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Term Definition
I Joist

A wood joist made of an assembly of laminated veneer wood top and bottom flanges and a web of plywood or oriented strandboard.


International Conference of Building Officials, a nonprofit organization that publishes the Uniform Building Code.

Igneous Rock

Rock formed by the solidification of molten material to a solid state.


The density of luminous power in lumens per a specified area.

Impact Insulation Class

An index of the extent to which a floor assembly transmits impact noise from a room above to the room below.

Impact Insulation Class (IIC)

Single-number rating used to compare and evaluate the performance of floor-ceiling constructions in isolating impact noise. The advantages of this rating system are positive values and the correlation with Sound Transmission Class (STC) values -- both providing approximately equal isolation at a particular value. The IIC rating is used by building agencies for specifying minimum sound-control performance of assemblies in residential construction.

Impact Noise

Sound generated by impact on the floor or other parts of a building that is carried through the building.

Impact Noise Rating (INR)

Obsolete rating system for floor-ceiling construction in isolating impact noise. INR ratings can be converted to approximate IIC ratings by adding 51 points; however, a variation of 1 or 2 points may occur.

Impact Strength

The energy required to fracture a specimen when struck with a rapidly applied load.

Impact Test

A test for determining the resistance of a specimen fracture from a high-velocity blow.

In Situ

Undisturbed soil.


The emission of visible light produced by heating.


See Noncombustible.

Independent Footings

Footings supporting a single structural element, such as a column.


The process by which water soaks into the ground. Also called Percolation.


A mass of molten metal cast in a mold and solidified to be stored until used for forging or rolling into a finished product.


The amount of solar radiation on a given plane or surface.

Insulatig Glass

A glazing unit used to reduce the transfer of heat through a glazed opening by leaving an air space between layers of glass.

Insulation (Thermal)

Any material that measurably retards heat transfer. There is wide variation in the insulating value of different materials. A material having a low density (weight/volume) will usually be a good thermal insulator.

Insulation, Electric

A material that is a poor conductor of electricty.


A trapping device designed to collect materials that will not be able to be handled by a sewage treatment plant, such as grease, glass or metal chips, and hair.


To estimate untested values that fall between tested values.


The swelling of a fire-retardant coating when heated, which forms a low-density film that provides some resistance to the spread of flame on the surface.

Invert Elevation

The elevation of the bottom (flow line) of a pipe.


A metallic element existing in the crust of the earth from which ferrous alloys, such as cast iron, are made.


International Standards Organization, an organization similar in nature.

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