Under fire conditions, plywood I-beams used in Type V construction tend to do what compared with solid lumber?

• A. Are extremely stable and resistant to collapse
• B. Fail and burn much more rapidly than solid lumber
• C. Produce ventilation-limited conditions and backdraft
• D. Prevent fire travel due to the lack of voids or concealed spaces

Answer: (B)

Under fire exposure, plywood I-beams in Type V construction burn and lose strength much faster than solid lumber because they are engineered, lightweight members with a thin, exposed web and glued laminations. The higher surface-area-to-volume ratio means more of the wood is exposed to heat at once, and the adhesives used to bond plywood degrade quickly in flames. As the web and joints burn away, the cross-section that resists bending collapses rapidly, leading to sudden failure. Solid lumber, while combustible, chars at a slower, more predictable rate and retains enough cross-section longer to resist collapse, delaying failure compared with the engineered plywood I-beams.