Final answer:
Foam plastic must be separated from the building by an insulation layer of at least 1/2" gypsum board, mainly for fire resistance rather than thermal insulation. Polystyrene and EPS are good insulators due to their air pockets that impede heat conductivity.
Step-by-step explanation:
Unless otherwise allowed, foam plastic shall be separated from a building by an insulation layer of not less than 1/2" gypsum board. This requirement is detailed in building codes and regulations to enhance fire safety and prevent the quick spread of fire through combustible materials like foam insulation.
Foam plastics like polystyrene and expanded polystyrene (EPS), commonly referred to as Styrofoam, are well-known for their insulating properties. These materials contain many small pockets of air, which is a poor conductor of heat, thus significantly enhancing their insulation capabilities.
The role of the 1/2" gypsum board as an insulation layer is not primarily for thermal insulation, but for fire resistance. Gypsum board is composed of gypsum encased in paper, which can provide a physical barrier that slows down the spread of fire. This is particularly important when dealing with foam plastics, which can be highly flammable and thus pose a significant hazard in building construction without proper fire barriers.
Not only does a proper insulation layer help in maintaining the thermal efficiency of a building by reducing heat transfer between the interior and exterior, but it also enhances fire safety, potentially saving lives and preventing property damage.