Low-Slope Roofing Terms

Adhered – When a roof component is glued, bonded or sealed.

Architectural Metal Roof Systems – A metal roof system that has to be installed on a solid roof deck. It usually does not have watertight seams.

Ballast – Heavy materials used to hold a roof membrane in place.

Base Flashing – Strips of roof membrane installed in the vertical flashing area.

Base Sheet – A heavy felt that is used as the first ply in a BUR or modified bitumen system. It is usually coated.

Bitumen – Asphalt or coal tar.

Bonded – Glued or adhered.

Built-Up Roof (BUR) System – A membrane made of bitumen, felts and surfacing.

Cant – A triangular strip that creates a good angle for flashings.

Cold-rolled – When steel is applied into decking or roof panels at room temperature.

Cold-Applied Built-Up Roof (BUR) System – A built-up roof system that uses bituminous roof cement instead of hot asphalt.

Commercial Building – Public and industrial buildings. These buildings usually have low-slope roof systems.

Counterflashing – The metal flashing that shields the top edges and joints of the base flashing.

Crickets and Saddles – Raised areas built into a roof system. They help water flow to drains.

Drainage – A system that allows water to run off a roof.

Facer – A surfacing applied at the factory on some insulation boards.

Field – The open part of a roof.

Flashings – Components that make a watertight seal between the field of a roof and walls or penetrations.

Fully-Adhered – Installation method where a membrane is totally adhered.

Heat Welding –Heating materials with hot air or a propane torch so they will adhere.

Horizontal Flashing – Flashings that are installed around objects on the flat surface of a roof.

Insulation – Material that helps keep heat in a building in cold weather. It also helps keep heat out of a building in hot weather.

Loose-Laid and Ballasted – Installation method where a membrane is only attached in a few places. It is mostly held down by ballast.

Low-Slope Roof – A roof with a slope of three inches per foot or less.

Mechanically Attached – When material is attached to a deck with screws or other fasteners.

Mechanically Fastened – An installation method where a membrane is attached to a deck with fasteners.

Metal Roof System – A roof system made of metal panels.

Modified Bitumen – Bitumen that has been changed because polymers have been added to it.

Nailable – When parts of a roof system can be mechanically fastened to a deck.

Plies – Layers of felt.

Polymers – Chemical compounds. In modified bitumen roof systems, they are added to bitumen to change its chemistry.

Ponding – When water stays on a roof assembly. A roof system is supported by a deck.

Purlins – Metal channels or beams that support a structural metal roof system.

Re-Cover – Installing a new roof system on top of an existing roof system.

Reroofing – Installing a new roof system on a building that is not new.

Ribs – Grooves in steel panels that make them strong.

Roof Assembly – A roof deck, vapor retarder, insulation and roof membrane.

Roof Deck – The bottom part of a roof assembly. A roof system is supported by a deck.

Roof Membrane – The watertight part of a system.

Roof System – All the components above the deck.

Single-Ply Systems – Systems that have only one layer.

Slope – The incline of the roof.

Softening Point – The temperature at which asphalt or coal tar starts to melt.

Sprayed Polyurethane Foam-Based Roof System – A roof system that is sprayed in place.

Structural Metal Roof System – A metal roof system that does not need a solid deck. The seams are watertight.

Surfacing Types – Aggregate, cap-sheets or smooth-surfaced.

Tapered Insulation – Insulation that is made so the material has slope.

Tear-off – Removing an existing roof system.

Thermostats and Thermoplastics – Two types of single-ply membranes.

Underlayment – A material installed between a deck and roof system.

Valley – Area on a roof surface where two downward slopes meet.

Vapor Retarder – Material that helps keep a building’s moisture vapor from getting into the roof insulation.

Vertical Flashing – Flashings installed at upturned edges.