How 'Plyscrapers' Are Replacing Concrete and Decarbonizing City Skylines

For over a century, the recipe for a skyscraper has remained stubbornly fixed: pour the concrete, forge the steel, and build toward the clouds. But across the globe, a quiet revolution is taking root in urban architecture. Cities are beginning to grow out of wood. In Milwaukee, Wisconsin, construction is underway on The Edison, a 31-story high-rise that will become the tallest timber building in the world when it tops out in 2026. It is part of a booming architectural movement known as mass timber, which promises to replace heavy, carbon-intensive materials with engineered wood.[3][6]

The stakes for this transition are monumental. The global construction industry is under immense pressure to decarbonize, and for good reason. The production of cement alone accounts for an estimated 8% of all global carbon dioxide emissions. When combined with the energy required to forge structural steel, the traditional building sector is one of the heaviest polluters on the planet. Concrete construction at its current scale is widely considered unsustainable, prompting architects and developers to search for viable alternatives that do not compromise structural integrity.

Enter mass timber. This is not the traditional "stick-frame" lumber used to build suburban homes. Mass timber refers to a category of advanced, engineered wood products created by binding smaller pieces of wood together under immense pressure to form massive, solid panels and beams. By industrially processing the wood—removing knots and aligning the fibers—manufacturers can create structural components that rival the strength of steel and concrete.[1][4]

The backbone of this movement is a product called Cross-Laminated Timber, or CLT. To manufacture CLT, mills take standard planks of solid sawn lumber and stack them in alternating layers, typically three, five, or seven plies thick. Crucially, each layer is oriented at a 90-degree right angle to the one below it. Once bonded with high-strength structural adhesives and pressed together, this cross-hatching technique harnesses the wood's tensile strength in two directions. The result is a rigid, highly stable panel that can span up to 60 feet and serve as load-bearing walls, floors, and roofs.[1][2]

While CLT handles the flat surfaces, another mass timber product carries the heavy vertical loads: Glue-Laminated Timber, or Glulam. Unlike CLT, the wood grains in Glulam are all aligned parallel to the longitudinal axis of the piece. This unidirectional alignment makes Glulam exceptionally strong in one direction, making it the ideal engineered material for massive structural columns and long-spanning beams. Together, CLT and Glulam form a complete structural system capable of supporting high-rise towers.[1][4][6]

The most immediate question the public asks about wooden skyscrapers is inevitable: What happens in a fire? It is a deeply ingrained instinct to view wood as fuel, making fire safety the primary psychological hurdle for mass timber adoption. However, engineered mass timber behaves entirely differently in a fire than the thin 2x4s used in residential framing. Its defense mechanism relies on a natural process known as charring.[5][6]

When a massive, solid block of timber is exposed to intense heat, the outermost layer burns and turns to char. This charred layer is porous and highly insulating, acting as a protective shield that prevents oxygen and heat from penetrating deeper into the wood. Because mass timber lacks the air pockets found in traditional stick-frame construction, the fire is starved of the oxygen it needs to spread rapidly. The char forms at a highly predictable rate of about 1.5 inches per hour, allowing structural engineers to calculate exactly how thick a beam needs to be to survive a prolonged fire.[5][6]

Rigorous physical testing has repeatedly validated this self-protecting mechanism. In tests conducted at the federal Alcohol, Tobacco, Firearms and Explosives (ATF) Fire Research Laboratory, a 5-ply CLT wall panel was subjected to temperatures exceeding 1,800 degrees Fahrenheit. The panel maintained its structural integrity for over three hours—far exceeding the standard two-hour fire rating required by most high-rise building codes.[5]

In many ways, mass timber can actually outperform traditional materials in a catastrophic fire. While steel is non-combustible, it is highly thermally conductive. Under extreme heat, steel beams can rapidly lose their strength, warping and buckling, which can lead to sudden structural collapse. Concrete, meanwhile, can crack and spall as the moisture trapped inside it expands rapidly under high temperatures. Mass timber, protected by its insulating char layer, maintains its structural load-bearing capacity much longer, giving occupants crucial time to evacuate safely.[5][6]

Beyond safety and sustainability, mass timber is transforming the actual process of construction. Traditional concrete buildings require a chaotic, noisy, and labor-intensive process of pouring and curing on-site. Mass timber, by contrast, is entirely prefabricated. Every panel, beam, and column is custom-manufactured in a factory, with openings for doors, windows, and plumbing pre-cut with millimeter precision using digital modeling.[1][4]

When the timber components arrive at the construction site, they are assembled much like a giant piece of flat-pack furniture. This prefabrication drastically reduces the number of truck deliveries required and minimizes on-site waste. Because the pieces simply need to be hoisted into place and bolted together, mass timber buildings can be constructed up to 50% faster than their concrete counterparts, requiring a fraction of the on-site labor force.[4]

The environmental benefits of this system extend far beyond simply avoiding the use of cement. Trees naturally absorb carbon dioxide from the atmosphere as they grow. When those trees are harvested and turned into mass timber, that carbon is locked away within the building's structure for decades, or even centuries. By replacing steel and concrete with wood, a mass timber building achieves a double climate benefit: it avoids the massive emissions of traditional construction while actively sequestering carbon within its walls.[4][6]

However, the environmental promise of mass timber hinges entirely on sustainable forestry. If the demand for CLT leads to the clear-cutting of old-growth forests, the ecological damage would outweigh the carbon benefits. The industry relies on certified, sustainably managed forests—often utilizing fast-growing softwood species like spruce, pine, and fir—where new trees are continuously planted to replace those harvested. Forestry experts argue that a robust market for mass timber actually incentivizes better forest management and increased planting, turning commercial forests into efficient carbon-capture engines.[1][2]

The global race to build taller with timber is accelerating. Milwaukee currently holds the record with its 25-story Ascent building, completed in 2022, but the upcoming 31-story Edison tower will soon surpass it. In Canada, the University of Toronto is completing a 14-story Academic Wood Tower, while Sweden is developing 'Stockholm Wood City,' a massive urban district built entirely of timber. In Japan, ambitious conceptual projects like the W350 tower aim to push timber construction to 70 stories by the 2040s.[3][6]

As building codes adapt to recognize the safety and strength of engineered wood, mass timber is poised to move from a niche architectural marvel to a mainstream construction standard. It represents a rare technological leap that looks backward for its inspiration, taking humanity's oldest building material and re-engineering it to solve the defining architectural challenge of the 21st century.[5][6]