A Glossary of Commercial Roof Terminology

A Glossary of Commercial Roof Terminology

Every industry has its special terms and odd phrases. Roofing is no different. These are some essential concepts you may need to know when conversing with your local roofer. 


Architecturally, all roofs are either low-slope roofs or steep-slope roofs. The pitch or slope (rise over run) determines the safe working environment for roofers, maintenance crews, third-party vendors and others. 

Low-slope roofs are pitched 3:12 or less, down to 0.25:12 (dropping only 1/4-inch in 12 inches). They are almost always roofed with single-ply membrane, built-up roofing (BUR), or modified bitumen. 

Steep-slope roofs are pitched greater than 3:12. These prominent roofs are often part of a commercial property to provide a “homey” appearance, shed massive amounts of snow, ice or water, or to provide advertising space. They are often roofed using fiberglass-asphalt shingles, tile, or metal roofing panels. 

Any projection through your roof is a penetration, like a sanitary stack, HVAC unit, electrical lines, and so on. The holes for these penetrations have to be sealed using either boots (most pipes) or curbs (HVAC units in particular). 


Commercial roofs are generally made from either membrane or layers:

  1. TPO — Thermoplastic Polyolefin, a single-ply reflective roof membrane noted for its good economy
  2. EPDM — A rubber membrane, ethylene propylene diene terpolymer, that is extremely economical
  3. PVC — Polyvinyl Chloride, a durable, heat-welded membrane
  4. Modified Bitumen — Plasticizers are added to bitumen to increase flexibility and age resistance:
    1. SBS, styrene-butadiene-styrene
    2. APP, Atactic polypropylene 
  5. BUR — Built Up Roofing is one of the oldest and least expensive roofing methods still around; it is a “tar and gravel” layered roof finished with ballast


Commercial roofs are installed with various methods. Seams are almost always either heat-sealed or solvent-sealed. In addition, mechanical fasteners can be used to adhere roofing materials to the steel (or wood) roof deck or to other layers of the roofing. 

Unitized roofing refers to shingles, metal panels, and tiles. These small units are individually adhered to slowly build up a roof expanse. This contrasts with membranes, which are rolled out (often in pieces nearly as big as the roof) and are adhered piece by piece along their seams. 

Whatever roofing system your building uses, our company is ready and waiting to help. Contact RoofTek® Roofing Solutions online, or by calling 1-833-ROOF-TEK today. We can dispatch roofing experts to assess your roof, document problems, and plan solutions.  

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