On the northern edge of downtown Milwaukee, one high rise is not like the others.
A typical tall apartment building is held up by steel and cement — the Ascent is made of wood.
But it’s not just any old lumber. The top 19 floors of the 25-story building are made with cross-laminated timber or CLT, an engineered wood created by layering and gluing lumber in a crossing pattern to form massive, strong beams.
As Midwestern builders look for ways to construct more sustainably, some are thinking about wood in a new way. They’re turning to mass timber to create structures that will have a positive effect on the environment, while also ensuring longevity and beauty.
A world record
The Ascent is currently the world’s tallest timber concrete hybrid building. Inside, the exposed mass timber gives the luxury building a unique look.
“Oftentimes when people come into this building, the first thing they do is they put their hands on a column,” said Jason Korb, the architect behind the project and a principal at Korb and Associates Architects. “People want to be around natural materials.”
In a model three-bedroom unit that rents for almost $7,000 a month, the ceiling is made of warm exposed timber that connects to thick wooden support beams, framing a stunning view of Lake Michigan. In hallways, wallpaper has a tree-themed pattern, referencing the wood skeleton.
At first, Korb said the Ascent’s developers thought of cross-laminated timber as a way to set their project apart from competition aesthetically.
“But the more you dive into it, the more you learn about its other benefits,” Korb said. “The largest one is the level of carbon sequestration in the timber.”
It’s estimated this building will offset 72 metric tons of carbon dioxide, Korb said. That’s the amount of emissions produced to heat and cool about 1,100 homes in Milwaukee for a year.
Environmental benefits like those are sparking a growing interest in mass timber.
Hard to clean up
The earth is getting warmer as humans burn fossil fuels, emitting gases like methane and carbon dioxide into the environment. Those are known as greenhouse gases, because they trap heat, acting like a blanket wrapped around the earth. As greenhouse gases reach record highs in the atmosphere, scientists are also recording record high temperatures globally.
Producing traditional building materials such as steel and cement takes a lot of energy, which in turn leads to pollution. Together the two are responsible for almost 15% of planet warming greenhouse gas emissions worldwide.
Cleaning up those materials is one of the most difficult puzzles in the fight against climate change, said John E. Fernández, a professor of architecture at MIT and director of the MIT Environmental Solutions Initiative.
“There still aren't really great solutions to reducing emissions,” Fernández said. “So avoiding consumption, and therefore avoiding the production of steel and concrete, by way of the substitute of wood, can be a benefit.”
The wood in the cross-laminated timber is also literally removing carbon from the atmosphere.
“When you look at a tree, the fact is that about half of the dry weight of that tree is carbon,” Fernández said.
Cutting down that tree to turn it into cross-laminated timber stores carbon in a building for a long time.
Of course, Fernandez said it’s important that the wood is sustainably harvested from a forest that is healthy and managed well. And there’s another caveat — trees take a long time to suck up carbon, Fernández said.
“Growing a tree and capturing carbon takes time, takes decades,” he said. “That's not a solution for the climate crisis that we're facing now.”
But there’s another surprising benefit to building with wood; it's good for the environment to build something beautiful.
“The most sustainable thing a building can do is just last for a very long time, not be demolished and replaced,” Fernández said. “And so the more we value and appreciate the aesthetics, the interior feeling of a building, the pleasure of being in a space ... that just lends a lot of power to the idea that we should preserve this building.”
A growing market
Despite the potential to fight climate change, cross-laminated timber is still a relatively rare building material in the U.S.
“It's, you know, really in its infancy,” said Bill Parsons, the chief operating officer of WoodWorks Wood Products Council, which is a nonprofit funded by the forestry industry to encourage more use of wood.
Cross-laminated timber first took off in Europe in the ‘90s, Parsons said. It’s taken a while to get to the U.S., but now, the industry is growing quickly, by 20 to 30% in recent years.
“We really see this continuing to be this rapid growth, through even all of the economic conditions and the pandemic,” Parsons said.
For some architects, other forms of mass timber eventually lead to interest in cross-laminated timber.
A swirling wood structure at the St. Louis Science Center is made of huge arched beams, creating a swooping ceiling that looks like the hull of a wooden boat. This is the GROW Pavilion, part of an exhibit designed to teach kids about agriculture.
This form of mass timber is called glue-lamination or glulam; like cross-laminated timber, the wood is glued together, but without the crossing pattern in CLT.
Architect Chrissy Rogers collaborated with the late architect Gyo Obata to design this structure. She says glulam was the best way to achieve the curved, sculptural profile, but it was also appealing for its environmental benefits.
“We are very focused on trying to decarbonize our projects and get to a carbon neutral approach to our work,” Rogers said. “So bringing wood into those projects is really a substantial way to do that at the beginning.”
Now, Rogers is working on a new project in mid-Missouri that features cross-laminated timber, and she is trying to find other ways to incorporate wood.
“We are hopeful that it gains some momentum here,” Rogers said. “So far, the Midwest is a little bit slower to adopt more frequent use of timber, but we are actively trying to engage on using it in projects pretty regularly.”
Projects on the horizon
St. Louis used to have lots of multi-story buildings built with massive timber. But this wasn’t engineered wood; in the late 1800s and early 1900s, many of St. Louis’ iconic brick buildings were held up by huge wooden beams, each cut from just one gigantic, ancient tree.
In St. Louis’ Downtown West neighborhood, AHM Group, a development company, owns an 1890s-era building. AHM Group Principal Kyle Howerton says this neighborhood is changing quickly thanks to St. Louis’s new soccer stadium, just two blocks away.
“Until the MLS stadium construction started, this was really the donut hole of development,” Howerton said. “It was a donut hole of development, because for the cause of urban renewal, a lot of historic structures were demolished in the middle of the 20th century.”
Luckily, this brick beauty survived. Howerton and another AHM Group principal, Rob Maltby, enter a room with exposed brick walls and hardwood floors. A thick antique beam with visible swirling tree rings holds up the ceiling.
“Now cross-laminated timber, or mass timber, is effectively doing the same thing that old-growth forests do, but with newer, more sustainable harvested wood that is younger,” Maltby said.
Next door, a gravel lot doesn’t look like much right now, but next year AHM Group plans to break ground on a mass timber high rise that’s a bit taller than the record-holder in Milwaukee and also designed by Korb.
Just as professional soccer brought new life to this part of the city, Howerton hopes the new mass timber high rise will spark inspiration.
“I hope that this is a catalyst for more structures being built using the same technologies,” Howerton said. “It feels really nice, and it could help St. Louis kind of be placed on the sustainability map.”
This story was produced in partnership with Harvest Public Media, a collaboration of public media newsrooms in the Midwest. It reports on food systems, agriculture and rural issues.
