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| R-Value | The measure of a material’s resistance to heat flow. The higher a material’s R-value, the more it insulates. |
| Racking | The method of installing asphalt shingles where the shingles are installed straight up to the ridge rather than horizontally. If this method is used with 3-tab shingles, the throats of every other course will line up. |
| Rafter | The structural member extending from the downslope perimeter of a roof to the ridge or hip and is designed to support the roof deck and roof system components. |
| Raggle | A groove that is cut into the side of a vertical surface such as a wall or chimney that is used to insert a flashing element such as a reglet or counterflashing. |
| Rake | The sloped perimeter edge of a roof that runs from the eaves to the ridge. The rake is usually perpendicular to the eaves and ridge. |
| Rake-Starter | A starter strip placed along rake edges for use in asphalt shingle roofing. See also Bleeder Strip. |
| RCI | Roof Consultants Institute |
| RCMA | Roof Coatings Manufacturers Association |
| RDCA | Roof Deck Contractors Association |
| Re-Cover (Overlay) | The installation of a new roof system over an existing system without removing an existing system. |
| Re-roofing | The procedure of installing a new roof system. |
| Reglet | A receiver, usually sheet metal, that counterflashings are attached to. Reglets can be surface-mounted, set in a raggle, or be part of the wall assembly. |
| 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 percent, then the amount of water vapor in the air is half of what the air could actually hold at that temperature. |
| Remove and Reinstall | To remove a component and reuse that component by reinstalling it. |
| Remove and Replace | To remove a component and replace it with a new component of the same or similar type. |
| Resin | The "B" component in SPF that is mixed with the "A" component in order to form polyurethane. Resin contains a catalyst, fire retardants, a blowing agent, Polyol, and a surface active agent. |
| 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. |
| Ridge Course | The final course of roofing applied that covers the area where two or more roof planes intersect. |
| Ridge Vent | An exhaust venting device located at the ridge of a roof that works in conjunction with a starter or under eave soffit vent and is used to ventilate attics. Ridge vents and their cooperative starter or soffit vents should be installed at a 1:1 ratio in order to function properly. |
| Ridging | The formation of a Buckle. |
| RIEI | Roofing Industry Educational Institute |
| RMA | Rubber Manufacturers Association |
| Roll Goods | The term used for all roofing materials that come in rolls. |
| Roof Assembly | A term used to describe all of the roof components including structural roof deck. |
| Roof Cement | See Asphalt Roof Cement and Coal Tar Roof Cement. |
| Roof Covering | The outermost reinforced layer of the roof assembly. In BUR it’s the multiple-ply membrane, in Thermoplastic roof systems it’s the thermoplastic sheet, etc. |
| Roof Curb | A frame used to structurally mount rooftop equipment such as HVAC units, exhaust fans, skylight, etc.; may be pre-constructed or constructed on site. |
| Roof Jack | (1) A steel bracket fastened to the roof that is used to support toe boards. <BR><BR>(2) A term used to describe a Pipe Boot or Flashing Collar. |
| Roof Overhang | That portion of the roof that extends beyond the exterior wall line of the building. |
| Roof Seamer | (1) A mechanical device used to crimp metal roof panels and make the seams watertight. <BR><BR>(2) A machine used to weld membrane laps of PVC (Thermoplastic) roofing material. |
| Roof Slope | The angle made by the roof surface plane with the horizontal plane and expressed as the amount of vertical rise for every twelve inch (12") horizontal run. For instance, a roof that rises four inches (4") for every twelve inch (12") horizontal run, is expressed as having a "four in twelve" slope; often written as "4:12." Expressed as a percentage, the slope would be 33%, which is equal to 4 divided by 12. Also known as the Pitch of a roof. |
| Roof System | Multiple roof components assembled to provide waterproofing (and sometimes insulating) capabilities for a structure. |
| Roofer | An individual who installs roof systems and materials. |
| Rosin | Non-asphaltic material used as slip sheets and sheathing paper in roof systems. Also referred to Rosin Paper and Rosin-Sized Sheathing Paper. |
| Run | The horizontal dimension of a slope. |
| Rust Blush | Early stage of rust indicated by an orange or reddish color. |