A system for dispensing flame retardant foam on the exterior of a structure. The structure has an opening that enables distribution of flame retardant foam onto the roof. The system includes a foam distribution system having a foam expansion chamber and a roof plenum for delivery through the roof opening. Foam solution and compressed air are combined in a conduit and supplied to the foam expansion chamber. The structure may have at least one wall. In that case, the system may have a wall plenum for delivery of flame retardant foam from the foam expansion chamber through a first wall-associated opening. Each such wall will have an opening associated with the wall that enables distribution of flame retardant foam onto that wall.