The first single-ply roofing membrane was introduced to the commercial roofing industry in the 1960s. Thanks to their reliability, ease of installation, and longevity, single-ply roofing systems have become popular among commercial roofing contractors. Today, various types of single-ply material exist, each suited for specific environments.

Single-ply roofing systems consist of a single layer and are designed for low-slope roofs. Most low-slope roofs in the United States today have a single-ply roofing system installed. The three most popular types of single-ply membranes are TPO, EPDM, and PVC.

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Types of Single-Ply Membrane

TPO

TPO (Thermoplastic Polyolefin) is a highly flexible and durable membrane that’s comprised of various synthetic polymers and reinforcing scrim.

Like all single plies, TPO is manufactured into rolls of various widths and membrane thicknesses. It’s mostly white but also available in black, gray, and tan.

TPO membranes produce a highly reflective and UV-resistant roof surface which can significantly lower building energy costs. They also resist damage caused by impacts, moisture, and biological growth.

Despite being relatively new to the commercial roofing industry, TPO is the most prevalent single-ply material on the market today. With a price tag ranging from $3 to $9 per square foot, it’s also the least expensive.

A TPO roofing system’s life expectancy ranges from 10 to 25 years. This noticeably wide disparity is primarily due to material quality variations from one manufacturer to another.

Unfortunately, TPO membranes do not stand up well to excessive heat loads. The surplus of UV radiation causes their seams and flashings to separate and form membrane cracks.

EPDM

EPDM (Ethylene Propylene Diene Monomer), or EPDM rubber, consists of flexible synthetic rubber. It is typically used on low-slope roofs. EPDM has a price range of $4-$10 per square foot, putting it in between TPO and PVC in terms of cost. Also, EPDM is less durable than TPO and PVC membranes.

While EPDM is highly flexible, it is susceptible to damage from foot traffic and wind-driven debris. It also tends to have an unattractive appearance, especially as it ages.

EPDM is ideal for extreme climates with a temperature range of -40°F to 300°F. Additionally, EPDM is eco-friendly and long-lasting, with a lifespan of 10 to 25 years.

PVC

PVC (polyvinyl chloride) is a plastic single-ply membrane made using less oil and petroleum than TPO or EPDM. Unfortunately, PVC is typically more expensive than TPO and EPDM. The average cost of PVC roofing material is as high as $12 per square foot.

However, PVC makes up for its high cost in its strength, reflective properties, durable seams, ability to expand and contract, and longevity—ultimately creating a better investment for the building in the long run.

PVC also has reflective properties to keep the membrane cool (and eco-friendly) and protect it from discoloration and UV damage. These properties also make PVC resistant to moisture, chemicals, fire, and wind-driven debris.

PVC’s hardy, protective qualities culminate in its having the longest service life out of all the single-ply roofing membranes, equating to fewer repair costs over the years. PVC is estimated to last up to 30 years or more (compared to 10-25 years for TPO and EPDM).

Reflective vs. Retentive Membranes

Single-ply roofing material is manufactured in either black (retentive) or white (reflective) membrane. While custom colors are available, black and white are the standard.

White single-ply membranes TPO and PVC) are better at reflecting the sun’s UV rays, making them more suitable for warmer, sunnier climates. Ultimately, the superior reflectivity helps keep buildings cooler.

Black single-ply membranes (like EPDM) are retentive, which absorbs more of the sun’s heat. These membranes are better suited in cooler climates to retain heat in the building.

White vs black single-ply roofing energy efficiency illustration
Reflective vs. retentive single-ply membranes

In the commercial roofing industry, “cool roofs” are often pushed above any other type of roofing because they keep energy costs low, specifically cooling costs—but this only applies to roofs in warmer climates. If heating costs are high, a dark, heat-retentive roof may be the better fit. Certain environmental factors will determine which membrane is the best option.

Pros of Single-Ply Roofing

Easy to Install

Single-ply gets its name because it is installed in a single layer, meaning installation will take less time and labor than other (multi-layer) roofing systems. Single-ply is manufactured in large rolls, which are easy to install.

Cost Effective

The durability of single-ply means it requires fewer repairs. It has a long service life—making it worth every penny in the long run.

Lightweight

Its single layer makes single-ply lightweight compared to other types of multi-layer membranes.

Energy Efficient

Single-ply is available in light and dark colors, making it ideal for conserving or reflecting heat, depending on the climate.

Reliable

Most single-plies have been around for decades and are considered highly reliable among commercial roofing contractors.

Cons of Single-Ply Roofing

Punctures Easily

Unfortunately, consisting of only one layer has its drawbacks, too. Although single-ply is durable regarding reflectivity and flexibility, it tends to puncture easily from outside damage.

Vulnerable Seams

Except for PVC’s welded and watertight seams, TPO and EPDM single-ply membranes have potential weaknesses in their seams (which can lead to leaks).

UV Exposure

Though single-ply is very reflective (especially if installed in white), it only has one layer protecting the building from the sun’s UV rays.

Installation of Single-Ply Roofing

There are different methods for assembling the various types of single-ply roofing systems:

Fully-adhered

Fully adhered single-ply systems are glued directly to the insulation boards, which are secured to the metal deck below. The process requires more screws (fasteners) which would need to be addressed should the roof ever be given a roof coating system.

Mechanically Attached

Mechanically attached systems are the most common form of single-ply membranes due to their ease of installation and relatively low cost. The roofing membrane is rolled onto the insulation and screwed into the metal deck below. The seams are then fused using a heat welder or bonding adhesive (depending on the type of single-ply system installed).

Ballasted

Ballasted membranes are not anchored to the decking material but rather ballasted with a thick layer of gravel. It uses heavy stones (heavier at least than the gravel used in built-up roofs) that can withstand high winds and other harsh environmental factors. The installation process is simple due to its loose-laid nature.

Metal Retrofit

A metal retrofit involves the installation of new metal panels over an existing roof system. Insulation is typically installed between the old and new roof layers. Finally, a single-ply membrane is installed on top.

Insulation Choices for Single-Ply Roofing

Insulation traps any heat that makes it past the roofing membrane and prevents it from traveling into the building below. Insulation is vital for any roof as it serves as the layer of thermal resistance between the roofing membrane and the metal roof decking of the building. Thermal resistance is also known as R-value, and the higher the R-value, the better the insulator.

There are three primary types of roofing insulation:
  • Polyiso (Polyisocyanurate) is the most common type of insulation in commercial roofing. Its R-value is higher, but it typically costs more than other types of insulation board.
  • EPS (Expanded Polystyrene) has one of the highest R-values among foam insulation boards and is used in various building construction, including walls, ceilings, floors, building facades, etc.
  • XPS (Extruded Polystyrene) is recognized for its pink, blue, and green colors. It is a dense, lightweight, and semi-permeable foam material developed with superior water resistance.

Depending on the type of insulation, a cover board may be needed. A cover board is sometimes installed between the roofing membrane and the insulation layer. The cover board will depend on the type of insulation being installed. EPS and XPS require cover boards, but single-ply membranes can be applied to polyiso insulation without a cover board.

Conclusion

Single-ply is a reliable choice for many flat, low-slope roofing projects, having been around in the commercial roofing industry for decades. Ultimately, the specific type of single-ply membrane, as well as roofing insulation, will depend on factors such as cost, climate, energy needs, and any other particular requirements of the building owner or roofing contractor.

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EPDM PVC Single-Ply TPO