Foam plastic insulation must be separated from a plenum by what?

Foam plastic insulation must be separated from a plenum by a thermal barrier to ensure safety and compliance with building standards. A thermal barrier serves to protect the foam from high temperatures that could lead to ignition. This is crucial because foam plastics can present a fire hazard if exposed directly to the high temperatures found in plenum spaces, which are often used for air circulation in buildings.

The thermal barrier typically consists of materials like gypsum board that can withstand fire and help to maintain a safe environment. This requirement is especially important in maintaining fire safety and preventing potential fire spread through the building's air distribution system.

While air barriers, vapor barriers, and fireproof barriers all play important roles in building construction and performance, they do not specifically address the heat and combustion concerns that necessitate the use of a thermal barrier in this context.