Glossary of Commercial Roofing Terms

Every industry has its share of phrases, jargon and or keywords that industry insiders bandy about without hesitation. To the uninitiated, these words can sound unfamiliar and somewhat odd; what do crickets, for example, have to do with membrane roofs?

As we believe an educated consumer is also the best customer, here are definitions of some of the most commonly used terms here at Quality Roofing Services and across the commercial roofing industry.

Roll your curser over any term which you’d like to learn more about and click when it changes color.

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a roofing materials ability to resist being worn away by contact with another abrasive surface, such as foot traffic, mechanical equipment, tree-limbs or branches, wind-blown particles, etc.

Frequently in commercial roofing, two types of roofing materials need to be stuck together or adhered to each other. Single-ply membranes and insulations use contact cement manually or spray applied.

This term refers to granular mineral-based material, aka stone, rock, and/or gravel that’s been crushed or broken down into small pieces. In the commercial roofing industry, aggregate is used as a surfacing material or ballast (see next definition) for certain roof systems.

A cementitious material composed primarily of bitumens found in a natural state or, more commonly, left as a residue after processing crude oil or petroleum. The material is used in roofing shingles as well as in Built-up Roofing systems and repair materials.

Ballast materials (like precast concrete or aggregate) use gravity to hold a single-ply roofing system in place.

A raised portion of a caused by either internal pressure, such as an enclosed pocket of air or the separation of a layer or membrane from a substrate; typically caused by water absorption and subsequent swelling or subsurface corrosion.

a roofing system with layers of different materials to achieve durability and waterproofness. BUR is a continuous and semi-flexible membrane that consists of felt or fabric layers (called plies) alternated with layers of other materials like tar/bitumen and aggregate. Often seen on older commercial buildings with low-slope roofs, BUR has been in use for 120 years. This type of roofing is no longer used in this area.

A metal cover or shield protecting the upper edges of the membrane base flashing or wall flashing; flashing which covers the top of buildings components, such as parapets or columns.

A roof system made of highly reflective and emissive materials for its top layer. When exposed to solar rays, cool roof surfaces remain at lower temperatures than roof surfaces made from non-reflective roofing products.

Cover board is used as an additional insulation board in certain roofing systems, such as single-ply membrane systems, where a high density impact resistant barrier is needed between the thermal insulation and the membrane. It is a substrate (see definition below) to which a membrane is fastened or adhered, but it also offers strong protection against destructive forces like hail, the installation of Solar Panels, heavily trafficked access areas and equipment maintenance traffic.

Despite their name, commercial flat roofs are not actually designed completely flat; these roofs are built with a slight pitch to keep water from ponding and move it toward the roof drainage system. A Cricket is a ridge structure designed to divert water on a roof around a structure (chimney, hvac unit or skylight for example) or from one roof area to another and directly to the roof drains.

A raised object used to support roof penetrations, such as skylights, heating or cooling equipment, hatches, etc., above the level of the roof surface.

A key structural component of a commercial buildings roof which supports the weight of the roof system, roof-top systems, additional loads as required by building codes and provides the substrate to which the roof is adhered.

A vertical pipe or conduit which carries runoff water from a scupper, conductor head or gutter to a lower roof level or to the ground or storm water runoff system.

A metal flashing with an outward projecting lower edge to control the direction of dripping water and help protect underlying building components.

Think of the term “elastic.” Elastomer is a material that can rapidly return to its original shape and dimensions after being stretched.

EPDM is an abbreviation for the chemical name of the single-ply rubber material used in many flat-roofed commercial buildings today — Ethylene Propylene Diene Monomer. EPDM roofing systems may also be called Thermoset systems, and these roofs are durable, versatile, and easy to install compared to many others. The term “Thermoset” means that the material cannot be reshaped by heating, and so it is resistant to thermal stress (defined below).

A structural separation between two building or construction elements to allow movement of the elements without damage to each element.

In the roofing world, exposure refers to the portion of the membrane that is not overlapped by a ply or course next to it. That is, the top layer of roofing material exposed to the elements after being installed is said to be the exposure.

Flashing are materials used to seal the edges of a roofing system. Flashing can be used around the perimeter, around penetrations, against walls, on expansion joints and to strengthen valleys and drains. Flashing should be used anywhere the roofing materials are interrupted or terminated.

When two layers of material must be bonded together (like sections of polymer modified bitumen or thermoplastics), heat in the form of hot air or flame plus pressure are used to fuse the two layers together.

Roof installation technique where the underside of a membrane sheet is heated with a propane torch or other heating device, melting the polymer-modified bitumen on the bottom side for adherence.

These letters stand for Heating, Ventilation, and Air Conditioning. What does that have to do with roofing? Because this equipment is often located on the roofs of commercial buildings, roofers have to work around it. Leaks can often form around places where HVAC equipment is installed, as well, since it connects to system components inside the building through the roof’s structure.

