fire tests hosted by the CWC this summer.



1: Combustible materials begin burning inside the mass timber structure. 2: The structure is fully engulfed. 3: After about an hour, the fire has died out on its own, leaving the structure intact and standing.  Photos courtesy of Canadian Wood Council

Testing like this, proponents of mass timber construction say, is critical if the construction method is going to gain widespread global popularity, as many have envisioned. Already, there are thousands of mass timber buildings either completed or being planned for construction around the world, including more than 135 that are eight stories or taller. But critics are concerned that the buildings are less fire-safe than their steel, concrete, or brick counterparts. 

Mass timber is a term used to describe a construction method that involves joining pieces of soft wood together with nails or glue to form larger, stronger structural pieces. While the technology is regarded by many builders as a more environmentally friendly and sometimes less-expensive alternative to steel or concrete, it has also sparked fears over fire safety, especially when mass timber is used to construct high-rises—buildings that are sometimes referred to as tall wood buildings. 

In 2020, changes to the 2021 editions of NFPA 5000®, Building Construction and Safety Code®, and NFPA 101®, Life Safety Code®, allowed for mass timber buildings to be constructed as tall as 270 feet, provided they meet certain fire safety requirements such as having exit enclosures and elevator shafts made from noncombustible or limited-combustible materials. Previous requirements limited mass timber to 85 feet. Currently, the world’s tallest mass timber building, located in Norway, stands at 280 feet.

The new code allowances were informed in part by a two-phase study conducted from 2013 to 2018. The research, which was supported by the Fire Protection Research Foundation (FPRF), found that the fire performance of mass timber buildings is complex and influenced by a number of factors. This can include the types of adhesives used to form the large wood beams, ventilation inside the structure, and how much noncombustible or limited-combustible materials, such as gypsum wallboard, are used to shield the beams from heat and flames arising from interior fires. Still, the tests performed during the five-year period showed, just as the recent CWC testing showed, that mass timber buildings won’t burn to the ground nearly as easily as lightweight wood-frame structures that use smaller, untreated beams. 

To learn more about the FPRF research on tall wood buildings, including a new study the foundation is working on, visit nfpa.org/tallwood.

ANGELO VERZONI is a staff writer for NFPA Journal. Follow him on Twitter @angelo_verzoni. Top photograph: CWC