Mass Timber
Large engineered wood panels and beams that act as a building's structure.
Quick Answer
Mass timber is a category of large, solid engineered wood products, including cross-laminated timber (CLT), glue-laminated timber (glulam), nail-laminated timber (NLT), and dowel-laminated timber, used as structural floors, walls, beams, and columns. Prefabricated off site, it can build mid-rise and tall buildings and, under the code, can achieve required fire-resistance ratings through charring.
The Full Picture
Mass timber refers to structural elements made by layering or joining many pieces of lumber into large, solid members. Cross-laminated timber (CLT) panels stack boards in alternating directions and glue them. Glulam beams and columns bond laminations in the same grain direction. NLT and dowel-laminated timber fasten boards with nails or wooden dowels. Mass plywood panels are a newer entry.
These products are manufactured in plants to precise dimensions, often with openings and connection preparations cut by CNC machines, then shipped and assembled on site, usually with a crane. Prefabrication shortens the site schedule, produces little waste, and lets the structure be left exposed as a finish, though moisture protection during construction is a major concern.
Fire behavior is central to code acceptance. Large timber chars on the surface at a predictable rate, which insulates the interior, so designers can provide required fire-resistance by sizing members with extra thickness and by adding protection such as gypsum board. The International Building Code includes Type IV construction categories for mass timber, which allow taller and larger buildings than light wood framing.
For contractors, mass timber raises early-engagement needs: long lead times, manufacturer-specific design and detailing, connection hardware, crane and delivery logistics, weather protection, and coordination with MEP rough-ins, which have to be planned before panels are fabricated. Estimators generally price it as a specialty package from supplier quotes and drawings, and carbon and sustainability goals are often a reason owners choose it.
Real Examples
Common Misconceptions
People assume: Wood buildings cannot be tall or fire-safe.
Actually: Modern codes include mass timber construction types with fire-resistance requirements, and the charring behavior of large timber is accounted for in design. Height and area limits still apply under the code.
People assume: Mass timber is built just like conventional wood framing.
Actually: It is closer to precast or steel in delivery: prefabricated, tightly planned, crane-erected, and dependent on early coordination and supplier-specific detailing.
Frequently Asked Questions
What are the main types of mass timber?
Cross-laminated timber (CLT), glue-laminated timber (glulam), nail-laminated timber (NLT), dowel-laminated timber (DLT), and mass plywood panels.
Is mass timber fire-resistant?
Large timber members char at a predictable rate, which protects the inner core, and the building code's mass timber construction types set fire-resistance requirements that designs must meet, sometimes with added gypsum protection.
Why is mass timber used?
Reasons include faster site assembly through prefabrication, lower embodied carbon compared with some other materials when sustainably sourced, and the appearance of exposed wood. Suitability depends on the project and code limits.
What should contractors plan for with mass timber?
Long lead times, supplier-specific detailing, early MEP coordination, crane and delivery logistics, and moisture protection of the wood during construction.