The skylines of major cities tell the story of modern civilization. For over a century, those stories have been written in steel and glass, with concrete providing the backbone for increasingly tall structures. But a quiet revolution is underway. Architects and builders are returning to one of humanity’s oldest building materials and reimagining it for the age of high-rise construction. These timber towers, often called plyscrapers, represent a fundamental shift in how we think about tall buildings. For a closer look at how water systems integrate with these sustainable structures, read about water recycling in the home and the lessons drawn from modern building innovations.
The Rise of the Plyscraper
The concept of building tall with wood defies intuition for many. Steel and concrete have dominated high-rise construction since the late 19th century, yet recent advances in engineered wood products have made timber a viable alternative for structures well beyond ten stories. The term plyscraper captures the imagination, but the technology behind these buildings is anything but fanciful. Host Kevin O’Connor explored this topic in the Plyscrapers episode of the Clearstory podcast, speaking with architect Michael Green and Lynn Osmond of the Chicago Architecture Center about the potential of tall wood buildings.
What Makes a Plyscraper Possible
The key enabling technology is mass timber, a category of engineered wood products that deliver strength and dimensional stability far beyond conventional lumber. Mass timber products are manufactured by layering and laminating smaller pieces of wood into large structural elements. The result is a material that can rival steel and concrete in load-bearing capacity while weighing significantly less.
Cross-Laminated Timber
Cross-laminated timber (CLT) is arguably the most important mass timber product. It consists of layers of dimensional lumber stacked perpendicular to one another and bonded with structural adhesives under high pressure. This crosswise lamination gives CLT remarkable strength in both directions, making it suitable for floors, walls, and roofs. Panels can be manufactured up to 60 feet long and shipped to job sites for rapid assembly.
Glued Laminated Timber
Glued laminated timber (glulam) consists of individual lumber fingers bonded with moisture-resistant adhesives. Glulam beams can be manufactured in curved shapes and enormous spans, making them ideal for large open spaces. In plyscraper construction, glulam typically serves as columns and beams that support CLT floor and roof panels.
Historic Milestones
The timeline of plyscraper development has accelerated rapidly in the past decade:
- 2017 – Brock Commons Tallwood House at UBC opens at 18 stories, becoming the tallest mass timber building in the world.
- 2019 – Mjostarnet in Norway claims the title at 18 stories with a mixed-use program including hotel and apartments.
- 2021 – The International Building Code approves provisions for mass timber buildings up to 18 stories across the United States.
- 2022 – Ascent Tower in Milwaukee rises to 25 stories, becoming the tallest mass timber building in the world.
Engineering and Performance Characteristics
Understanding how mass timber performs under real building conditions is essential for architects and builders considering plyscraper projects. The material behaves differently from steel and concrete in several important ways.
Structural Performance
One major advantage of mass timber is its strength-to-weight ratio. CLT and glulam are roughly one-fifth the weight of concrete of equivalent strength. This lightness reduces the load on foundations, leading to cost savings especially in seismic zones. Lower building weight also means less embodied energy during construction. However, tall timber buildings must be carefully designed to resist wind-induced vibrations, with engineers often combining timber with steel or concrete cores to achieve the required stiffness.
Fire Performance
The most common question about plyscrapers concerns fire safety. Mass timber behaves differently from dimensional lumber in fire conditions. When exposed to flames, the outer surface of a large timber member chars, forming a protective layer that insulates the unburnt wood beneath. This char layer maintains structural integrity for extended periods.
| Material | Behavior Under Fire | Structural Integrity After Fire |
|---|---|---|
| Mass Timber | Char layer forms; self-insulating | Maintained – char can be removed and member reused |
| Steel | Conducts heat; softens at high temperatures | Requires fireproofing spray or coating |
| Concrete | Slow heat transfer; spalling possible | Generally maintained but surface damage common |
Modern plyscrapers incorporate sprinkler systems, encapsulated timber, and redundant exit pathways to meet building code requirements. The 2021 IBC tall mass timber provisions include specific fire resistance ratings and sprinkler coverage requirements.
