What must be installed to protect foam insulation in unventilated crawl spaces?

To protect foam insulation in unventilated crawl spaces, a thermal barrier or ignition barrier must be installed. This is crucial because while foam insulation is effective in thermal resistance, it is also flammable under certain conditions. An ignition barrier serves to prevent the foam from igniting and can slow down the spread of flames, thereby enhancing the overall safety of the building.

Installing a thermal barrier, such as drywall, over the foam insulation reduces the risk of fire and helps to fulfill building code requirements, which often mandate that foam insulation be covered when installed in certain locations. This ensures that the insulation is shielded from direct exposure, providing a level of protection against ignition sources and maintaining safety standards.

In contrast, while a moisture barrier is important in controlling moisture, it does not address the fire safety concerns associated with foam insulation. Similarly, a structural barrier may prevent physical damage but does not mitigate fire hazards, and an air barrier primarily focuses on controlling air movement but does not fulfill the fire protection requirements necessary for foam insulation. Thus, the necessity for a thermal or ignition barrier is paramount in these specific applications within unventilated crawl spaces.