The Other Tall Building System
A fast-growing circle of building designers of mid-rise (six to 12 stories) and tall buildings (up to 30 stories) have begun to specify a new building system that is the first viable alternative to concrete and steel mid-rise and tall building structures.
The performance of this new building system meets or exceeds current material systems in strength-to-weight ratio and yet is just 25 percent of current material systems weight. Its safety record for seismic, fire, and wind resistive performance is proven and established. Structures built with the system can generally be erected much more quickly than structures made from other materials. The sustainability benefits of the system are unmatched.
This crucial building material is, of course, mass timber.
The performance and safety characteristics of mass timber products have captured the imagination of architects worldwide. The evidence of this growing phenomenon is mounting, from a 12-story mixed development project in Oregon, and a 10-story residential building in New York, to a 24-story, 200,000-square-foot commercial and residential tower in Vienna, Austria. Today, dozens of tall wood projects are being specified worldwide.
The growing array of mass timber products makes possible building design far beyond the scope of dimensional lumber. Some of those advantages include:
- Reduced carbon footprint and embodied energy help maintain sustainable development and mitigate climate change.
- Supported by building science and vetted for full scale fire, seismic, durability, acoustic, and vibration by teams of independent researchers and engineers worldwide.
- Compliance with all performance requirements expected for any mid-rise or tall building system.
- Cost parity with concrete and steel construction systems thanks to prefabricated mass timber components that typically increase construction speed, reduce labor costs, and accelerate owner ROI.
- Locally-sourced, which can lower transportation costs.
- Simplified reclamation/recycling at the end of the building’s service life.
- Enables resilient design by meeting demanding earthquake and seismic safety requirements.
As local project conversations shift to include mass timber as a viable alternative, it’s important to understand the products that form the heart of the system. Improved understanding can help better inform local code-setting discussions and decision-making. Today, many jurisdictions have implemented or are in active discussion to set appropriate code requirements, observing the latest (2015) International Building Code (IBC) guidelines and ANSI/APA standards (ANSI/APA Section 2303.1.4).
The distinction of ‘combustible verses non-combustible construction’ has restricted the development of mass timber technologies for the construction of taller structures. However, new technologies, products, and systems are available today that weren’t available or as well understood in the past. Scientific research and testing over the past five years, as well as the construction of more than 17 tall mass timber buildings (seven stories or taller) around the world, has provided building officials, designers, contractors, and consumers’ confidence that these buildings are safe and resilient. For the latest wood research visit our research page.
Tall buildings are a vital element in any urban setting as they make the best use of limited space. Compact cities promote sustainable transportation methods such as walking, cycling, and public transportation. Tall buildings also have the ability to be more energy efficient than single family residences through the use of efficient central services and higher overall building volume to surface ratios (shared floors/ceilings, minimal weather exposed surfaces).
The mass timber family includes six products. Each product shares common characteristics of strength and predictability, and all products deliver versatility and performance with a low carbon alternative. Here’s a brief look at three:
Nail Laminated Timber (NLT or Nail-lam)
- Composition. Fasten individual dimensional lumber, stacked on edge, into one structural element with nails.
- Aesthetics. NLT offers a consistent and attractive appearance for decorative and exposed-to-view applications. Sheathing can be added to the top side to provide a structural diaphragm, allowing use as a wall panel element.
- Uses. Floors, decks, and roofs, in addition to timber elevator and stair shafts.
Glued Laminate Timber (Glulam)
- Composition. Individual wood laminations selected for performance characteristics are bonded together with durable, moisture-resistant adhesives. Laminations run parallel with the member length. Glulam is available in depths from six to 72 inches and can exceed lengths of 100 feet.
- Aesthetics. Available in a range of appearance grades for structural or architectural applications.
- Uses. In horizontal applications glulam is often used as a beam. In vertical applications, it serves as a column.
Cross Laminated Timber (CLT)
- Composition. Three, five, or seven layers of dimension lumber oriented at right angles to one another and glued to form structural panels with exceptional strength, dimensional stability, and rigidity. Can be manufactured to customized dimensions. Panel sizes vary by manufacturer. Length is usually limited by transportation restrictions.
- Aesthetics. CLT may be left exposed in structure interiors. It differs from glulam in that glulam is layered with the grain.
- Uses. CLT panels resist high racking and compressive forces, making them especially cost effective for multi-story and long-span diaphragm applications. Well-suited for floors, walls, and roofs. CLT panels are used in prefabricated building components or for off-site construction.
Advances in wood connectors, hybrid materials and building systems (using wood, concrete, and steel), the commercialization of CLT, and off-site prefabrication have all provided more options for the safe and effective design and construction of taller mass timber buildings.
Wood buildings typically cost less—economically and environmentally―while delivering more in terms of its beauty, versatility, and performance. Wood can also be a low carbon alternative to steel, masonry, and concrete in many applications.
Explore the rest of the reThink Wood website for more information, the latest research and news on mass timber.
The ICC Board of Directors has created and appointed an ad hoc committee to explore the building science of tall wood buildings. The first meeting of the committee is scheduled for July 6 - 8 in Chicago. More information and other related materials are available on the Ad Hoc Tall Wood Buildings site at http://www.iccsafe.org/codes-tech-support/cs/icc-ad-hoc-committee-on-tall-wood-buildings/.