Cavity Barriers are pieces of fire stopping material. They are fitted within the cavity of a building at each floor horizontally and vertically around windows. The material provides compartmentation. This means that both the flames and heat cannot be transferred to other compartment areas. Throughout the life of the building, the Cavity Barrier will remain fixed in place. In the event of a fire, the intumescent material expands and seals off the gaps. Additionally, the horizontal barriers allow for a ventilation gap within the cavity. This will be closed when the intumescent expands.