The Type IV-B code path has existed since the 2021 IBC. No U.S. office developer has taken it to the limit, largely because nobody wanted to be first to argue fully exposed timber ceilings past a fire marshal.
Mithun and London-based Waugh Thistleton Architects revealed the design of Bevel on August 11: a 12-story, roughly 200,000 rentable square foot mass timber office tower at 106th Avenue NE and NE 9th Place in downtown Bellevue, Washington. Skanska is both developer and builder. At 180 feet, WoodWorks says it would be the tallest mass timber commercial office building in the country.
The height isn’t the precedent. The ceilings are.
Maxing out Type IV-B height and story limits makes a good headline. The approval that other design teams will actually copy is the one for 100 percent exposed timber, with columns, beams and ceilings left visible across the office floors and the ground-floor public areas.
Exposed mass timber is the whole point of building in wood and it’s also the hardest thing to get approved, because char-rate calculations and encapsulation requirements are where most tall-timber schemes quietly lose their wood. Getting a jurisdiction to sign off on full exposure at 12 stories creates a reference other teams can cite.
“Bevel is notable for what will become the tallest mass timber office building in the U.S., but it’s also expanding the idea of what’s possible with these projects,” said Jennifer Cover, president and CEO of WoodWorks. “Of the 22 tall timber buildings under construction or built, only three are commercial. A tremendous amount of work also went into gaining approval for the 100% exposed timber ceilings.”
A hybrid structure, because Bellevue is a seismic zone
Above grade the structure is mass timber. The core and lateral system are steel, and the below-grade parking is concrete. That combination reflects where the Puget Sound seismic demand actually lands, and it’s a reminder that “mass timber building” in high-seismic territory almost always means a hybrid.
Mithun makes a design argument for the timber that has nothing to do with carbon: a concrete center-core scheme on this tight site produced narrow, awkward floor plates, while the timber scheme allowed a side core and better usable area. The firm also says mass timber hit cost parity with concrete here, driven by efficient timber design and a shorter schedule. That’s an internal comparative study with no published numbers and no third-party validation. Report it as the architect’s claim.
Targets are LEED v4 Platinum, Fitwel 2-Star and Salmon-Safe, fully electrified, with stormwater capture and reuse. No embodied-carbon figure has been released.
It isn’t financed yet
Bevel is still in design and entitlement with the City of Bellevue. There’s no construction start, no completion date, no published project cost and no anchor tenant. Skanska conditions the build on customer demand, market opportunities and its own long-term investment strategy, which is developer language for not yet.
The site sits next to The Eight, Skanska’s completed LEED Platinum Bellevue tower, now about 90 percent leased. That’s the real underwriting case.
Exposed structural wood is also finding its way into much smaller institutional work, including the wood-clad pavilions planned for the Brandywine Museum of Art campus expansion. If Mithun’s cost-parity claim survives real subcontractor bids, the last defensible objection to tall timber in commercial work stops being economics and starts being habit.