From Tar and Gravel to Thermoplastics: A Deep Dive into the History of Single-Ply Roofing Membranes

TPO and PVC membranes are both white types of Single-Ply roofing membrane, they can be hard to distinguish.

For decades, commercial buildings relied on traditional roofing systems like built-up roofing (BUR) to protect their interiors from the elements. These multi-layered systems, often involving hot tar and gravel & asphalt, were the industry standard. However, the need for lighter, more flexible, and potentially more sustainable solutions paved the way for the development of single-ply roofing membranes – a technology that has revolutionized the low-slope roofing market. Join us as we journey back in time to explore the fascinating history of these innovative roofing materials.

What Exactly is Single-Ply Roofing?

Before we delve into the past, let's clarify what constitutes a single-ply roofing membrane. Unlike BUR systems that consist of multiple layers of asphalt and reinforcing fabrics, single-ply membranes are exactly what their name suggests: single layers of flexible sheets. These sheets are typically made from synthetic polymers and are designed to provide a durable, waterproof barrier for commercial and industrial buildings with low or flat roofs. They come in various materials, each with its unique chemical composition, installation methods, and performance characteristics. The two main types you'll encounter today are:

• Thermoplastics: These membranes can be repeatedly softened by heating and hardened by cooling, allowing for heat-welded seams. Common thermoplastic options include Thermoplastic Polyolefin (TPO) and Polyvinyl Chloride (PVC).

• Thermosets: These membranes undergo a chemical change during their manufacturing process, resulting in a material that cannot be re-melted. The most prevalent thermoset membrane is Ethylene Propylene Diene Monomer (EPDM), often referred to as "rubber roofing."

The Early Days: A Shift from Traditional Methods

While single-ply roofing as we know it today emerged in the latter half of the 20th century, the underlying need for effective, low-slope waterproofing solutions has existed for much longer. Historically, low-slope roofs presented a unique challenge as they couldn't rely on gravity as effectively as pitched roofs to shed water.

The earliest low-slope roofing membranes were often based on coal tar, a byproduct of coal-gas production. By the late 1800s, asphalt, a byproduct of crude oil refining, was introduced. These materials were typically applied in multiple layers with reinforcing felt, leading to the development of built-up roofing (BUR) systems. BUR became the dominant choice for commercial roofing for many decades due to its proven track record and relative affordability at the time.

The Dawn of Single-Ply: Innovation in Europe

The story of single-ply roofing truly begins in Europe during the early 1960s. It was here that the first thermoplastic roof membranes were developed and installed. Polyvinyl Chloride (PVC) was one of the pioneering materials in this movement. In 1966, a German company named Trocal is credited with formulating and producing the first known PVC roofing membrane.

PVC's inherent resistance to water and its flexibility made it an appealing alternative to traditional systems. Its ease of installation under various weather conditions also contributed to its early adoption. Within a few years, PVC membranes gained significant traction across Europe, covering millions of square feet of commercial roofs. Single plies are lighter and more flexible, but the additional benefit is that as older more experienced roofers who handled BUR installation retired, Single-Ply offered an easier, less costly system to install. BURS are built in the field following specifications for plies, asphalt temperatures and the amount to be applied for each ply. Single plies can just be rolled out and seamed. It takes less skill and far less costly equipment. They can also be installed much quicker than BURs so the labor cost is greatly reduced.

Crossing the Atlantic: Single-Ply Arrives in North America

Almost a decade after its European debut, single-ply roofing began to surface in the United States in the early 1970s. Initially, many of the PVC membranes used in the US market were supplied by European manufacturers.

However, the landscape of commercial roofing was about to undergo a significant shift due to external factors. The oil embargo of 1973 had a profound impact on the construction industry, particularly on the availability and cost of high-quality roofing asphalt used in BUR systems. This crisis created an opportune moment for alternative roofing technologies like single-ply membranes to gain a foothold in the North American market.

The Rise of EPDM: A Resilient Alternative

Around the same time PVC was making its way to the US, Ethylene Propylene Diene Terpolymer (EPDM), a thermoset membrane, was also introduced in North America in the early 1960s. Often dubbed "rubber roofing," EPDM quickly gained popularity due to its excellent weathering capabilities, durability, and relatively simple installation. Its long service life contributed to its reputation as a dependable roofing solution.

Initially, EPDM membranes were available in thinner mil thicknesses. However, as the technology matured, manufacturers like introduced a reinforced EPDM sheet with an internal scrim in the mid-1980s, enhancing its toughness and resistance to punctures. Today, contractors can even opt for 90-mil EPDM membranes, offering twice the puncture resistance of the original 45-mil versions.

The Emergence of TPO: A Modern Thermoplastic Solution

The early 1990s saw the introduction of another key player in the single-ply market: Thermoplastic Polyolefin (TPO). While similar flexible polyolefin (FPO) membranes had been used in Europe since 1991, the TPO formulations developed for the US market differed significantly.

TPO membranes offered the benefits of thermoplastic materials, such as heat-weldable seams for enhanced water tightness, along with improved energy efficiency and resistance to UV radiation and chemical exposure. Its lighter color options also contributed to its appeal in terms of reducing the urban heat island effect.

Single-Ply Today: A Dominant Force

From its humble beginnings in Europe in the 1960s, single-ply roofing has grown to become a dominant force in the low-slope commercial roofing market in North America. Its long service life, dependability, ease of installation, and ongoing advancements in material science have made it a preferred choice for architects, building owners, and roofing contractors alike.

The journey of single-ply roofing is a testament to the continuous innovation in the construction industry. From the early PVC and EPDM membranes to the more recent advancements in TPO technology, these single-layer wonders have fundamentally changed the way we protect commercial buildings from the elements. As material science continues to evolve, we can only expect further advancements and refinements in the world of single-ply roofing, ensuring its continued role as a vital component of modern building design.