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)

Insulation Contractors Association of America.


The International Conference of Building Officials.


The International Code Council.


The International Energy Conservation Code formerly known as the MEC. The IECC was published in 1998, 2000, 2003, 2006, and 2009.


Institute of Electrical and Electronics Engineers.


Illuminating Engineering Society of North America.


International Mechanical Code.

Incandescent Lamp

A lamp in which light is produced by a filament heated to incandescence by an electric current.

Indirectly Conditioned Space

An enclosed space within a building that is not a heated or cooled space, whose area-weighted heat transfer coefficient to heated or cooled spaces exceeds that to the outdoors or to unconditioned spaces; or through which air from heated or cooled spaces is transferred at a rate exceeding three air changes per hour. (Also see Heated Space, Cooled Space, and Unconditioned Space.)


The uncontrolled inward air leakage through cracks and interstices in any building element and around windows and doors of a building caused by the pressure effects of wind or the effect of differences in the indoor and outdoor air density or both.

Installed Interior Lighting Power

The power in watts of all permanently installed general, task, and furniture lighting systems and luminaires.

Insulated Sheathing

An insulating board having a minimum thermal resistance of R-2 of the core material.

Insulation R-Values

R-values are used to rate insulation and are a measurement of the insulation's resistance to heat flow. The higher the R-value, the better the insulation.

Integrated Part Load Value (IPLV)

A single-number figure of merit based on part-load EER, COP, or kW/ton expressing part-load efficiency for air-conditioning and heat pump equipment on the basis of weighted operation at various load capacities for the equipment.

Integrated-Control Economizers

Allows the cooling load of a building or space to be partially met by supplying outside air while the rest of the load is met by the refrigeration equipment within an HVAC system. Field- and factory-installed economizers supplied by major equipment manufacturers include integrated controls.

Interior Lighting Controls

Offer the ability for systems to be turned on and off either manually or automatically and include switches, time clocks, occupancy sensors, and other devices that regulate a lighting system.

Interior Lighting Power Allowance

The maximum lighting power in watts allowed for the interior of a building.

Interior Walls

Interior walls as defined by Section 802.2.9 are those walls not on the exterior of the building and that separate conditioned and unconditioned space.

International Foundation Class (IFC)

An object-oriented file format with a data model developed to facilitate interoperability in the building industry.

Isolation Devices

Devices that isolate HVAC zones so that they can be operated independently of one another. Isolation devices include, but are not limited to, separate systems, isolation dampers, and controls providing shutoff at terminal boxes.