Flat roofing will include Built Up Roofing, Single Ply Flat Roofing, Spray Foam Roofing, and Roof Coatings. Built Up Roofing will include a system of multiple layers like Modified Bitumen. Single Ply Roofing will be installed as fully adhered/glued or it will be mechanically fastened. Spray Foam Roofing will include a two part insulation which is sprayed directly onto the roof and then coated with acrylic or urethane coating. A thin layer of crushed stones and sand is then also applied. These types of roof coatings are made for existing roofs and will usually extend the life of your roof by 10 to 15 years.