Editor's note: Call to Earth is a CNN editorial series dedicated to reporting on the environmental challenges facing our planet and their solutions. The Rolex Perpetual Planet Initiative has partnered with CNN to promote awareness, education and inspire positive action on key sustainability issues.
CNN —
The US city of Milwaukee is already home to the world's tallest wooden tower, but an even taller wooden skyscraper designed by Vancouver-based architecture firm Michael Green Architects (MGA) may be joining the Milwaukee skyline.
The company recently unveiled plans for the development, which includes a 55-story tower made primarily from mass timber (multi-layered panels of thick, compressed solid wood) that, if built, would become the tallest building in Wisconsin, beating the current world title holder, Kolb & Associates Architects' 25-story Ascent Tower.
Timber building specialists MGA hope the project will set “a new global standard for mass timber construction”.
The project is part of the redevelopment of the Marcus Performing Arts Center, which opened in 1969 and received an Architectural Design Excellence Award from the American Institute of Architects in 1970. Led by Neutral, which describes itself as a “revitalization development firm,” the redesign will transform what is currently the center's concrete parking lot into space with housing, offices, restaurants, cafes, a grocery store and a public plaza. Construction will cost an estimated $700 million, according to MGA. The plans are currently going through the city approval process and are expected to evolve along the way.
The use of mass timber has been steadily increasing around the world due to changing building codes and attitudes toward wood, but while a number of wooden high-rises have been proposed in recent years, they still don't come close to matching the heights of buildings made from concrete or steel.MGA says its tower design will be about 600 feet (182 meters) tall, more than double the height of the 284-foot (87-meter) tall Ascent Tower.
“The height contest is important,” says Michael Green, an architect and founder of MGA, “not for show, but to show the public what's possible.”
He argued that wooden high-rises haven't yet become mainstream because climate change hasn't been at the forefront of the discussion. “There's been no need to challenge the status quo of steel and concrete,” he said. “But these materials are very bad for the climate, so we needed to find another way to build towers and big buildings.”
Currently, the building and construction sector accounts for 37% of global emissions, much of which comes from the production and use of carbon-intensive materials like concrete and steel. Trees, on the other hand, absorb carbon throughout their lives. When these trees are processed into bulk timber and used in construction, that carbon is “sequestered,” or sequestered, for the life of the building. “When you build with that, you're actually building with a carbon sink,” Green argued.
But they acknowledge that sourcing enough sustainable timber on the scale needed to build a city may be difficult – indeed, some studies have warned that increasing demand for large amounts of timber could increase pressure on land use.
To achieve carbon reduction benefits, trees need to be grown for long periods of time to sequester carbon and then replanted when they are harvested, and Green said MGA uses wood from responsibly managed forests in North America.
In the long term, he thinks builders will need to think beyond wood to address supply issues, adding that MGA is currently working on developing other plant-based building materials. But he argues that if you want to reduce your use of concrete and steel, mass timber is “the best option right now.”
Other obstacles to the use of mass timber are both cost and strict building codes. But in recent years, this has changed, and mass timber can now compete cost-wise with concrete and steel in many areas, Green explains. “There are more manufacturers than ever before. There's a big, competitive market now, and it's still growing,” Green says.
Building codes are also evolving, with some European countries mandating the use of wood construction as part of their climate goals, and in the United States, the International Building Code updated its mass timber policy in 2021 to allow mass timber buildings six stories and above.
Green said Milwaukee has been particularly forward-thinking, encouraging development in the city center while also being open to experimenting with new materials. The proposed tower will still have a concrete foundation and steel components for the elevator core, but Green estimates that about 90 percent of the building materials will be wood.
“It's America's second-largest city that's breaking new ground with innovations that will help manage climate change,” he said.
He hopes the Milwaukee Tower will spur innovation in climate-friendly architecture and broaden people's imaginations about building with wood.
“We need a breakthrough, and now is the breakthrough,” Green said.
