What types of flat roof materials are commonly in use today?

Asphalt BUR with APP or SBS Cap sheet

Asphalt BUR (Built up Roof) with an APP (Atactic Polypropylene) modified bitumen cap sheet and loose aggregate is probably the most common type flat or low slope roofing material used today. SBS (styrene-butadiene-styrene) modified bitumen capsheets are also popular (on BUR applications), because they are more flexible than APP. More heat is required to install APP capsheets (vs SBS), but they are often still used because of the higher UV resistance and durability.

Below: A three dimensional cut-away of a BUR Roof (Built up Roof). APP (Atactic Polypropylene) or SBS (styrene-butadiene-styrene) are generally used as the capsheet, and normally loose gravel is used as a final layer.

Single Ply PVC and TPO Roofing

A few thermoplastic based single ply roofing materials are in fairly wide use as well: PVC (polyvinyl chloride based highly flexible plastic membranes) and TPO (thermoplastic polyolefin). These membranes become brittle with time, pulling away from the edges of a roof as they loose flexibility. And once a tear starts, it usually continues, meaning a small failure can easily turn into something much bigger.

PVC and TPO are two somwhat similar roof membranes. Both are flexible plastic based membranes that seal well, although eventually they fail when the plastic strinks, pulling away from the edges.

Foam Roofing

Sprayed Polyurethane Foam (SPF) is rising in popularity, although it holds a smaller segment of the market than more traditional roofing materials. This is a relatively newer technology, and in fact, 1 inch of foam is used on space shuttle fuel tanks to help keep them cool at 300 degrees below zero. SPF is similar to the insulating foam material used in refrigerators and is completely inert. The cost of an SPF roof is about the same as any other roof type when insulation is included. An SPF roof is a bit more expensive than a completely non-insulated roof.

Below: A closed cell polyurethane spray foam Eichler roof. Eichler roofs are popular because generally they have poor insulation if any and older Eichlers often have ponding or low spots which polyurethane foam can correct. Most importantly, foam lasts the life of the roof with little or no maintenance.



SPF (sprayed polyurethane foam) roofing is a plastic based, closed cell, rigid type of roof insulation, which is usually coated with an acrylic based elastomeric coating. This type of foam is nothing like the type you’ll find in a couch cushion or bed; those are both low density open cell based types of foam. Polyurethane foam is closed cell based, with about 1 million cells per square inch, and durable. Walking on an SPF roof feels somewhat like walking on a concrete sidewalk. Polyurethane sprayed foam is unique, in that it is manufactured on site, and to get best results, it is best if the contractor has a proven track record in SPF (Sprayed Polyurethane Foam) applications. Otherwise, hidden mistakes can compromise the roof. Assuming a skilled contractor is used, sprayed polyurethane foam (SPF) is the most superior flat roof solution. A sprayed foam roof is seamless, highly insulated, and can last the life of a building.

Polyurea Roof Coatings and Sealants

Polyurea is also a newer technology which is growing in popularity for roof coating applications. Polyurea is formed by the reaction of an isocyanate component and a synthetic resin blend component. Most commonly, polyurea is often used for coating spray foam roofs. Some formulations of polyurea meet “cool roof” Energy Star ratings for color and reflectivity. Polyurea is also often used as a solution for repairing leaky metal roofs. Polyurea is flexible enough to handle the natural expansion and contraction of metal roofs with tearing.

Polyurea, due to high elongation, tensile strength, fast cure time, and water resistance, is often used as joint fill or caulking to seal and repair many types of failing roof membranes or surfaces. Polyurea is resistant to many fuels and chemicals making it useful in many other applications including fuel tank linings, aquarium lining, landscape water containment (artificial ponds), and even manhole and sewer linings.

Foam Roofing is Green & Helps Save the Environment

As people become more educated about the importance of 'green roofing', SPF has been growing in popularity. The quality of living in a flat roof home without much insulation, and without reflective roofing material is drastically different from a flat roof home with a seamless, sprayed polyurethane foam roof with reflective coatings. In this scenario, a flat roof home with 2" to 2.5" of foam can easily save 25% to 40% in energy costs vs a home without much insulation. Long term, any foam roof will eventually pay for itself. It really just depends on how expensive gas and electric heating & cooling costs are in comparison to the size of the roof, and several other factors. Keeping a home cool in summer and warm in winter is relatively easy with a polyurethane foam roof. If every home in the USA used polyurethane foam roofing, energy usage and associated fossil fuel consumption could be cost by as much as 25% to 40%! Now this is something that can really contribute to saving our environment, and improving the quality of living in our homes at the same time.

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This article really increase my knowledge.

akismith678 wrote:This article really increase my knowledge.

Writing these articles increased my knowledge as well. We do appreciate the positive feedback. We hope to help people make more informed roofing and solar related decisions.