What type of construction would be at greatest risk from an exterior fire?

• A. Type II
• B. Type III
• C. Wood Frame
• D. Heavy Timber

Answer: (C)

Wood frame construction is most vulnerable to an exterior fire because its structural framework is made of combustible wood throughout. When flames strike from the outside, the studs, joists, and sheathing heat up quickly, lose strength, and can fail, allowing the fire to spread rapidly through the walls and into the interior. The open, interconnected nature of a wood frame also provides many paths for heat and embers to move, making concealed spaces and gaps easy routes for the fire to extend.

In contrast, noncombustible exterior constructions (like Type II) resist ignition of the structural members, so exterior flames don’t as easily compromise the frame. Type III uses noncombustible exterior walls, which slows exterior flame intrusion, though interior wood components can still burn. Heavy Timber, with its large, solid timbers, chars and maintains structural integrity longer, providing more time for suppression.