Fire Requirements for Mass Timber Elements: Code Applications, Construction Types, and Fire Ratings

For many years, exposed heavy timber framing elements have been permitted in U.S. buildings due to their inherent fire-resistance properties. The predictability of wood’s char rate has been well-established for decades and has long been recognized in building codes and standards.

Today, one of the exciting trends in building design is the growing use of mass timber—i.e., large solid wood panel products such as CLT and NLT for floor, wall, and roof construction. Like heavy timber, mass timber products have inherent fire resistance that allows them to be left exposed and still achieve a fire-resistance rating (FRR). Because of their strength and dimensional stability, these products also offer an alternative to steel, concrete, and masonry for many applications, but have a lower carbon impact. It is this combination of exposed structure and strength that developers and designers across the country are leveraging to create innovative designs with a warm yet modern aesthetic, often for projects that go beyond traditional norms.

Developed for architects and engineers seeking foundational content on mass timber building design, this paper covers:

• Allowable uses of mass timber by construction type
• Heavy timber requirements
• FRR requirements
• Selecting a construction type
• Methods of demonstrating mass timber FRRs
• Fire protection of penetrations
• Fire protection of connections
• Interior finish requirements