Rabbet - A rectangular longitudinal groove cut in the corner edge of a board or plank.

Radiant Heating - A method of heating, usually consisting of a forced hot water system with pipes placed in the floor, wall, or ceiling; or with electrically heated panels.

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

Rafter, hip - A rafter that forms the intersection of an external roof angle.

Rafter, valley - A rafter that forms the intersection of an internal roof angle. The valley rafter is normally made of double 2-inch-thick members.

Rail - Cross members of panel doors or of a sash. Also the upper and lower members of a balustrade or staircase extending from one vertical support, such as a post, to another.

Rake - Trim members that run parallel to the roof slope and form the finish between the wall and a gable roof extension.

Reflective Insulation - Sheet material with one or both sun faces of comparatively low heat emissivity, such as aluminum foil. When used in building construction the surfaces face air spaces, reducing the radiation across the air space.

Reinforcing - Steel rods or metal fabric placed in concrete slabs, beams, or columns to increase their strength.

Relative Humidity - The amount of water vapor in the atmosphere, expressed as a percentage of the maximum quantity that could be present at a given temperature. (The actual amount of water vapor that can be held in space increases with the temperature.)

Resorcinol Glue - A glue that is high in both wet and dry strength and resistant to high temperatures. It is used for gluing lumber or assembly joints that must withstand severe service conditions.

Ribbon (Girt) - Normally a 1- by 4-inch board let into the studs horizontally to support ceiling or second-floor joists.

Ridge - The horizontal line at the junction of the top edges of two sloping roof surfaces.

Ridge Board - The board placed on edge at the ridge of the roof into which the upper ends of the rafters are fastened.

Rise - In stairs, the vertical height of a step or flight of stairs.

Riser - Each of the vertical boards closing the spaces between the treads of stairways.

Roll Roofing - Roofing material, composed of fiber and satin rated with asphalt, that is supplied in 36-inch wide rolls with 108 square feet of material. Weights are generally 45 to 90 pounds per roll.

Roof Sheathing - The boards or sheet material fastened to the roof rafters on which the shingle or other roof covering is laid.

Rubber-emulsion Paint - Paint, the vehicle of which consists of rubber or synthetic rubber dispersed in fine droplets in water.

Run - In stairs, the net width of a step or the horizontal distance covered by a flight of stairs.