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Term Definition

The numerical value used to indicate the resistance to the flow of heat.


An enclosed channel designed to carry wires and cables.


Forcing out of plumb of structural components, usually by wind, seismic stress or thermal expansion or contraction.

Radiant Heat

Heat transferred by radiation.


Transfer of heat energy through space by wave motion. Although the radiant energy of heat is transmitted through space, no heat is present until this energy strikes and is absorbed by an object. Not all of the radiant heat energy is absorbed; some is reflected to travel in a new direction until it strikes another object. The amount reflected depends on the nature of the surface that the energy strikes. This fact explains the principle of insulating foil and other similar products that depend on reflection of radiant heat for their insulating value. Radiant heat travels in straight lines in all directions at about the speed of light. In radiant heating systems, heat is often radiated down from the ceiling. As it strikes objects in the room, some is absorbed and some reflected to other objects. The heat that is absorbed warms the object, which, in turn, warms the surrounding air by conduction. This warmed air sets up gentle convection currents that circulate throughout the room.


That member forming the slanting frame of a roof or top chord of a truss. Also known as hip, jack or valley rafter depending on its location and use.

Rafter Tail

That part of a rafter that extends beyond the wall plate -- the overhang.

Rainscrean Principle

The principle that states that wall cladding can be made watertight by placing wind-pressurized air chambers behind the joints, which reduces the air pressure differentials between the inside and outside that could cause water to move through the joints.


The board along the sloping edge of a gable.

Ready-Mix Concrete

Concrete mixed in a central plant and delivered to the site by truck.


Steel bar used to reinforce concrete.

Receptacel Outlet

An outlet box in which one or more receptacles are installed.


A device installed in an electrical outlet box to receive a plug to supply electric current to portable equipment.


(1) A process in which iron is separated from oxygen with which it is chemically mixed by smelting the ore in a blast furnace.

(2) In regard to aluminum, the electrolytic process used to separate molten aluminum from the alumina.


The ratio of the intensity of light reflected by a material to the intensity of the incident light.

Reflectance Coefficient

A measure stated as a percentage of the amount of light reflected off a surface.

Reflected Coated Glass

Glass having a thin layer of a metal or metal oxide deposited on the surface to reflect heat and light.

Reflected Heat

See Radiation.

Reflected Sound

Sound that has struck a surface and "bounced off." Sound reflects at the same angle as light reflects in a mirror; the angle of incidence equals the angle of reflection. Large curved surfaces tend to focus (concave) or diffuse (convex) the sound when reflected. However, when the radius of the reflecting surface is less than the wavelength of the sound, this does not hold true. Thus, a rough textured surface has little effect on diffusion of sound.

Reflective Insulation

Material that reflects and thus retards the flow of radiant heat. The most common type of reflective insulation is aluminum foil. The effectiveness of reflective barriers is diminished by the accumulation of dirt and by surface oxidation.


The relative ability of a surface to reflect sound or light.

Refractive Index

The ratio of the speed of light in a material to the speed of light in a vacuum.


Nonmetallic ceramic material used where high temperatures (above 270 degrees F) are present, such as in furnace linings.


The medium of heat transfer that absorbs heat by evaporating at low temperatures and pressure and giving up heat when it condenses at a higher temperature and pressure.

Reinforced Brick Masonry

Brick masonry construction that has steel reinforcing bars inserted to provide tensile strength.

Relative Humidity

The ratio of the amount of water vapor present in the air to that which the air would hold if saturated at the same temperature.

Remote Control Circuit

An electric circuit that controls any other circuit using a relay or other such device.


The property of a material whereby it gives up its stored energy when deforming force is removed.


The ability to regain the initial shape after being deformed.

Resilient Flooring

Finished flooring made from a resilient material, such as polyvinyl chloride or rubber.


A natural or synthetic material that is the main ingredient of paint and binds the ingredients together.

Resistance, Electric

The physical property of a conductor or electric-consuming device to resist the flow of electricity, reducing power and generating heat.

Retaining Wall

A wall that bears against soil or other material and resists lateral and other forces from the material being held in place.


An admixture used to slow the setting of concrete.

Return Air

Air removed from a space and vented or reconditioned by a furnace, air conditioner, or other apparatus.


Persistence of sound after the source stops. When one hears the 10th, 20th, 50th, 100th, etc., reflection of a sound, one hears reverberation.

Reverberation Time

Essentially the number of seconds it takes a loud sound to decay to inaudibility after the source stops. Strictly, the time required for a sound to decay 60 dB in level.


Peak of a roof where the roof surfaces meet at an angle. Also may refer to the framing member that runs along the ridge and supports the rafters.

Rigid Frame

A structural framework in which the beams and columns are rigidly connected (no hinged joints).


Measurement in height of an object; the amount it rises. The converse is "fall."


Vertical face of a step supporting the tread in a staircase.

Riser, Plumbing

A water supply running vertically through the building to supply water to the various branches and fixtures on each floor.


A metal fastener used to hold metal plates by passing through holes in each and having a head formed on the protruding end.

Rock Anchor

A post-tensioned cable or steel rod inserted into a hole drilled in rock and grouted in place.


A nonmetallic-sheathed electric cable of type NM or NMC.

Roof Drain

A drain on the roof to carry away water to a downspout.

Roof Planks

Precast gypsum concrete members used for decking roofs.

Room Cavity Ratio

A relationship between the height of a room, its perimeter, and the height of the work surface above the floor divided by the floor area.

Rough Framing

Structural elements of a building or the process of assembling elements to form a supporting structure where finish appearance is not critical.


Related to carpets, the number of tufts per inch.

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