We discussed “green roofs,” also known as vegetated roofs. A well-maintained green roof can reduce the threat of a roof fire since it contains a large amount of aggregate material that doesn’t burn. Those materials, such as crushed clay brick and pumice, expanded shale, and live plants, are largely resistant to fire. However, a drainage failure could add to the roof load, and dead plant material can itself become a source of combustion.
Roundtable attendees also talked about new exterior insulation panels made of plastic, such as expanded or extruded polystyrene. Those materials have many advantages: They are lightweight, made of recycled plastic, and have a high R-value (a measure of thermal resistance). However, most expanded plastics are combustible and can burn rapidly. Under fire conditions, those materials tend to melt, forming a flammable liquid.