Choosing The Right Covering For Your Low-Slope Or Flat Roof

If you look carefully at buildings in your area, you will likely see many low-slope or flat roofs. These roofs — where the slope rises less than four inches in a run of 12 inches — need special systems to prevent leaks. And whether the roof protects a giant industrial building or your home, you want to choose the best roofing material for your low-slope or flat roof structure. Here’s how. 

Today, low-slope or flat roofs are commonly covered with one of four main material types: TPO, PVC, EPDM or modified bitumen. Historically, built-up roofing (or BUR) was very popular for flat roofs. Here is a closer look at roofing options: 


Thermoplastic polyolefin (TPO) is a single-ply membrane with many terrific characteristics for a low-slope or flat roof. Because it’s a plastic material, the seams can be welded for extreme durability. When thinking about high temperatures and direct sunshine on the roof, like in the Clearwater area, you can choose TPO in white for its reflectivity and ability to keep the interior of the building cooler than black or other dark hues. It does well in the weather, offering the flexibility to withstand building settlement and thermal expansion/contraction. TPO resists punctures and, while not impervious, it can handle moderate hail.


Before TPO, polyvinyl chloride (PVC) was the top choice for single-ply low-slope or flat roofing. TPO shares many qualities with PVC. Architects and building professionals used PVC as an alternative to tar and gravel systems (also known as built-up roofing or BUR). Because it’s also flexible, suitable for heat welding and is cool-roof qualified, PVC’s true advantage over TPO is the ability to withstand a large range of chemicals. PVC makes for a quality membrane roof covering for restaurants with kitchen vents that penetrate a low-slope or flat roof, because PVC is impervious to grease and oil. 


Ethylene propylene diene terpolymer (EPDM) brings several great qualities to any low-slope or flat roof system. It is a modified rubber material and is very flexible. EPDM can withstand decades of hot/cold cycles and differential settling of the building without difficulty if it is fully bonded to a low-slope or flat roof. 

EPDM can tolerate nearly any chemical, and is the same material used to line leach pits and retention ponds. Although the most-used color is black, EPDM also comes in white. EPDM can handle hail better than other single-ply membranes. Because it is a rubber product, EPDM resists punctures under ordinary conditions. Gravel, embedded in shoe soles, can cut the membrane, so it may not work well where there could be heavy foot traffic.

Modified Bitumen or AAP

Modified bitumen, also known as atactic polypropylene (APP) or “mod bit,” is another single-ply material for a low-slope or flat roof. Modified bitumen is an asphalt product that is less expensive than plastic and rubber membranes. It can hold up as long as the roof never sustains pooling water. Options include a torch-down — where the crew melts the back with a torch as they roll it out — or unraveling and sticking a self-adhering membrane. As the most up-front economical choice, it will require replacement more often. Mod bit has many color options, so you can match a sloping porch cover to your pitched roof’s shingles.

Built-Up Roofing

Built-up, or tar and gravel, roofing has served property owners well for over a century. It’s made with several layers of reinforced felt, or scrim, combined with hot liquid asphalt and topped with pea gravel for UV protection. As a roof system, it has proven itself quite durable and hail-proof. BUR mandates the use of a kettle to melt the asphalt. This brings considerable risks when choosing this system. However, for very large low-slope or flat roofs, BUR can save your budget and last longer than any single-ply materials.

New Help With a Low-Slope or Flat Roof? 

John Hogan Roofing is an expert low-slope and flat roof contractor with 25 years experience. Whether you need a roof repair or a complete roof installation, we have the solution for you. Contact us today to get a free estimate and protect your property.