Acoustic Performance
Wood is naturally more porous than concrete, which raises questions about sound transmission. Mass timber buildings address this through layered floor assemblies with concrete toppings, acoustic mats, and resilient channels. These systems achieve sound ratings comparable to concrete construction. The natural warmth of exposed timber also provides psychological benefits – studies show occupants of mass timber buildings report lower stress levels and greater satisfaction with their spaces.
Environmental Benefits and Sustainability
The environmental case for plyscrapers is compelling. The building sector accounts for nearly 40 percent of global carbon dioxide emissions, with steel and concrete production contributing a significant share. Mass timber offers a path to dramatically reduce the carbon footprint of tall buildings.
Carbon Sequestration
Wood is the only structural building material that actively removes carbon from the atmosphere during production. Trees absorb CO2 as they grow, and that carbon remains stored in the timber even after harvest. A cubic meter of mass timber stores roughly one tonne of CO2. A 20-story plyscraper can lock away thousands of tonnes of carbon for the lifetime of the building, effectively turning the structure into a long-term carbon sink. One study found that replacing a concrete structural system with mass timber reduced embodied carbon by 45 to 55 percent.
Forest Stewardship
Responsible plyscraper construction depends on sustainable forestry. Mass timber products use smaller-diameter trees often thinned from overcrowded forests, improving forest health and reducing wildfire risk. The manufacturing process uses nearly the entire log. Certification programs such as the Forest Stewardship Council ensure timber is harvested from responsibly managed forests that maintain biodiversity and protect water quality.
Construction Efficiency
Mass timber buildings are assembled from prefabricated panels cut to exact specifications in a factory, then delivered for installation. This offers several sustainability advantages:
- Reduced waste – Factory waste rates below 5 percent compared to 20 percent for site-built concrete formwork.
- Fewer deliveries – A single truckload of CLT panels can replace ten concrete mixer trucks.
- Faster schedules – Prefabricated components install quickly, with some projects reporting 20 to 30 percent schedule reductions.
- Dry construction – No curing or drying time, allowing follow-on work to begin sooner.
Challenges and the Road Ahead
Despite the remarkable progress of the past decade, plyscrapers face real obstacles before becoming a mainstream building typology. The evolution of framing techniques over the centuries provides useful context for understanding where timber construction fits today, as explored in the Clearstory episode on how framing has changed across generations.
Cost Competitiveness
Mass timber construction costs vary significantly by region. In markets with established supply chains, plyscrapers compete with conventional construction on total installed cost. In regions where CLT and glulam must be imported, premium pricing of 5 to 15 percent is common. However, faster construction schedules reduce financing costs and interim interest. Lower foundation requirements can save hundreds of thousands of dollars. When these factors are included, mass timber often achieves parity with concrete and steel alternatives.
Building Code Evolution
The 2021 International Building Code marks a turning point for tall wood construction in the United States. New provisions for Type IV construction allow mass timber buildings up to 18 stories, with fire resistance ratings of 2 to 3 hours for primary structural elements. These changes followed rigorous testing by the US Forest Service and fire testing laboratories. Adoption varies by jurisdiction – some cities have embraced the new code language while others require additional review.
Moisture Management
Wood is hygroscopic, absorbing and releasing moisture in response to environmental conditions. During construction, exposed mass timber must be protected from rain with temporary enclosures. In service, the building envelope must prevent water intrusion and keep timber below 18 percent moisture content, where fungal decay cannot occur. These requirements are not unique to timber – steel must be protected from corrosion and concrete from freeze-thaw damage – but they demand careful attention from designers.
A Growing Pipeline
As of 2026, more than 100 mass timber buildings of seven stories or taller are in planning or under construction across North America. Major projects include the 21-story Haut tower in Amsterdam, a proposed 19-story mixed-use tower in Atlanta, and a planned 40-story tower in Vancouver that would push the boundaries further than any project to date. These projects, along with ongoing research, are building the evidence that plyscrapers are safe, sustainable, and economically viable. For building professionals, the message is clear: wood is not just for houses anymore.