All roofs feature some slope to allow for drainage. Low-slope—sometimes referred to as “flat”—roofs generally feature a very slight slope of less than 3:12. Slopes are represented as a ratio of how much the roof rises (vertical) over the distance (horizontal) between its lowest edge and its highest edge. A 3:12 slope indicates a rise of 3 inches over a 12-inch distance.
There are a number of different low-slope roof systems, including:
- Built-up Roof (BUR) Membrane Systems. Built in several layers, including insulation board, perlite, inter-ply sheets, asphalt, and pea gravel ballast repeated in various combinations
- Polymer-Modified Bitumen Sheet Membrane Systems. Built with reinforced bitumen membrane fabrics that are either mopped on using hot asphalt, heat welded, or torch applied
- Spray Polyurethane Foam-Based (SPF) Systems. Built by spraying foam consisting of heated and properly proportioned isocyanate and polyol
- Single-Ply Membrane Systems. Built by applying a single layer over a roof structure or insulation board
The following blog post discusses each of the three types of single-ply roofing systems, outlining their characteristics, applications, and advantages and disadvantages.
Types of Single-Ply Roofing Systems
Single-ply roofing systems utilize flexible sheets of thermoset or thermoplastic membranes. Both membranes offer unique advantages and disadvantages. For example, thermoplastics are highly reusable as they can undergo melting numerous times, while thermosets remain in a solid state after curing. The three main types of compounds used in single-ply membrane systems are:
- Ethylene propylene diene terpolymer (EPDM): a thermoset
- Polyvinyl chloride or polymerized vinyl chloride (PVC): a thermoplastic
- Thermoplastic polyolefin (TPO): a thermoplastic
Composed of two main ingredients—i.e., ethylene and propylene (derived from oil and natural gas)—EPDM is a synthetic rubber. EPDM roofing membranes come as large, black or white rolls with widths ranging between 7.5–50 feet (10 feet being the most common) and thicknesses of 45, 60, or 90 mils. Roof systems which use this material typically have life spans ranging between 10 and 25 years.
Common installation methods include full adhesion, mechanical attachment, or ballasting followed by gluing or taping of the seams. As the EPDM material is available in large rolls, it is an ideal roofing solution for large commercial buildings, such as warehouses, office buildings, hotels, shopping centers, large retail stores, schools, and universities.
Advantages of EPDM roofing systems include:
- Resistance to hail and abrasion
- Durability under extreme weather conditions
- Flexibility in cold weather climates
- UV radiation resistance
- Flexible membrane allows for easier installation, especially at flashings and penetrations
Disadvantages of EPDM roofing systems include:
- It tends to absorb more heat, leading to a higher risk of structural overheating in extreme heat.
- It punctures easily, so walking on it should be limited or avoided.
- It shrinks in dry, hot climates.
PVC is a synthetic, thermoplastic polymer composed of polyvinyl chloride. It exhibits several advantageous material properties, including resistance to wind, moisture, fire, and chemicals. PVC roofing material usually comes in rolls of 50–100 feet long and 5–12 feet wide. It is installed using full adhesion, mechanical fastening, or ballasting and seam welding methods.
The lifespan of a PVC roof system installation ranges between 15 and 30 years. As the roofing material is packaged in smaller rolls than EPDM roofing systems, it is easier to install. This quality also makes this roofing system suitable for smaller commercial and residential installations.
Advantages of PVC roofing systems include:
- High strength (up to 350 pounds per square inch breaking strength)
- Durability due to welding of seams rather than using tapes or liquid adhesives
- Superior resistance to moisture, wind, fire, and chemicals
- Versatility (can be used for patios, decks, and balconies with added non-slip coating)
- Reflective surface
Disadvantages of PVC roofing systems include:
- Its material costs tend to be higher.
- May lose reflectivity over time due to excessive air pollutionLess flexible membrane can make for a more laborious installation, especially at flashings and penetrations.
TPO Membrane Roofing
TPO membrane roofing systems are rapidly growing in popularity in the commercial roofing market. These systems feature a single layer of synthetic thermoplastic combined with reinforcing scrim that provides a naturally reflective surface that resists UV radiation penetration and wear. The roofing material is available in rolls with widths of 10, 12, or 20 feet and installed using mechanical or adhesive attachment with heat-welded seams.
A TPO membrane roofing system’s life span ranges from between 7–20 years. As TPO roofing material has similar roll sizes to EPDM roofing systems, their applications overlap.
Advantages of TPO roofing systems include:
- Reflective surface (suitable for preventing UV radiation wear or exposure)
- High strength (3–4 times stronger than EPDM, but not quite equal to PVC)
- Durability (due to welded seams)
- Excellent wind resistance
- Low cost material
Disadvantages of TPO roofing systems include:
- Like PVC, a less flexible membrane can make for a more laborious installation, especially at flashings and around penetrations.It has a short life span.
Contact Knickerbocker for Your Roofing Needs
At Knickerbocker Roofing and Paving Co., Inc., we provide a broad range of low-slope roofing systems for commercial, industrial, and historical building applications, including EPDM, PVC, and TPO roofing systems. We offer a two-year contractor guarantee on our work as well as 5 to 30 year manufacturer’s warranties on the products we handle.
To maintain our position as a leader in the roofing, sheet metal, and waterproofing industries and ensure the quality of our solutions, we:
- Perform all roofing, sheet metal, and carpentry work in-house using our expert team
- Maintain certifications from all major roofing system manufacturers to furnish and install their systems
- Perform project safety inspections with an independent safety consultant
- Offer roof inspections and evaluations at no cost
- Run annual roofing application and safety training programs