When someone thinks “skyscraper,” they envision a multi-story building with gleaming windows and steel frames. But wood? That’s so 19th Century.
Except now, it’s not. Technological advancements in engineered wood—“mass timber”—are making it possible to construct high rises entirely or at least partially from wood.
Just ask the developers and builders of The Ascent in Milwaukee, who in 2018 had a modest goal of building a 19-story, multi-family luxury apartment building made of mass timber. By 2022, they were celebrating the opening of a 25-floor, 284-foot-high structure that was officially the world’s tallest wooden tower.
At that time, Tim Gokhman, CEO of project co-developer New Land Enterprises, said his firm didn’t set out to break records. “We just wanted to create the best experience within the built environment for our residents,” he noted. “Mass timber is faster, more precise, lighter, more beautiful, and supports our commitment to biophilic design.”
Ascent’s first six floors are allocated to retail space and a parking garage, while the remaining 19 floors, all of which are solid wood construction, are dedicated to 259 luxury apartment units. The entire project cost about $130 million, which is on par with traditional steel-concrete structures. Actual construction took 22 months—about 25 percent faster than expected with a non-wood alternative, according to research from the Council on Tall Buildings and Urban Habitat (CTBUH).
Mass timber is also quite a bit more environmentally friendly: Wood absorbs carbon dioxide (CO2) emissions, and Ascent sequesters more than 7,200 metric tons—the equivalent of taking 2,400 cars off the road for a year, or as much CO2 as would be emitted by heating 1,200 homes for one year, CTBUH notes.
New Land Enterprises and the other project participants—co-developer Wiechmann Enterprises, architecture firm Korb Architecture, structural engineer Thornton Tomasetti, timber sourcing provider Timberlab, and general contractors Catalyst Construction and C.D. Smith—had several ways to implement creation of The Ascent. There are four combinations of structural material (see the sidebar, “What’s the Difference?”), and five primary mass timber products:
Developers opted for a mass timber superstructure consisting of exposed glulam columns and beams supporting CLT floor panels. The CLT material came from sustainably managed rapid-growth European white spruce forests in Austria, which are cultivated specifically for forestation. The volume of timber used in construction regrows within 25 minutes throughout North American forests, according to Korb Architecture.
Meanwhile, glulam makes the building more fire resistant. Burn tests conducted by the USDA Forest Service’s Wood Innovations Grants Program and Forest Products Laboratory determined that oversized yet unprotected glulam columns do not lose structural integrity during a three-hour burn because there is only outer layer charring—the internal layers remain protected. Also, charring stops on its own after the heat source is discontinued. As a result, the columns easily qualified for Milwaukee’s mandatory three-hour fire resistance burn rating.
There are design benefits in Ascent that New Land Enterprises happily implemented. For example, the building includes efficient and space-saving hydronic radiant heating systems, which pump heated water from a boiler into tubing that is embedded into flooring. These systems don’t dry out the air, which means there is no ductwork required.
The cooling system consists of an energy-efficient variable refrigerant flow (VRF) system, as well as the latest water filtration techniques. The current stormwater management system slows the flow into the combined sewer, helping reduce the burden on the city’s infrastructure during a major storm event.
Meanwhile, the interior features exposed wood beams and ceilings in all living rooms and bedrooms, while sunlight filters through floor-to-ceiling windows, and ventilation draws in fresh air from Milwaukee’s lake breezes. All of these provide a more natural environment that, according to Gokhman, enhances people’s physical and emotional well-being. “It’s not just aesthetics,” Gokhman noted in a report by Development Magazine. “It’s the feeling you get from being in a building that has texture, warmth and natural elements. You feel better in it.”
Also feeling better with mass timber: Contractors, in terms of their bottom line. From an environmental standpoint, the production process for steel and concrete requires heating materials to very high temperatures, which generates most of their carbon emissions. The process is also fossil fuel dependent. Production of construction timber, in contrast, is at least partially powered by biomass or sawmill residue.
Because CLT panels are custom made away from the construction site and are transported readymade, there is up to 90 percent less traffic during construction. Approximately 75 percent fewer workers are needed, and it’s up to 40 percent faster to build with timber than with traditional materials. These benefits help offset the higher cost of CLT panels, which are typically 15 percent to 20 percent more, according to a report by KONSTRUKCE Media.
