What is Mass Timber Construction?
The term “mass timber” is used to describe a variety of engineered timber products that combine laminations and compression of multiple layers to create solid panels of wood and achieve greater strength than traditional dimensional lumber. It is commonly used in building’s walls, floors and roofs and is seen as a sustainable and more carbon-friendly alternative to steel and concrete. It also includes innovative forms of sculptural buildings, and non building structures formed from solid wood panel or framing systems of six feet or more in width or depth.
Mass Timber Product Types
- Nail-laminated timber (NLT or nail-lam) is created from individual dimension lumber members stacked on edge and fastened with nails or screws to create a larger structural element. It is a century-old construction method that is undergoing a design renaissance. It can be found today in many historical buildings as well as in compelling new projects of all sizes, where its structural performance and design elegance come together to create inspiring spaces. Advantages of NLT include the ability to use locally available wood species and the fact that specialized equipment generally isn’t necessary.
- Cross-laminated timber (CLT) is a wood panel system that is gaining in popularity in the U.S. after being widely adopted in Europe. It consists of layers of dimension lumber (typically three, five or seven) oriented at right angles to one another and then glued to form structural panels with exceptional strength, dimensional stability and rigidity. CLT is the basis of the tall wood movement, as the material’s high strength, dimensional stability and rigidity allow it to be used in mid- and high-rise construction. CLT is well suited to floors, walls and roofs, and may be left exposed on the interior for aesthetics. Because of the cross-laminations, if offers two-way span capabilities.
- Dowel-laminated timber (DLT) is common in Europe and is gaining traction in the U.S. for its ease of use with computer-controlled (CNC) machinery—such as lathes, routers and mills—and its all-wood composition. DLT is similar to nail-laminated timber (NLT). Instead of nails or screws, however, DLT uses hardwood dowels to join laminations. Among the advantages of DLT, acoustic strips can be integrated directly into the bottom surface of a panel.
- Glue-laminated timber (glulam) is composed of individual wood laminations selected and positioned based on their performance characteristics, and then bonded together with durable, moisture-resistant adhesives. The grain of all laminations runs parallel with the length of the member. It is commonly used for beams and columns in residential and commercial applications. Glulam is a highly visible form of mass timber in contemporary projects, with long spans framing signature designs that have been left exposed to take advantage of wood’s natural aesthetic. It has excellent strength and stiffness properties and is available in a range or appearance grades for structural or architectural applications.
- Structural Composite Lumber (SLC) is a family of wood products created by layering dried and graded wood veneers, strands or flakes with moisture-resistant adhesive into blocks of material which are subsequently re-sawn into specified sizes. Two SCL products – Laminated Veneer Lumber (LVL) and Laminated Strand Lumber (LSL) are relevant to the mass timber category as they can be manufactured in panels in sizes up to eight feet wide, with varying thicknesses and lengths. Parallel Strand Lumber (PSL) columns are also commonly used in conjunction with other mass timber products.
- Wood-Concrete composites are a hybrid option for wood high-rises, very long spans, or other project- specific requirements. Typically, on top of a wood slab there is a connected concrete layer working in compression. It also has better acoustic properties than conventional timber floors.
Mass Timber Buildings
T3 Minneapolis
Location: Minneapolis, United States Designed by Michael Green Architecture (MGA) and DLR Group for real estate firm Hines, T3 — short for “Timber, Technology, Transit” — is a seven-story, 220,000-square-foot structure. It’s currently the tallest mass timber building in the United States, at 138 feet. |
Stadthaus Tower
Location: Hackney, England Stadthaus is a nine-story residential building and the second tallest timber residential structure in the world. Stadthaus is the first high-density housing building to be built from pre-fabricated CLT panels. It’s also the first building in the world of this height to construct stair and lift cores entirely from timber. |
Mjøstårnet
Location: Brumunddal, Norway Mjøstårnet is a 280-foot-tall tower constructed entirely out of cross-laminated timber. It’s all wood—even it’s elevators are built from CLT, and its large-scale interior trusses are glulam. The architects used locally-sourced materials to build the soaring structure, which features a series of wooden fins on its western facade and an open- air rooftop with a sculptural timber topper. |