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RCI: Roof Consultants Institute

Re-cover (overlay): the installation of a new roof system over an existing system without removing an existing system.

Reinforced membrane: A roofing membrane that has been strengthened by adding polyester scrims or mats, glass fibers or other material.

Relative humidity: The amount of water vapor in the air compared to the amount of water vapor that the air can hold at a given temperature. For example, if the relative humidity is 50%, then the amount of water vapor in the air is half of what the air could actually hold at that temperature.

Re-roofing: the procedure of installing a new roof system.

Ridge: the line where two planes of roof intersect, forming the highest point on the roof that runs the entire length of the roof.

Ridge cap: material applied over the ridge or hip of a roof.

Roof assembly: an assembly of interacting roof components including the roof deck, vapor retarder (if present), insulation and roof covering.

Roof covering: the exterior roof cover or skin of the roof assembly, consisting of membrane, panels, sheets, shingles, tiles, etc.

Roof curb: raised frame used to mount mechanical units (such as air conditioning or exhaust fans), skylights etc. on a roof.

Roof slope: the angle a roof surface makes with the horizontal, expressed as a ratio of the units of vertical rise to the units of horizontal length (sometimes referred to as run). For English units of measurement, when dimensions are given in inches, slope may be expressed as a ration of rise to run such as 4:12 or as an angle.

Roof system: a system of interacting roof components, generally consisting of a membrane or primary roof covering and roof insulation (not including the roof deck) designed to weatherproof and, sometimes, to improve the building’s thermal resistance.

Rust blush: early stage of rust indicated by an orange or reddish color.