A thick dictionary with the words “commercial roofing terminology” on the cover.

It can be hard to keep up with commercial roofing terminology if you aren’t part of the roofing industry. But, when it comes time to replace your roofing material (or you need to make repairs), it’s essential to know the meaning behind specific roofing terms.

We can help. Below, we break down all the terms – in their proper categories – so you can easily find what you need to know. Make sure your new roof is the right fit for you or that your existing roof is being taken care of in the right way.

Types of Roofing Systems


These are rarely used in commercial buildings but can be seen on occasion. They are common in residential buildings and feature an angled or pitched roof.


Also known as flat roofs, this term refers to roofs that have minimal to no slope. The majority of commercial and industrial buildings have this kind of roof.

Different Parts of Roofing Systems


A granular material made up of sand, gravel, stone or slag. Aggregate is used to make up the ballast in BUR and modified bitumen and can also be embedded in the top layer of the roofing membrane to add extra protection. Granules are a common type of aggregate that is embedded into asphalt roofing to provide UV protection.

Area Dividers

Used to separate large roof areas or systems that have incompatible materials or to assist in tapered insulation. Typically, area dividers are made of wood attached to a base plate.


Heavy materials placed on top of a low-slope roof that help secure roofing materials against wind uplift.

Base Ply

The bottom or first ply in modified bitumen roof systems under which additional plies are going to be installed.

Base Sheet

Asphalt-impregnated felt or fiberglass matting that is placed to enhance waterproofing and stability in some roof systems.

Butt Joint

A joint formed by neighboring sections of material.

Cap Sheet

Top layer of a multi-layered roofing system, particularly in built-up roofing (BUR) or modified bitumen systems.


A raised member that supports roof penetrations.


Vertical pipe that carries water runoff from a scupper or gutter to a lower level of the roof or to the ground.

Drip Edge

Installed under the underlayment or roofing felt. The drip edge of the roofing material overlaps the top of the drip edge to direct water away and prevent it from seeping under the roofing material into the roof deck.

End Lap

The overlap where one ply or panel extends beyond the end of the neighboring, underlying ply or panel.


Thin, weatherproof material that protects the vulnerable spots of your roofing system, such as the edges of skylights, HVAC systems or your roof’s edge.

Base Flashing

Installed at the base of walls, chimneys and other vertical surfaces to protect the joints where they meet with the roof.


A secondary layer of protection behind the primary flashing and above the base flashing to provide extra waterproofing to the edge of base flashing.


Devices like nails, staples, clips and bolts used to secure components of a roofing system together.


Installed below the roof deck to provide extra energy efficiency and keep the roofing system compliant with local building codes.

Lap Seam

The place where overlapping materials are sealed together.


Anything that penetrates the roof surface, such as pipes, skylights, vents and HVAC machines.

Roof Coating

A film applied to the roof surface to enhance weatherproofing.

Roof Covering

The outermost layer of a roofing system that protects against the elements – also known as the roofing material. There are several types of roofing materials, such as metal roof panels, EPDM, TPO and more.

Roof Deck

The base or substrate of the roof structure that supports the roofing material and coating. A roof deck can be made of different materials like plywood, oriented strand board (OSB), metal or concrete.


Opening in a wall, parapet wall or the roof edge that helps direct water runoff away from the building.

Structural Deck

The load-bearing roofing component that provides support for the roof as well as the floors below. The structural deck is typically made of steel or concrete and is part of the building’s overall structural system.


A depression around drains and scupper that helps direct drainage.


Top layer of a roof covering that is designed to protect underlying materials from the weather.


The roofing component that is installed directly onto the roof deck. It provides waterproofing for the interior of the building.

Vapor Retarder

A vapor barrier installed to slow the movement of water vapor throughout the roof assembly.

Roofing Installation Terms and Techniques

Air Blown Asphalt

A process for modified bitumen that involves blowing air through molten asphalt to produce a more durable final product.

Application Rate

The rate at which materials are applied per square foot.

Application Temperature

The temperature of a material when applied to the roof area.


The method of fastening roofing felt to the system so that the fasteners are covered by the ply.

Cure Time

The time needed for a material to reach its peak physical characteristics.


