The Edison is officially going up! The 31-story, hybrid mass timber building in Milwaukee being developed by Neutral (formerly the Neutral Project) began construction earlier this month. Appropriately, the building site, which is situated in the city’s Deer District, on the eastern bank of the Milwaukee River, was once a lumberyard. When completed, the Edison will become the world’s tallest mass timber residential building. (The future tallest in this construction category will likely belong to Atlassian Central, a 39-story commercial tower currently going up in Sydney.)

In the months that followed GBA’s most recent coverage of this development, I connected with Daniel Glaessl, partner and chief product officer at Neutral. I asked him, in light of the fact that Milwaukee is already home to the world’s tallest mass timber building (the 25-story, 284.1-ft.-tall Ascent MKE), what the “secret sauce” is in Milwaukee, seeing this is now modus operandi within city limits.

“Milwaukee is in a very special economic condition,” Glaessl said. “The city is growing, and it has a high absorption rate for residential product. The construction costs are comparatively low. It is actually one of the few economically feasible markets right now in the U.S.”

Glaessl adds that the city is clearly “open to new construction techniques,” evidenced by the recently completed Ascent, and has an extensive approval process for tall mass timber. To a developer and real estate investment company like Neutral, whose stated mission is to, in part, leverage “sustainable construction materials to build carbon-neutral structures,” this is an invitation to go above and beyond. In that vein, the Edison is designed to meet the standards of Phius 2021 Core certification as well as Living Building Challenge Core certification, under version 4.0. “We’re not even using the current [2015 IECC] code, so you have more flexibility with your design. The code doesn’t even state exposure requirements.” Glaessl also confirms that his company has completed successful red flag reviews with both Phius and Living Future.

A new paradigm in sustainable high rise

When I first visited this topic in late 2023, I admit I may have taken some cheap shots. After all, the idea of designing mass timber high-rises as an exercise in engineering prowess and showmanship, all while pumping one’s fists in the name of “long-term carbon storage,” feels a bit like greenwashing 2.0. It’s sleight of hand, drawing our gaze toward reductions in operational carbon and away from the embodied carbon tied to materials and shipping. Besides, building with mass timber at any scale doesn’t automatically make your building sustainable, high performance, and low impact.

However, just by the Edison pursuing Phius Core, which rarely applies to tall buildings, and Living Building Challenge Core, which is quite rare and very difficult to achieve unto itself, there is evidently far more to this project than meets the eye.

Neutral’s first foray into mass timber is taking shape in its home base of Madison, Wisconsin. The Michael Green Architecture-designed Bakers Place, now nearing completion, is a 14-story, 206-unit multifamily building that, by Glaessl’s estimates, will achieve a 35% reduction in upfront biogenic carbon. The Edison is taking a more aggressive stance, he says, owing to its targeted certifications as well as the project team’s intent to achieve a 55% reduction in embodied emissions.

The project team includes architecture by Hartshorne Plunkard (HPA), Thornton Tomasetti (structural and façade), dbHMS (MEP and Passive House consultant), C. D. Smith Construction (general contractor), and several others. Glaessl calls the Edison the product of an “integrated project delivery model.” In other words, something of this scale, size, and complexity demands an interdisciplinary team of designers, engineers, energy modelers, and more, all of whom know how to be efficient and flexible in the same meeting.

According to Paul Alessandro, a partner with HPA, “The Edison only works if it’s successful from a commercial standpoint. It can meet all the quantitative measurements and still not be successful. That’s why this team has assembled a coordinated strategy to embrace technology and innovative thinking to achieve our various goals … It’s necessary to look beyond the numbers and to find opportunities to make good architecture that both acknowledges and exceeds the prescriptive paths.”

That’s one big passive house

The three pillars of the Phius standards include the building’s environment (limits on heating and cooling loads, peak and annual), occupant experience (air-tightness and other prescriptive quality assurances), and efficiency (limits on overall source energy use). Like the finer points in any green building certification, all of that reads great, but the implications of deploying each pillar within a 31-story, 378-unit, 385,109-sq.-ft. residential building are anything but straightforward.

Scott Farbman, former innovation lead at dbHMS, admits that WUFI, Phius’s standard energy-modeling software, is not accustomed to handling passive design projects of this scale and size. When the geometries change during design, which is common for large multifamily buildings, the impacts trickle down to other aspects of the building and its desired performance. He lists considerations like occupant density, heating and cooling loads, plug loads, solar gains, envelope-to-floor-area ratio, and more.

“The targets on a Phius-certified single-family home don’t quite transfer to the scale of this building,” Farbman says, while noting that the internal heat loads for a high rise come to 1.8 BTU/hr/sq. ft., which is more than double the amount for a single family. “Getting to similar occupant densities depends on how many dwelling units per floor, and there are a lot of studios, and two- and three-bedrooms. That changes the parameters and impacts your heat loads, which is what Phius is trying to manage at the end of the day.”

For principal cooling and heating, the building will utilize water from the adjacent river and district steam from local power generation, respectively. HPA’s Alessandro further points out that loads are being managed with high-performance glazing, and insulated spandrel and cladding elements, resulting in an exceptionally airtight building.

Mass timber exposed

Mass timber buildings often benefit from being their own billboards, proudly placing their principal constituent material on display, outward facing, in all its biophilic glory. But that proposition becomes a bit tricky when you’re building toward the heavens. Alejandro Fernandez, a Chicago-based structural engineer with Thornton Tomasetti, notes “there is a bit of nakedness” to the Edison in that “it exposes [much of] its mass timber structure.”

“When designing this tower, we looked to the past to see what’s been done and came up with a pretty innovative system,” Fernandez says. The traditional makeup of mass timber towers, like those found in the Ascent, feature a series of timber columns, beams, and slab placed atop a large concrete base. “The system we’ve developed creates a timber base that falls down at the column lines, allowing for the creation of some concrete beams.” This results in more “efficient connections,” Fernandez said. “We can reduce the amount of material in the structure but also on the facades and the partitions. This system allows us to integrate the mass timber in a way that is cost efficient.”

Granted, the timber that is technically “exposed” on the Edison is mostly limited to its interiors, save for the units’ bathroom and kitchens. But making timber an integral building component of the structure’s base, and thus creating opportunities to showcase it via glazing and other openings on the lower floors, represents a significant game-changer for the industry.

By all accounts, Neutral appears to have done its homework and is not waging some “race to the sky” for its own sake. With construction now underway, the project is slated for completion sometime in 2027. Should the Edison meet or exceed its stated performance and emissions reduction targets, the growing cast of mass timber towers around the world won’t just have a new supertall for the record books, but a singular standard bearer for high-performance design. Still, records are meant to be broken.

Last fall, Neutral was selected by the city of Milwaukee to redevelop the parking garage for the Marcus Performing Arts Center, with Michael Green Architecture attached to the project. There is already talk that this development will produce “the tallest mass timber building in the world.”

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Justin R. Wolf is a Maine-based writer who covers green building trends and energy policy. He is the author of Healing Ground, Living Values: Stanley Center for Peace and Security, published by Ecotone. Drawing courtesy of Neutral.