The History of Commercial Roofing
Every commercial roof on the market today is the result of a long series of problems and solutions. Builders have spent thousands of years looking for a roof that keeps water out, survives the weather, resists fire and lasts long enough to be worth the cost. The low-slope roofs covering most warehouses, offices, retail centers and factories today are a fairly recent answer to that old problem.
Knowing how commercial roofing developed helps owners and facility managers understand why their roof was built the way it was, why certain systems fail the way they do, and what their options are when it is time to repair or replace it.
Early Roofs: Thatch, Clay, Slate and Stone
The earliest roofs were made from whatever was close at hand: thatch, reeds, sod, wood and animal hides. Over time, builders turned to longer-lasting materials. Fired clay tiles were used in China and later across Greece and Rome, and slate and stone roofs became common in parts of Europe where those materials could be quarried.
These roofs were steep. Steep slopes shed water quickly, which was the only reliable way to keep a building dry before waterproof membranes existed. Flat roofs did exist in dry climates, often built from packed earth or clay, but they depended on low rainfall rather than on any true waterproofing layer.
The Industrial Era and the First Flat Roofs
The industrial age changed what buildings needed. Factories, mills, warehouses and railroad buildings grew wider and larger, and steep roofs over very large footprints were expensive and impractical. Builders needed a way to cover big, nearly flat areas and still keep water out.
The answer came from tar. In the 1800s, roofers in the United States began layering felt or paper with hot coal tar pitch and covering the top with gravel. This became known as the tar-and-gravel roof, and it is the ancestor of what the industry now calls built-up roofing.
Built-Up Roofing Becomes the Standard
Built-up roofing, often called BUR, uses several plies of reinforcing felt set in hot bitumen, with a surface of gravel or a coating on top. Each layer adds redundancy, so a small defect in one ply does not automatically become a leak. The gravel protects the bitumen from sunlight and foot traffic.
As asphalt refining grew in the late 1800s and early 1900s, asphalt joined coal tar as a common bitumen for these roofs. For much of the 20th century, built-up roofing was the default choice for commercial and industrial buildings across the country. Many older buildings still have built-up roofs, or have newer systems installed over them.
Steel Buildings and Metal Roofing
The 20th century also brought steel-frame and pre-engineered metal buildings. Metal roof panels were fast to install on warehouses, shops and agricultural buildings. Over time, standing seam metal roofs, with raised seams and concealed fasteners, became a durable option for low-slope and steep-slope commercial buildings alike.
Metal roofs are valued for their long service life and resistance to fire, but they bring their own concerns: fastener corrosion, seam movement from thermal expansion and the need for proper flashing at penetrations and edges.
New Materials: Modified Bitumen and Single-Ply Membranes
In the second half of the 20th century, roofing chemistry advanced quickly. Rising oil prices and labor costs in the 1970s pushed building owners to look for systems that were faster to install and less dependent on large crews working with hot kettles.
- Modified bitumen: Asphalt blended with polymers such as SBS or APP for better flexibility and durability. Developed in Europe and adopted widely in the United States starting in the 1970s.
- EPDM: A synthetic rubber membrane that became one of the most common single-ply roofs in the country.
- PVC: A thermoplastic membrane with heat-welded seams, known for chemical and grease resistance, which made it popular on restaurants and industrial buildings.
- TPO: A thermoplastic membrane introduced in the United States in the 1990s that grew into one of the most widely installed commercial roofing systems.
Single-ply systems changed how commercial roofs were built. Instead of multiple layers built on site, a single factory-made sheet could cover large areas quickly, with seams that were glued, taped or heat-welded.
Spray Foam and Roof Coatings
Spray polyurethane foam roofing came into use in the 1960s and 1970s. Foam is sprayed as a liquid that expands and hardens into a seamless, insulating layer, then protected with a coating that blocks sunlight. It is especially common in hot, dry regions of the Southwest.
Liquid-applied coatings also grew into their own category. Acrylic, silicone and urethane coatings are now used to restore aging roofs, extend service life and add a reflective surface without a full tear-off, when the existing roof is still in suitable condition.
Energy, Codes and the Cool Roof Movement
As energy costs rose and building codes grew stricter, the roof became part of the building’s energy system rather than just a cover. Insulation levels increased, and in the late 1990s, programs to rate and label reflective roofing products helped launch what is now called the cool roof movement.
Cool roofs reflect more sunlight and absorb less heat, which can lower cooling loads and roof temperatures. Many jurisdictions now include roof reflectivity or insulation requirements in their energy codes, especially for low-slope commercial roofs in warm climates.
Building codes, fire ratings and wind uplift testing also shaped modern roofing. Insurers and testing laboratories developed standards for how roofs resist fire, hail and wind, and those standards now influence which systems are allowed on a given building.
Commercial Roofing Today
Today, commercial building owners can choose from more roofing systems than at any time in history. The right choice depends on the building, the climate, the budget, the roof’s traffic and equipment, and how long the owner plans to hold the property.
- Built-up and modified bitumen roofs for redundancy and toughness
- TPO, PVC and EPDM single-ply membranes for speed and value
- Standing seam metal for long service life
- Spray foam and coatings for seamless, insulated and restorable roofs
- Reflective surfaces and higher insulation to meet energy goals
What has not changed is the basic goal. A commercial roof has to keep water out, protect the people and equipment below it and deliver a reasonable service life for the money. The history of commercial roofing is really the history of finding better ways to meet that goal.
Planning a project? Learn more about the commercial roof life cycle or explore our commercial roof replacement services.