Low-slope Roofing Terms
Here is some common low-slope roofing terminology to help you better understand the roofing industry!
Whether you are trying to solve roof problems or just need routine roof maintenance, it is very helpful to understand the basic terms roofing contractors use. This allows you to find a roofer that is right for your job and to get all your roof questions answered.
A great place to start learning is with this video from AskARoofer expert and Cotney Consulting Group President John Kenney!
To start with the basics of roofing information, the term flat roof is actually a bit of a misnomer. When we say something is a flat roof, it actually refers to a low-slope roof, but never one that has no slope.
Even if we can't see it, every roof will have a slight slope. In general, low-slope roofs have a minimum slope of 1/4 inch vertical to 12 inch horizontal (¼ per foot rise). Roofers will refer to roofs that are up to 3:12 pitch as low-slope or flat.
In addition to these basics, there is a lot of information about roofing a low-slope structure out there! When you are looking for roof help, it is good to understand the following terms so you can have precise and effective conversation.
Asphalt: A black or brown petroleum-like material used in various roofing materials and systems.
Asphalt cement: An asphalt-based sealant material to seal and adhere to roofing materials and is used in new installations and roof repair projects.
Ballast: A material installed over a roof membrane to help protect or hold it in place. Ballasts can consist of aggregate or concrete pavers.
Base Ply: The primary ply of roofing material in a roof system. Usually, a single layer.
Base Sheet: An asphalt-impregnated or coated felt used as the first ply used in built-up and modified bitumen roof systems.
Blistering: Bubbles that appear when moisture or air is trapped beneath the roofing layers.
Built-up Roofs (BUR): A low-sloped roof that consists of multiple layers of asphalt and ply sheets.
Cap Sheet: A roofing membrane with a granule surface used as the top ply of BUR or modified roof systems.
Caulk: A sealant used to fill or seal a joint or gap to prevent leaks.
Coating: A monolithic, fully adhered, fluid-applied roofing membrane used to protect and extend the life of an installed roofing system.
Condensation: The process where water vapor becomes liquid.
Coping: Fabricated commonly from metal and used to cover the top of a wall to protect it from the elements.
Counterflashing: A material usually fabricated from metal and installed over rooftop base flashing systems.
Decking or substrate: The material that lays between the structural components of a roof (joists and trusses) that the insulation and the roofing system are installed over. Common material in commercial construction is steel, precast concrete panel, structural concrete, cementitious wood fiber, wood planking, plywood/OSB and poured gypsum.
Downspout or leader: A pipe for draining water from roof gutters or scuppers.
Drip edge: A trim metal piece is installed at the roof's edge
EPDM: A synthetic rubber single-ply roofing membrane (ethylene propylene diene terpolymer) used in low-slope applications.
Fasteners: Any type of screw, rivet or nail used to secure insulation, base sheets, metal panels, trim and flashing materials together or to the roof deck.
Flashing: A material that is installed around a roof penetration or along an edge to help keep moisture from entering the layers below. Found along the roof's perimeter or at penetrations, walls, expansion joints, valleys, drains and other vertical areas of a roofing system.
Insulation: A material that is used to help maintain the temperature in a building by reducing the flow of heat to and from that building.
Membrane: The roofing system covering that serves as the waterproofing material. It can be composed of one material, or several materials laminated together.
Mineral-surfaced roofing: A type of asphalt roll roofing that has a granule surface.
Modified bitumen: A rolled roofing membrane manufactured with polymer-modified asphalt and polyester or fiberglass reinforcement.
Mopping: When a roofer applies hot asphalt or coal tar using a hand mop or mechanical applicator.
Penetration: Any constructed item going through the roofing system that requires flashing.
Ply: The number of layers of roofing membrane.
Polyvinyl chloride (PVC): A single-ply roofing membrane made from a synthetic plastic polymer used in low-sloped roofing applications.
Ponding: Water that accumulates in low-lying areas on a roof.
Primer: A liquid or aerosol spray used to prepare concrete and metal surfaces for roofing systems or flashing installation.
SPF (sprayed polyurethane foam): A material sprayed as a liquid in multiple layers to expand into a foam, creating a solid layer across an existing roof.
Square: A roof area measurement equal to 100 square feet.
TPO: A thermoplastic polyolefin single-ply roofing membrane used in low-slope applications.
Vapor retarder: A vapor-resistant material or membrane that reduces the rate at which water vapor can move through a material installed in a separate layer during roofing installation.
Warranty: This is a legal document from the roofing manufacturer or contractor to cover any issues with your new roof. There are three main types:
- A standard manufacturer's warranty covers the products you purchase.
- An extended manufacturer's warranty covers contractor workmanship along with expanded coverage for the products.
- A workmanship warranty from the contractor covers the installation, usually for one or two years.
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