With regard to load bearing, timber walls are significantly thinner than concrete but still capable of handling the same weight. Ascent’s panels are 60 millimeters thick and are about five times lighter than traditional materials. This made it far easier to build the base of the tower, KONSTRUKCE Media notes. There’s also a lack of setting time versus that required with concrete construction, meaning that finishes can be added much sooner.
Korb Architecture founder Jason Korb calls the tower a proof of concept for developers who want to create innovative structures from timber. “We believe in the power of architecture as an engine for positive change,” said Korb to KONSTRUKCE Media. “Ascent could become an example for future high-rise wood buildings on a national scale in how it combines its environmental friendliness with modern and high-quality architecture.”
Mass timber high-rises have grown in popularity in the U.S. over the past decade. Projections show the number of such structures increasing from 2,000 in 2023 to more than 24,000 by 2034, according to McLean, Virginia-based tech industry policy coalition Chamber of Progress. That growth rate could be impacted for better or worse by rising lumber prices, regulatory hurdles, tariffs, interest rates, and a shaky economy.
Thus far, it hasn’t happened. Lumber prices have bounced up and down throughout 2025, with current figures as of November 1 down about 23 percent from the year’s high at the beginning of August, according to world economics forecaster Trading Economics. But overall, prices are up about 12 percent from October 2024, according to the National Association of Home Builders (NAHB).
Current prices may be down because some builders overprepared for proposed tariffs against Canada, which exports about 60 percent of its lumber to the U.S. “Everyone’s overstocked, so there’s no demand,” says wood market analyst Russ Taylor. “It’s going to take months before all of this unwinds.”
But housing starts have increased, which, combined with lowering interest rates, could boost lumber prices again, Taylor adds.
The mass timber market, meanwhile, is expected to grow by about 4.5 percent from 2025 to 2030, reaching $1.3 billion, according to market research group Research and Markets. The market growth, it notes, “is driven by a combination of climate policy alignment, urban housing needs, supply chain modernization, and investor interest in green building innovation.”
Not all mass timber projects are the same. There are four types of wood-based structures that are considered to be “mass timber.”
• All-timber structures. To qualify as an “all-timber” structure, both the main vertical and lateral structural elements must be constructed from timber. An “all timber” structure may include the use of localized non-timber connections between timber elements. A building of timber construction with a floor system of concrete planks, or concrete slab on top of timber beams, is still considered a “timber” structure, as the concrete elements are not acting as the primary structure.
• Concrete-timber hybrid structures. In these buildings, a significant element of the vertical or lateral load-bearing system is made of concrete, often presented as a concrete core supporting a timber frame. Other commonly seen examples include buildings that use lateral spanning elements, such as beams, and vertical load bearing columns made of concrete, with timber serving as the main floor decking system. Several of the factory-prefabricated systems on the market integrate concrete frames with timber inlay panels for walls or flooring, or timber-framed modules with pre-poured concrete flooring.
• Steel-timber hybrid structures. In these projects, a significant element of the vertical or lateral load-bearing system is made of steel. Most typically, this will be a lateral force-resisting system such as steel-framed cores, buckling-restrained braces, perimeter-frame or exoskeleton steel bracing systems and a gravity system composed of columns and beams that interact with a timber floor or wall system. Generally, this structural classification is meant to reflect a substantial use of steel, beyond the fasteners and connectors used in typical mass timber and wood-frame construction.
• Concrete-steel-timber hybrid structures. These buildings use a combination of all three materials to carry primary loads. The most typical combination would be a concrete core working in tandem with steel beams and columns, with timber flooring and partition walls, but many variations exist.
Source: Council on Tall Buildings and Urban Habitat (CTBUH)
The world’s five-largest mass timber buildings have their own identities within the wood tower design spectrum:
1. The Ascent, Milwaukee, Wisconsin: As noted, this concrete-timber hybrid structure is the tallest all-residential tower—for now.
2. Mjøstårnet, Brumunddal, Norway: Although it was knocked off its No. 1 perch by The Ascent in 2022, Mjøstårnet—all 280 feet and 18 stories of it—is still the world’s tallest all-wood timber structure.
3. HoHo Wein, Vienna, Austria: At 24 stories and 275 feet, this is the largest mixed-use (hotel and office space) concrete-timber hybrid structure.
4. HAUT, Amsterdam, Netherlands: Twenty-two stories, 239 feet and 55 apartments—good for the title of tallest all-residential concrete-timber hybrid in the Netherlands.
5. Sara Kulturhus, Skellefteå, Sweden: The world’s current tallest (238 feet, 19 floors), mixed-use, steel-timber hybrid building.