The mass timber T3 Tower, in Minneapolis, is clad with weathering steel.
Blaine Brownell The mass timber T3 Tower, in Minneapolis, is clad with weathering steel.

Ancient Greek temples are considered exemplars of stone construction, yet they derive much of their formal language from the building material that predated stone masonry: wood. In the transubstantiation from wood to stone construction, Greek builders retained vestigial elements of the former material in their designs. For example, the Doric order’s triglyph and guttae motifs recall the sculpted ends of wooden beams and the pegs required for structural connections. These skeuomorphs—objects or features that the Oxford English Dictionary states imitate “the design of a similar artifact made from another material”—are familiar and convenient ways to retain the old within the new; yet they can also be considered irrelevant, nonfunctioning artifacts of the past.

The emergence of tall wood buildings raises the specter of architectural transubstantiation once more. Technologies like cross-laminated timber (CLT) and nail-laminated timber (NLT) have enabled high-rises to be realized with an environmental track record superior to reinforced concrete or steel. Several timber towers have been built recently in Europe, North America, and Australia, and many more are in progress. However, is engineered lumber simply supplanting structural concrete or steel, adopting the form of its ecologically inferior antecedents? That is, are today’s tall wood structures skeuomorphs of the modern frame?

The T3 office building in Minneapolis provides an appropriate litmus for this question. Designed by Michael Green Architecture (MGA) and architect-of-record DLR Group for real estate firm Hines, T3—short for “Timber, Technology, Transit”—is a seven-story, 220,000-square-foot structure scheduled to open later this month. It will be the largest mass timber building in the United States, according to MGA (although other tall-timber projects are on its heels).

Exploded diagrams of T3's structural floor and exterior wall systems
Courtesy Michael Green Architecture Exploded diagrams of T3's structural floor and exterior wall systems
Section rendering
Courtesy Michael Green Architecture Section rendering

MGA associate Candice Nichol says Hines wanted to use mass timber as a differentiator: “Hines understood that the market is looking for office spaces that people actually enjoy working in.” The simple, boxy design picks up visual cues from neighboring historic structures in Minneapolis’ North Loop district. From a distance, the structure looks like another speculative commercial building with a conventional column grid and repetitive floor plates. Yet how it performs both structurally and aesthetically reveals another story.

T3 uses spruce-pine-fir NLT panels combined with a spruce glulam post-and-beam frame, and a concrete topping slab. NLT was chosen because it was slightly more economical than other mass timber systems, at least for now. “The T3 structural framing system—columns on a 20- to 30-foot-grid, beams running one direction between columns, and panels spanning across the beams—is an efficient one,” says Lucas Epp, a structural engineer and 3D manager at Delta, British Columbia–based fabricator StructureCraft.

Leif Johnson, a senior associate at Seattle-based Magnusson Klemencic Associates, the project's structural engineer, notes that T3's structural bays are 20 feet by 25 feet, with the timber beams spanning 25 feet and the NLT panels spanning 20 feet. This one-way system enables building services to run parallel to the beams without clashes.

The system’s efficiency extends to the material sourcing and construction processes. Most of the project’s lumber came from trees in the Pacific Northwest region killed by the mountain pine beetle. (Though the mills did not record this exact quantity, they did certify all the wood under Sustainable Forestry Initiative guidelines.) Classified as a “Type IV–Heavy Timber” system by the Minnesota State Building Code, the sprinklered building is not required to have a specific fire rating. However, Epp anticipates the structure to achieve an equivalent rating of more than three hours based in part on the protective charring phenomenon of wood.

StructureCraft set up a prefabrication facility in Winnipeg, Manitoba, to supervise the manufacture of the NLT panels. Located within a six-hour drive from the jobsite, the facility also reduced transportation costs, ensured quality control, and enabled rapid construction: Construction crews erected 180,000 square feet of timber framing in 9.5 weeks, with 30,000 square feet of floor area installed per week.

Another benefit to timber is its lightness. According to Epp, T3’s structure weighs about one-fifth that of a comparable concrete building, subsequently reducing the foundation size, seismic loads, and embodied energy. R. Buckminster Fuller, who famously asked architects how much their buildings weigh, would approve.

T3 interior, circa October 2016
Blaine Brownell T3 interior, circa October 2016
T3 structural connection detail, circa October 2016
Blaine Brownell T3 structural connection detail, circa October 2016

The timber structure also lends itself to material and cost savings in interior finishes. Commercial buildings typically obscure their structure behind gypsum wallboard and acoustic ceiling tiles because not all occupants appreciate the look of exposed concrete or steel and its requisite fireproofing. Though its exterior is clad in weathering steel, its interior is simply the timber framework. “The entire timber structure of T3 will be left exposed and illuminated with a percentage of the interior lighting directed up to the ceiling,” Nichol says. At night, “the illuminated wood will glow from the exterior similar to a lantern.” A ground-level “social workspace” with wood furniture, booths, and a feature stair will also allow the public to experience the building.

“The final product has been very successful,” Nichol says. “The texture of exposed NLT is quite beautiful. The small imperfections in the lumber and slight variation in color of the mountain pine beetle wood only add to the warmth and character of the new space.”

With the exception of its conventional post-and-beam construction, T3’s functional and aesthetic qualities save it from becoming a skeuomorph. If anything, the opposite argument could be made: Mass timber has formed structures more ambitious than T3 long before the advent of concrete and steel. In fact, the nearby Butler Square building is a nine-story, 500,000-square-foot warehouse and office structure that is more than a century old. Rather than re-creating contemporary office buildings, T3 is paying homage to this timber heritage of its surrounding warehouse district neighbors. With the growing attention to construction’s environmental impact, more architectural projects will follow T3’s return to the original structural frame.

Editor's note: The article has been updated since first publication to clarify that Magnusson Klemencic Associates was the structural engineer for T3, and to specify the size of the structural bays.