This is the name for ice formations at the transition between warm and cold roof surfaces. Ice dams form when previously melted snow and ice refreezes during winter. Ice dams need to be prevented, as they commonly back up under roofing materials, which leads to leaks inside your building.

Many roofers use an infrared camera to measure temperature differences in the roofing material. Significantly warmer spots may indicate the presence of moisture trapped in the roofing materials or in insulation.

Every roof requires some type of insulating material. The purpose is to keep the heat in during the winter and the cool in during the summer. A good insulating material can help reduce heating and cooling costs.

Live loads are generally moving and/or environmental (e.g., people, installation equipment, snow, ice, rain).

Generally waterproof membrane roof systems installed on slopes at or less than 3:12.

Membrane is a flexible or semi-flexible material that acts as a waterproofing component in the layers of roofing material. A membrane may be made of a single material or of several materials laminated together.

Mil is a unit of measurement. One mil is equal to 0.001 inches and is often used to indicate the thickness of a roofing membrane.

This is a part of a perimeter wall next to and extending above the roof.

A penetration can refer to any break in the roofing materials, such as a vent stack, skylight, HVAC and more.

Ponding refers to an excess amount of water gathering and standing in low lying areas of a roof. Generally, ponding describes water that remains on the roof 48 hours after precipitation in conditions conducive to evaporation.

Ponding refers to an excess amount of water gathering and standing in low lying areas of a roof. Generally, ponding describes water which remains on the roof 48 hours after precipitation in conditions conducive to evaporation.

This refers to a roof that has been purposefully designed to add additional roof slope to ensure proper drainage of the roof area within 48 hours of a rainfall. Positive drainage on all roofing systems is required by the building code.

This term refers to the act of getting more useful life from your commercial building’s roof by being proactive in caring for it to prevent problems. Here at Quality Roofing, we offer customized maintenance plans to suit your budget and keep your roof in great condition.

If you’ve ever shopped for insulation for your home or commercial building, you’ve heard this term, and you know that the higher the R-Value number, the better. This is because the term refers to thermal resistance, or the measure of a material’s resistance to heat flow. In practical application, R-Value denotes the specific thickness of an insulating material or construction type.

Roof slope refers to the angle the roof makes versus a horizontal surface. It may be expressed as a ratio of rise to run. 

The interacting components of a commercial roof consisting of a membrane or primary roof covering, roof insulation (not including the roof deck) and other components designed to insulate and weatherproof the building.

Especially with large commercial roofs, the roofing materials cannot all be installed in one big sheet, so there will be seams where sheets or types of material overlap. Seams are one of the most common places for leaks to happen.

Roofing membranes that are applied in one layer only are known as single-ply membranes. The EPDM systems we talked about above, as well as thermoplastic TPO and PVC systems (defined below), are commonly single-ply membranes.

Square refers to 100 square feet of roofing area.

Substrate refers to the surface upon which roofing materials or waterproof membranes are applied. The term may refer to the structural deck of the roof, underlayment, or a cover board (as defined above), depending upon the roofing system used.

An intentional depression around a roof drain or scupper which facilitates water drainage.

The decrease/ increase in the dimension or volume of a body because of temperature variations.

Underlayment is an asphalt-saturated felt or other sheet material installed between the roof deck and the roofing system. It is most often used in steep-slope roof construction. It is used to separate the roofing material from the deck, to shed water or to provide secondary weather protection in areas with extreme weather conditions.

Damage done to a roofing system by the ultraviolet rays of the sun.

This is a material installed to prevent water vapor from passing from the building environment into the layers of roofing materials.

It may sound strange, but all buildings need to “breathe” and exchange indoor and outdoor air. Roof vents are openings or devices that permit air to exit an enclosed structure. These vents must allow air and vapors to escape, but must not allow moisture to infiltrate the structure.

heavy duty roof protection padding used in high traffic and high-service-frequency areas on a rooftop, particularly those leading and adjacent to vents, hatches, and heavy-duty air-conditioning units to protect the primary roof surface from damage resulting from rooftop traffic or equipment maintenance.

In short, water infiltration equals roof leaks. If water or moisture is infiltrating, or getting into, your commercial building, you may have a major problem on your roof that requires attention right away.

The ability of a membrane, membrane material or other roof components to prevent water entry. Treatment of a surface or structure to retard the passage of water under hydrostatic pressure.

Wind is usually deflected away from the structure at the roof’s edges and peaks. With severe winds, this causes a drop in air pressure above the roof’s surface. This may cause membranes and roof edges to balloon or pull away from the decking.



If there is a roofing term you’d like to know more about, please contact us. If you’d like to learn more about commercial membrane roof replacement, commercial flat roof maintenance and repair or if you’d like to request an estimate, please fill out our Request an Estimate form.