Engineering Wood Resins: A Commonly Misunderstood Fire Hazard

The rise of mass timber and engineered wood is rapidly transforming the landscape of industrial, commercial, and institutional construction. The benefits are well known: accelerates construction, reduced carbon footprint, prefabrication, structural performance, and, in many cases, excellent fire resistance.

However, this trend raises certain recurring questions among underwriters and risk managers regarding the risks associated with their manufacture. One such question concerns the flammability of the resins used in the manufacture of engineered wood.

The subject warrants clarification, as many perceptions remain inaccurate. The term “resin” is often mistakenly associated with a liquid such as a glue made from a flammable solvent. The reality is generally much more nuanced.

Understanding the Nature of the Resins Used

Engineered wood products—such as glued-laminated timber, CLT (cross-laminated timber), or certain structural panels—use various resins as bonding agents between the wood fibers or layers. Many of these resins are polymers: long, flexible molecular chains, similar to several types of industrial plastics.

Unlike a conventional flammable liquid such as a solvent-based adhesive, these resins do not contain a base designed to evaporate quickly to facilitate drying. Polymer-based resins therefore do not behave like a liquid fuel that could rapidly and violently ignite when exposed to a low-energy ignition source. Although they can burn (like most plastics), their thermal behavior when ignited is different.

Compared to a flammable liquid, many of these polymer-based resins tend to undergo thermal decomposition. When exposed to heat, they bake, char, or solidify rather than rapidly generating flammable vapors, as might occur with an adhesive or a solvent-based product, for example.

Some formulations may indeed contain liquids that could be ignited. However, these components are generally present in low concentrations within the final mixture, and their ability to sustain a fire is low.

From a risk assessment perspective, it is therefore generally more appropriate to consider polymer-based resins as plastics (in a viscous form, such as molasses) rather than as flammable liquids.

This distinction is important because it directly influences:

• Fire risk analysis;
• Storage criteria;
• Fire spread scenarios;
• Fire protection requirements;
• Insurers’ perception of risk.

The actual hazard does not necessarily lie in the rapid ignition of the resins themselves, but rather in the overall behavior of the structural assembly when exposed to a major fire.