Ordinary roof coverings may be applied over foam plastic when the foam is separated from the interior of the building by plywood sheathing at least ______ thick.

Ordinary roof coverings may be applied over foam plastic when the foam is separated from the interior of the building by plywood sheathing at least ______ thick.

• A. 1/4 inch
• B. 1/2 inch
• C. 3/4 inch
• D. 1 inch

Answer: (B)

The key idea is fire protection between the foam plastic insulation and the interior. When foam plastic is used, an ordinary roof covering can be placed over it only if there’s a fire barrier separating the foam from the living space. A minimum of half an inch of plywood acts as that barrier, providing enough heat resistance and structural support for the roof assembly. thicker plywood would also meet the requirement, but 1/2 inch is the minimum.

The key idea is fire protection between the foam plastic insulation and the interior. When foam plastic is used, an ordinary roof covering can be placed over it only if there’s a fire barrier separating the foam from the living space. A minimum of half an inch of plywood acts as that barrier, providing enough heat resistance and structural support for the roof assembly. thicker plywood would also meet the requirement, but 1/2 inch is the minimum.