In Type III construction, which feature can spread fire unless fire stops are installed?

• A. Nonoperating windows or other openings
• B. Open web joists supporting metal roof decks
• C. Void spaces inside wooden channels in the roof
• D. Foam insulation sandwiched between sheets of plywood

Answer: (C)

In Type III construction, hidden voids within the roof structure can act as uninterrupted channels for flame and hot gases to travel, letting a fire spread rapidly from one part of the attic or ceiling cavity to another. The feature described—void spaces inside wooden channels in the roof—creates those concealed pathways. When fire stops are not installed to interrupt and seal these channels, the fire can move through the roof assembly more easily, bypassing interior barriers and delaying detection or containment.

Fire stops are installed to break the continuity of these cavities, effectively slowing or halting the spread of fire through concealed spaces. The other options involve openings or materials that contribute to fire spread in different ways, but the key risk that fits the scenario is the presence of wooden roof channels with voids that need fire stops to prevent rapid vertical and horizontal fire progression.