Going Behind The Scenes Of Commercial Roof Anatomy

How many facilities managers or property owners really know their roofs? A commercial roof’s profile, from the roof deck up through the top layer, can be complex. Damage to one of the layers can affect your roof’s performance and diminish its life. Knowing commercial roof anatomy, you can be proactive in preventing little problems from growing into nightmare scenarios. 

The Anatomy of a Commercial Roof

Common to All Roofing Systems

Some components of commercial roof anatomy are common across building types. Every low-slope roof (less than 3:12 pitch) needs a roof deck, whether wood, concrete, or steel. The commercial roof sits on and is fastened to the roof deck.

The roof needs a drainage system since no roof is waterproof — it is water resistant. Another key component is insulation, which is almost always rigid and tapered to provide some or all of the pitch to the roof. 

A reliable, local commercial roofing contractor will work with you to ensure the basics, structural support, drainage, and insulation, are in good shape before concentrating on the roofing system itself. 

Built-Up Roofing Systems

Built-up roofing (BUR) is probably the oldest roofing system any commercial property owner will encounter. Though over 100 years old, it is still a reliable, serviceable solution where economy is key. 

Layers of hot bitumen and felts (whether fiberglass-reinforced or organic) are built up through intense labor. The number of layers, or plies, determines the durability of the roof. You will hear a roofer discuss a three-ply BUR — or a four-ply BUR. 

Notice the roof system is all one type. Roofers do not introduce elaborate, differing layers with BUR. Vapor barrier, insulation, bitumen, felts, bitumen, felts, and so on until you get to the cap sheet and ballast. 

Modified Bitumen Roofing Systems

Modified bitumen, or Mod Bit, take the felts of BUR and modify them with polymers for added flexibility, strength, and longevity. Two principal types of Mod Bit are common today, based on the polymers added to the bitumen:

  1. APP (Atactic Polypropylene)APP increases the lifespan of the roof 
  2. SBS (Styrene Butadiene Styrene)SBS increases your roof’s flexibility and resistance to thermal shock, so it can expand and contract more easily 

These materials are reinforced with scrims, polyester mats, or fiberglass. Almost all Mod Bit roofs are two-ply or three-ply systems, which means you have fewer layers than a BUR roof, but with more advanced materials. 

Mod Bit roofs may be hot-mopped or torch-applied. Both BUR and Mod Bit are fast to install, easy to maintain, and definitely Old School commercial roof anatomy. You will see rolled materials laid down and then their seams sealed tightly together either through adhesives or heat. 

From the deck to the top cap sheet, you will see fewer layers with Mod Bit than with BUR, and the top will usually be a reflective surface. 

Single-Ply Roofing Systems

Single-ply roofing systems are the modern answer to Old School roofs. Sleek, expansive, highly durable, single-ply roofs reduce substantial noise, odor and time at installation. Almost all single-ply systems can be mechanically fastened, adhered using adhesives, or ballasted. 

Two principal types of single-ply systems are common in Florida:

  1. Thermosets — Thermosets are made from rubber polymers, with the most common being EPDM or Ethylene Propylene Diene Monomer
  2. Thermoplastics — Thermoplastics are made from polymers which soften when heated and harden when cooled, with polyvinyl chloride (PVC) and thermoplastic polyolefin (TPO) very common


Ethylene Propylene Diene Monomer (EPDM) are ideal single-ply solutions to Florida’s harsh sun. EPDM holds up very well to both sunlight and chemicals.

The typical profile of a commercial roof covered with EPDM is easier to understand than some commercial roof anatomy. From the top down:

  • EPDM Membrane
  • Adhesive
  • Insulation
  • Vapor Barrier
  • Roof Deck

It can get no simpler! Seams are either adhered with tape or liquid adhesives. An EPDM roof installs quickly, with minimal fuss and fumes. 


PVC roofing is seam-sealed with hot air. It performs very well in high heat conditions and has the same layering profile of other single-ply systems.

A typical PVC installation shows this commercial roof anatomy:

  • PVC Single-Ply Membrane
  • Roof Sheathing or Board
  • Mechanically Attached Insulation
  • Vapor Barrier
  • Roof Deck

PVC is an excellent choice in Florida because it is not well suited for cold weather. It becomes brittle in heat, but also reflects around 90 percent of solar exposure. 


Thermoplastic polyolefin (TPO) roof layers follow the same simple plan of EPDM roofs:

  • TPO Membrane
  • Adhesive
  • Insulation
  • Vapor Barrier
  • Roof Deck

In high-wind areas, TPO roofs are noted for their rugged, dependable service. They install easily and are economical. 

No Obligation Commercial Roofing Estimates in Miami and Fort Lauderdale

No matter the material that protects your commercial property’s roof, commercial roof anatomy means partnering with a knowledgeable, local roofer. Please call  A-1 Property Services today at 786-386-1149to find out how much we can tell you about your commercial roof. We offer a full menu of commercial roofing services in Miami-Dade and Broward counties, including inspections and maintenance plans, repairs, replacement and new installations. You may also contact us or request a commercial roofing estimate online.