A process of roof assembly that treats the surface to increase its resistance against the passage of water.

Drying Time

Time required for the material to no longer be adversely affected by weather conditions like dew, rain or freezing.


The process of positioning felt, aggregate or fabric into hot bitumen or adhesive.

Expansion Joint

A structural feature placed between two components that allows for movement and expansion without risk of damage.


Heating the underside of a sheet or melting the underside of polymer-modified bitumen into a molten material for strong adhesion.


Joining layers of material together through adhesion.

Phased Application

Installation where roofers take two or more separate time periods or a series of days to complete the process.


Bonding overlapping materials together.


The process of removing old roofing materials and components in preparation for the installation of a new roof.


The method of sealing free edges of a roof membrane.

Types of Roofing Materials

Some types of roofing material, such as metal roofs, are self-explanatory. But if you aren’t a roofing contractor, some of the more technical names can be hard to understand. Here is an explanation of the most common types of commercial roofing materials.

Built-Up Roofing (BUR)

A type of asphalt roofing. BUR is made by layering bitumen sheets over the roof deck.

EPDM (Ethylene Propylene Diene Monomer)

Also known as thermoset roofing. EPDM is a type of rubber roofing made from synthetic elastomer. It’s known for its low cost and high energy efficiency.

Modified Bitumen Roofing

There are two kinds of modified bituminous materials – styrene butadiene styrene, which looks like rubber, and atactic polypropylene, a thermoplastic polymer that is heat-welded and has the appearance of asphalt. Modified bitumen is made up of layers of fiberglass or polyester fabric.

PVC (Polyvinyl Chloride)

A thermoplastic roofing membrane made from synthetic polymer materials. It is reinforced with polyester or fiberglass.

Single-Ply Roofing Membranes

Single-ply roofing membranes are a material that consists of one single layer of flexible, synthetic material. TPO, PVC, and EPDM are all single-ply roofing materials.

TPO (Thermoplastic Olefin/Polyolefin)

A rubber, single-ply roofing membrane made from a blend of polypropylene and ethylene-propylene.

How We Talk About Roofing Material Quality

Abrasion Resistance

The material’s ability to withstand being worn away due to contact with abrasive, moving surfaces, including foot traffic and equipment.


Refers to how well the material can accept quantities of liquid or gas.


The strength of the bond between two surfaces held together by chemical or mechanical means.

Compressive Strength

How well a material can resist compression loads.


Ability of a roof surface to shed its absorbed heat.


The material’s ability to conduct heat and resist heat transfer.

Low-Temperature Flexibility

The ability of different roofing materials to resist cracking in low temperatures.


The rate in which vapor passes through a material.


How flexible or bendable a material is.

Puncture Resistance

How well roofing materials resist penetration from foreign objects.


A material’s thermal resistance.


A roofing material’s ability to reflect sunlight instead of absorb it, which assists in energy efficiency.

Service Life

How long a roofing system lasts without the need for replacement.

Tear Resistance/ Tear Strength

The force required to tear a material.

Terms For Roofing Damage


When the surface of a built-up bitumen roof begins to crack. Alligatoring is given this name because the pattern of cracks tends to look like alligator skin.


Raised bubbles or pockets in the surface of your roofing material. Blistering is often a sign of moisture infiltration.


Deterioration that takes place in metal roofing panels after long-term exposure to moisture, oxygen and other pollutants.

Ice Dam

A ridge of ice that forms along the roof edge from snow unfreezing and refreezing.


Accumulation of standing water on low-slope roofs. Typically with ponding, you see shallow pools of water up to 48 hours after rainfall. Anything after 48 hours can indicate a problem with your roof.

Talk to the Experts

Now you have all the commercial roofing terminology you need to discuss your roofing project – which is a necessary step in making sure the job gets done right.

The most important thing, however, is to partner with a trusted, reliable commercial roofing contractor. Don’t worry – TEMA has your back. We’re here to educate and ensure the success of your commercial roof and your business.

If you need a roof replacement, a repair or a comprehensive system to monitor the health of multiple commercial roofing systems, talk with our experts. Reach out today to put us on your team.