The following is a compilation of building energy-code related terms and acronyms used on the Building Energy Codes website and throughout the building construction industry.

Select a letter to navigate through the glossary:


A (23) B (23) C (41) D (27) E (28) F (15) G (12) H (21) I (20) K (5) L (11) M (16) N (15) O (11) P (21) R (22) S (37) T (14) U (12) V (11) W (10)

A measure (h ft2 °F/Btu) of thermal resistance, or how well a material or series of materials resists the flow of heat. The R-value is the reciprocal of the U-factor.

Radiant Heating System

A heating system that transfers heat to objects and surfaces within the heated space primarily (greater than 50%) by infrared radiation.

Raised Truss

Raised truss refers to any roof/ceiling construction that allows the insulation to achieve its full thickness over the plate line of exterior walls. Several constructions allow for this, including elevating the heel (sometimes referred to as an energy truss, raised-heel truss, or Arkansas truss), use of cantilevered or oversized trusses, lowering the ceiling joists, or framing with a raised rafter plate.

Rated Lamp Wattage

The power consumption of a lamp as published in manufacturers' literature.

Readily Accessible

Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to climb over or remove obstacles or resort to portable ladders, chairs, etc. In public facilities, accessibility may be limited to certified personnel through locking covers or by placing equipment in locked rooms.


The Rural Economic and Community Development, formerly the Farmer's Home Administration.

Recirculating System

A domestic or service hot water distribution system that includes a closed circulation circuit designed to maintain usage temperatures in hot water pipes near terminal devices (e.g., lavatory faucets, shower heads) to reduce the time required to obtain hot water when the terminal device valve is opened. The motive force for circulation is either natural (because of water density variations with temperature) or mechanical (recirculation pump).


Lowering the temperature of air that has been previously heated by a mechanical heating system.

Record Drawings

Drawings that record the conditions of the project as constructed. These include any refinements of the construction or bid documents.


The ratio of the light reflected by a surface to the light incident upon it.

Reflector Lamp

A class of incandescent lamps that have an internal reflector to direct the light. Reflector lamps are typically characterized by reflector shapes such as R (reflector), ER (elipsodial reflector), PAR (parabolic aluminized reflector), MR (multi-faceted reflector), and others.


Raising the temperature of air that has been previously cooled either by mechanical refrigeration or an economizer system.


Automatic adjustment of the controller set point to a higher or lower value.


Spaces in buildings used primarily for living and sleeping. Residential spaces include, but are not limited to, dwelling units, hotel/motel guest rooms, dormitories, nursing homes, patient rooms in hospitals, lodging houses, fraternity/sorority houses, hotels, prisons, and fire stations.

Residential Building, Group R-2

Residential occupancies containing more than two dwelling units where the occupants are primarily permanent in nature such as apartment houses, boarding houses (not transient), convents, monasteries, rectories, fraternities and sororities, dormitories and rooming houses. For the purpose of this code, reference to Group R-2 occupancies shall refer to buildings that are three stories or less in height above grade.

Residential Building, Group R-4

Residential occupancies shall include buildings arranged for occupancies as residential care/assisted living facilities including more than five, but not more than 16 occupants, excluding staff. For the purpose of this code, reference to Group R-4 occupancies shall refer to buildings that are three stories or less in height above grade.


The upper portion of the building envelope, including opaque areas and fenestration, that is horizontal or tilted at an angle of less than 60° from horizontal.

Roof Assembly

A roof assembly shall be considered to be all roof/ceiling components of the building envelope through which heat flows, thus creating a building transmission heat loss or gain, where such assembly is exposed to outdoor air and encloses conditioned space. The gross area of a roof assembly consists of the total interior surface of all roof/ceiling components, including opaque surfaces, dormer and bay window roofs, treyed ceilings, overhead portions of an interior stairway to an unconditioned attic, doors and hatches, glazing, and skylights exposed to conditioned space that are horizontal or sloped at an angle less than 60° from the horizontal.

Roofing With Insulation Entirely Above Deck

A roof with all insulation (1) installed above (outside of) the roof structure and (2) continuous (i.e., uninterrupted by framing members).

Room Air Conditioner

An encased assembly designed as a unit to be mounted in a window or through a wall, or as a console. It is meant to provide direct delivery of conditioned air to an enclosed space, room, or zone. It includes a prime source of refrigeration for cooling and dehumidification and a means for circulating and cleaning air. It may also include a means for ventilating and heating.

Room Cavity Ratio

A factor that characterizes room configuration as a ratio between the walls and ceiling and is based upon room dimensions.


Revolutions per minute.