Racking—To stretch or strain by force, such as by the thermal or wind action.

RAD—Unit of absorbed dose of ionizing radiation equal to an energy of 100 ergs per gram of irradiated material. (See REM)

Radiation, types of:—Such as alpha particles, beta particles, gamma rays, X-rays, neutrons.

Radioactivity—Natural or artificial nuclear transformation. The energy of the process is emitted in the form of alpha, beta and gamma rays.

Rafter—One of a series of structural members designed to support roof loads. The rafters of a flat roof are sometimes called roof joists.

Raggle—Slot or groove cut in masonry to receive mortared-in flashing.

Rake—The sloped edge of a roof at the first or last rafter.

Rake angle—Angle fastened to purlins at rake for attachment of endwall panels.

Rake trim—A flashing designed to close the opening between the roof and endwall panels.

Raspberry—See Blueberry.

Real discount rate—The rate of interest reflecting that portion of the time value of money related to the real earning power of money over time.

Re-covering—The process of covering an existing roof system with a new roof.

Reentrant corner—An inside corner of a surface, where stress concentrations may occur.

Reference level—A reading or image associated with normal or dry conditions.

Reference temperature—A temperature of known value used as a basis to determine other temperatures.

Reglet—A groove in a wall or other surface adjoining a roof surface for the attachment of counterflashing.

Reinforced membrane—A roofing or waterproofing membrane reinforced with felts, mats, fabrics, or chopped fibers.

Reinforcement—A strong inert material bound into a plastic to improve its strength, stiffness, and impact resistance. Reinforcements are usually long fibers of glass, sisal, cotton, etc.—in woven or nonwoven form. To be effective, the reinforcing material must form a strong adhesive bond with the resin.

Relative humidity—The ratio of the mass per unit volume (or partial pressure) of water vapor in an air vapor mixture to the saturated mass per unit volume (or partial pressure) of the water vapor at the same temperature, expressed as a percentage.

Relative saturation—
Volume of water in sample x lOO
Maximum volume of water sample could hold

REM—Roentgen Equivalent Man—adjusts radiation measured in RAD to account for the differing effects on man.

Remedial roofing—The repair of selected, isolated portions of the roof system to return the roof to uniform condition. This normally involves the removal of wet materials along with correction of the original cause of the problem.

Reroofing—The removal of all roof system components down to the structural deck followed by installation of a completely new roofing system.

Resistance—The ratio of voltage to current in a direct current circuit.

Resistance, thermal—The average temperature difference between two defined surfaces of a particular body or assembly when unit thermal transmission in unit time through unit area is established between the surfaces. R=K«m2/W (R=°F«h«s«ft2/Btu).

Retrofit—the modification of an existing building or facility to include new systems or components.

Ridge—Highest point on the roof of the building which describes a horizontal line running the length of the building.

Ridge cap—A transition of the roofing materials along the ridge of a roof. Sometimes called ridge roll or ridge flashing.

Ridging—An upward, tenting displacement of a membrane, frequently over an insulation joint.

RIEI—The Roofing Industry Educational Institute. Rigid connection—See Moment connection.

Rigid frame—A structural frame consisting of members joined together with rigid (or moment) connections so as to render the frame stable with respect to imposed loads, without the need for bracing in its plane.

Rockwell hardness—A test for determining the hardness of the material based upon the depth of penetration of a specified penetrator into the specimen under certain arbitrarily fixed conditions of test.

Roentgen—Unit of quantity or dose for X-rays, gamma rays, etc. that will produce as a result of ionization one electrostatic unit of electricity in one cc of dry air.

Roll goods—A general term applied to rubber and plastic sheeting, usually furnished in rolls.

Roll roofing—Coated felts, either smooth or mineral surfaced.

Roof cement—See Flashing cement

Roof covering—The exposed exterior roof skin.

Roof curb—An accessory used to mount and level units (such as air conditioning and exhaust fans) on the sloped portion of the building roof.

Roof jack—An accessory used to cover pipes (such as vents or flues) that penetrate the roof panel.

Roof overhang—A roof extension beyond the endwall/sidewall of a building.

Roof seamer—Machine which crimps panels together or that welds laps of E/P systems using heat, solvent or dielectric energy.

Roof slope—The angle a roof surface makes with the horizontals, measured in the number of inches of vertical rise in a horizontal length of 12 inches. (Or as a ratio such as 1:48, or as a percent.)

Roofing system—An assembly of interacting components designed to weatherproof, and normally to insulate, a building's top surface.

Rubber—A material capable of quickly recovering from large deformations, normally insoluble in boiling solvent such as benzene, methyl ethyl ketone, and ethanol toluene azeotrope. A rubber in its modified state retracts within 1 min. to less than 1.5 times its original length after being stretched to twice its length.