What is mass timber?

Mass timber refers to a category of framing styles characterized by the use of large, engineered wood panels, often paired with engineered wood columns, and beams. Panels are most frequently used in horizontal applications for floors and roofs, but can also be used vertically for walls.

It is common to use mass timber in combination with other building systems to achieve benefits greater than those offered by each system alone. Examples include mass timber floors and roof with light-frame wood walls, steel elements in long-span floor systems, and concrete foundations, podiums, cores, and floor toppings.

The term heavy timber is typically associated with large cross sections of solid sawn members (beams, purlins and columns), often using tongue-and-groove decking for floors and roofs. Heavy timber is not covered in this document.

More about Glulam and GLT

• Can be fabricated in almost any shape, though straight elements are most common; jigs may be used to form curves, bends, and different radii
• Typical glulam beam and column sizes: 6 to 72 inches deep and up to 100 feet long
• Typical GLT panel sizes: 2 to 4 feet wide and up to 60 feet long
• Beams and columns more common than planks
• Plank design requires consideration of design stresses, layups, lumber species, and grade

Code Path

Glulam and GLT have the same code references and manufacturing standards. They are permitted under IBC Section 2303.1.3 when manufactured and identified as required in the ANSI 190.1 Product Standard for Structural Glued Laminated Timber and ASTM D3737 Standard Practice for Establishing Allowable Properties for Structural Glued Laminated Timber (Glulam).

For more information, APA – The Engineered Wood Association offers a variety of glulam-specific materials in its resource library.

More about NLT

• Historically used for warehouses and other large buildings
• Typical panel size: 2 to 4 feet wide and 16 to 40 feet long
• Typically fabricated offsite; onsite fabrication possible for experienced contractors but not common
• Different visual profiles (such as alternating lumber sizes) used to achieve acoustic or other objectives

Code Path

NLT is recognized prescriptively as mechanically-laminated decking in Chapter 23 of the IBC.

More about SCL

SCL products used in column and beam applications include:

• Laminated veneer lumber (LVL) is made by bonding thin wood veneers so the grain of all veneers is parallel to the long direction
• Parallel strand lumber (PSL) is manufactured from veneers clipped into long strands and oriented primarily along the strong axis
• Laminated strand lumber (LSL) is made from flaked wood strands
• Oriented strand lumber (OSL) is made from flaked wood strands with a smaller length-to-thickness ratio than LSL

Code Path

SCL products are permitted under the IBC Section 2303 when manufactured according to ASTM D5456: Standard Specification for Evaluation of Structural Composite Lumber Products.