As Washington looks to bring cross-laminated timber (CLT) into mainstream construction use, the International Code Council (ICC) has announced code change proposals that would represent another large step in that direction.
In late November the Washington State Building Code Council (ICC)unanimously approved rules for using CLT for buildings up to 18 stories. Now, the ICC is proposing 14 CLT or “mass timber” code change proposals that would create three new types of construction similar to that approved by the Washington code council. Under the proposed rules, CLT will be allowed for building up to 18 stories, but sets three different design requirements (18, 12 and nine stories, respectively). If approved, they would be incorporated into the 2021 International Building Code.
The announcement came two years after ICC created the Ad Hoc Committee on Tall Wood Buildings; a group thatconsists of building officials, fire officials, architects, fire protection engineers and industry experts. Its work included fire testing of various CLT buildings. A 2018 fire testing of rooms with exposed CLT by the National Research Council Canada found that allowing some exposed mass timber in their national building code would “be unlikely to increase the fire risks significantly to life and property.”
“Mass timber has been capturing the imagination of architects and developers, and the ICC result means they can now turn sketches into reality,” American Wood Council (AWC) President CEO Robert Glowinski said. “ICC’s rigorous study, testing and voting process now recognizes a strong, low-carbon alternative to traditional tall building materials used by the building and construction industry,” he said.
The proposed changes are an acknowledgement of new technology that allows for small-diameter trees to be used in construction. Traditionally, these stands are harvested mainly as part of pre-commercial thinning projects and are sold, if at all, for pulp or biomass products that offer little commercial value. That has made it problematic for the various state and federal agencies that want to remove these trees in Washington’s forestland as they contribute to over-density and are much more susceptible to wildfire than old growth trees.
In Washington, one of the leading advocates for CLT has been Forterra, one of the state’s largest conservation organizations. According to a Dec. 6 blog post, “the alteration of these building codes will support of a new generation of engineered wooden building materials with exciting properties of strength, durability and beauty. With mass timber, architects and builders acquire a new material to create with and rural areas gain the prospect of new high-skilled, high-paid jobs.”
“As mass timber becomes more widely utilized, it has great potential to support employment in rural areas, improve forest health on public lands in need of restoration, and enable new and affordable approaches to building for fast-growing urban populations,” Forterra President and CEO Michelle Connor said.
The code changes are expected to be approved in October 2019, with the 2021 IBC released in 2020. Final approval of 2019 proposals is expected to occur in late October. The 2021 IBC is expected to be released in late 2020.