Knowing these basic roofing terms can help you make better decisions on roof maintenance

by Brianna Crandall — April 30, 2021 — Knowing basic roofing terms can help facilities managers (FMs) better evaluate proposals, talk to contractors, and communicate with owners. The roofing experts at Western Specialty Contractors, a St. Louis, MO-based specialty contractor in masonry and concrete restoration, waterproofing and specialty roofing, have provided some of the most common roofing terms and their definitions below to help FMs make more comprehensive decisions regarding their roof maintenance.


Blistering is a buildup of water vapor or gases that form a bubble underneath a roofing material’s surface. Typically occurring in built-up and modified bitumen roofs, blistering generally does not pose a problem unless it is stepped on or popped, then measures should be taken immediately to repair the opening.

If a blister is identified on a roof, FMs should leave it alone and not try to fix it. If the bubble is accidentally popped, FMs should take precautionary measures by covering the hole with duct tape until a specialty contractor with roofing experience can get out there and assess the situation.


Tenting is most common in EPDM or TPO roofs. Tenting occurs when adhesives break down or when not enough adhesive was used, and the material is starting to peel away in the form of a triangle, similar to the side of a tent. Tenting may also occur around curb flashing on HVAC units.

Once tenting occurs, the roofing system is breached and subject to water penetration. FMs should contact their roofing specialty contractor immediately when tenting occurs to ensure that repairs are made according to the manufacturer’s guidelines.


Similar to the cracks seen on a neglected, aged asphalt parking lot, alligatoring on a roof has a similar cracking and splitting appearance like an alligator’s skin. Alligatoring is caused by the sun drawing out and drying volatile oils within the roofing materials. This type of oxidation is a sure sign of an aged and damaged roof.


Ponding occurs when roof drains are clogged and water, leaves, and twigs collect on the roof like a small pond. Ponding can cause serious structural issues, as water can weigh more than eight pounds per square foot. Ponding is particularly damaging to modified bitumen and built-up roofing systems that have multiple seams for water and sediment to penetrate and cause damage.

Core sampling

Roofing contractors will take a core sample to determine how many layers and what types of roofing systems are on a roof. A 12-inch by 12-inch piece of roof, or a round core, is cut out down to the roof deck and pulled out to identify the various roofing materials used and their thicknesses.

If there are more than two roofs identified, building codes require that the entire roof be replaced. A core sample can indicate a roof’s age, thickness, composition, and whether it has been penetrated by water.


Flashing describes the vertical parts of a roof and can include curb and wall flashing. Flashing helps to divert standing or wind-driven water or snow from penetrating a joint in the roof, such as around chimneys, vent pipes, and walls.


Wrinkling is similar to blistering. It is simply a fold in the roofing system material caused by age, high winds or movement of the building. As in the bottom of an above-ground pool, a wrinkle may occur in the flooring material, but the pool is still able to hold water.

A wrinkle in the roofing material is an aesthetic concern and does not necessarily indicate that there is any water penetration or that a repair is necessary.


Splits are advanced openings and generally occur on an aged built-up roof where the oils have dissipated and dried to form a large crack. Splits can also occur in seams as the result of an application error. Splits should be repaired immediately as they are subject to damaging water penetration.

For more information on roof maintenance and Western Specialty Contractors services, visit the company’s website. Family-owned and -operated for more than 100 years, Western offers a nationwide network to help building owners, engineers, architects and property managers develop cost-effective, corrective measures that can add years of useful life to a variety of structures including industrial, commercial, healthcare, historic, educational and government buildings, parking structures and sports stadiums.