Wooden trusses with gusset plates fail unless they are protected by?

• A. Fire resistant material
• B. Water coating
• C. Steel sheath
• D. Insulating foam

Answer: (A)

The main idea is that protecting wooden trusses with gusset plates from heat is essential to prevent rapid structural failure. The gusset plates connect the lumber members, and in a fire the wood near these joints can burn or lose strength quickly, and the plates can weaken as heat conducts through. By applying a fire-resistant covering, heat transfer to the gussets and surrounding wood is slowed, buying time for occupants and firefighters and helping to keep the roof structure from collapsing as quickly.

In practice, this means using a certified fire-resistant material on the underside of the trusses or within the attic space—materials like gypsum board or other approved fire-resistant coverings that meet the required rating.

Other options aren’t effective: a water coating isn’t practical for ongoing protection in a fire and can cause damage as it evaporates and creates steam; a steel sheath would alter the structure and isn’t a standard protective method for this issue; insulating foam is flammable and could actually worsen fire spread.