R Value – The overall coefficient of thermal resistance of a building material or assembly.

Rabbet – A groove cut in the surface along the edge of a board, plank or other timber. The recess in a door frame to receive the door.

Rabbet Joint – A joint that is formed by the fitting together of two pieces of timber that have been rabbeted.

Radiant Heating – Defined under “Heating”.

Radiator – Defined under “Heating.

Radio Outlet – Defined under “Electrical Terms”.

Raft Foundation – A layer of concrete, usually reinforced, extending under the whole area of a building and projecting outside the line of its walls; normally used to provide a foundation in cases there the ground is unduly soft or the load to be carried is unduly heavy.

Rafter – One of the series of structural members of a roof usually of 2-inch nominal thickness designed to support roof loads, but not ceiling finish.

Rafter Types –

            Hip Rafter – The rafter which forms the hip of a roof.

Jack Rafter – A short rafter that spans from the wall plate to a hip rafter or from a valley rafter to the roof ridge.

Valley Rafter – The rafters that are located at the center of roof valleys to support the Jack rafters.

Rail – A piece of timber or metal extending from one post to another, as in fences, balustrades, staircases, etc. In framing and paneling the horizontal pieces are called rails, and the perpendicular stiles.

Rail Post – A newel post.

Rainwater Leader – A downpipe from a roof or gutter designed to carry water from roofs to a drain or to the ground surface.

Rake – An incline, as in a pitched roof. The end of a wall that slopes or rakes back; slope.

Random Bond – A type of masonry in which the masonry units are not laid in any regular pattern, but are laid as a hit-and-miss bond.

Receptacle (Electric) – A contact device installed in an outlet for the connection of a portable lamp or appliance by means of a plug and flexible cord.

Recess – An indentation in the line of a wall as an alcove.

Register – A device to regulate the discharge of warm from ducts to rooms.

Reinforced Concrete Construction – Defined under “Construction Types”.

Reinforcement, Ratio of – The ratio of the effective area of the reinforcement cut by a section of a beam or slab to the effective area of the concrete at that section; the ratio of the area of the longitudinal bars in a column to the total area within the protective envelope; the ratio of the volume of the spiral reinforcement to the total volume within the outer circumference of the spirals of a spirally reinforced column.

Reinforcing Steel – Steel bars used in concrete construction for giving added strength; such bars are of various sizes and shapes.

Relative Humidity – The percentage of the existing partial pressure of the water vapor in a space to the saturation pressure at the same temperature, for example, air containing one half the amount of moisture it is capable of holding has a relative humidity of 50%.

Rendering – The surface treatment of a concrete or masonry wall to improve its appearance or increase its resistance to water penetration.

Retaining Wall – Any wall erected to hold back or support a bank of earth; any wall subjected to lateral pressure other than wind pressure; also an enclosing wall built to resist the lateral pressure of internal loads.

Ribbon – A narrow board let into studs to support joints.

Ridge – The summit-line of a roof; the line on which the rafters meet.

Ridge Beam – A horizontal structural member usually 2 inches thick, supporting the upper ends of rafters

Ridge Board – A horizontal member usually ¾ inch thick, at the upper end of the rafters, to which these rafters are nailed.

Ridge Roof – Defined under “Roof Types”.

Rift Sawn – See “Quarter Sawn”.

Rings, Annual Growth – The growth layer put on in a single growth year and comprising spring wood and summer wood.

Ripping – The sawing of wood parallel to the grain.

Rip-Rap – Stones or other material placed on a slope to prevent erosion, or support the embankment.

Rise – The vertical height from end supports to ridge of a roof. The height of a step in a  staircase. The vertical distance from the center of span of an arch in the line of the springings to the center of the intrados.

Riser – The vertical board under the tread in stairs.

Roof Joist – See “Joists”.

Roof Types –

            Curb – A roof in which the slope is broken on two or more sides; so called because a horizontal curb is built at the plane where the slope changes.

            Deck – Having sloping sides below a flat deck on top.

            Flat – A roof which is flat or one which is pitched only enough to provide drainage.

            Flat-Pitch – A roof with only a moderately sloping surface.

            Gable – A ridge roof which terminates in a gable.

            Gambrel – A type of roof which has its slope broken by an obtuse angle, so that the lower slope is steeper than the upper slope.

            Hip – In general, a roof which has one or more hips, a roof which has four sloping sides that meet at four hips and a ridge.

            Lean-To – A roof which has a single sloping surface that is supported at the top by a wall that is higher than the roof.

            Mansard – A type of curb roof in which the pitch of the upper portion of a sloping side is slight and that of the lower portion steep. The lower portion is usually interrupted by dormer windows.

            Monitors – A type of gable roof commonly used on industrial buildings, which has a raised portion along the ridge with openings for light and/or air.

            Pavilion – A roof which in plan forms a figure of more than four straight sides.

            Pent – A roof other than a lean-to-roof, which has a single sloping surface.

            Pitched – A roof that has one or more sloping surfaces pitched at angles greater             than necessary for drainage.

            Polygonal – A roof which in plan forms a figure bounded by more than four straight lines.

            Pyramid – A hip roof which has four sloping surfaces, usually of equal pitch, that             meet at a peak. '

            Ridge – A roof with two opposite slopes meeting at the top, and with a gable at             either end.

            Shed – A roof with only one set of rafters, falling from a higher to a lower wall.

Room or Space, Habitable – A room or space intended primarily for human occupancy.

Rotary Cut Veneer – Veneer cut by revolving a log against a knife running the length of the log, set in such a manner as to cut off from the log a thin sheet of a definite thickness and continuous length.

Roughcast – A sort of external plastering in which small sharp stones are mixed, and when wet, is forcibly thrown or cast against the surface being coated.

Roughing-In – Defined under “Plumbing Terms”.

Rough Lumber – Defined under “Lumber”.

Rough Opening – An unfinished window or door opening.

Rubble – Masonry of rough, undressed stones. When only the roughest irregularities are knocked off, it is called scablled rubble, and when the stones in each course are rudely dressed to nearly a uniform height, it is called ranged rubble.

Run – The horizontal stringer measurement used in stair framing.

Running Bond – See “Stretching Bond”.