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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.


One of the finished upright sides of a door or window frame.

Jamb Stud

Wood or metal stud adjacent to the door jamb.

Joint Compound

A plastic gypsum mixture used to cover the joints and fasteners in gypsum wallboard installations.


Forming control joints in a concrete slab.


Small beam that supports part of the floor, ceiling or roof of a building.

Joist Hanger

Metal shape formed for hanging on the main beam to provide support for the end of a joist.


A meter-kilogram-second unit of work or energy.


A coarse fiber obtained from two East Indian tiliaceous plants.

Keene's Cement

A hard, high-strength, white, quick-setting finishing plaster made from burnt gypsum and alum.


(1) A chamber with controlled humidity, temperature, and airflow in which lumber is dried.

(2) A low-pressure steam room in which green concrete units are cured.

Kiln-Dried Lumber

Lumber that has been dried and seasoned with carefully controlled heat in a kiln.

Kinetic Energy

The energy of a body with respect to the motion of the body.

Knitted Construction

Carpet formed by looping pile yarn, stitching, and backing together.

Label Service (UL)

Program allowing a manufacturer to place Underwriters Laboratories Inc. labels on his products that have met UL requirements. A UL representative visits the manufacturing location to obtain samples of the products for testing by UL. In some cases, samples are also purchased on the open market for testing. The public is thereby assured that products bearing the UL label continually meet UL specifications.


A fast-drying clear or pigmented coating that dries by solvent evaporation.


A material made by bonding several layers of material.

Laminate Wood

A product made by bonding layers of wood or other material to a wood substrate.

Laminated Glass

Glass panels that have outer layers of glass laminated to an inner layer of transparent plastic.

Laminated Veneer Lumber

A structural lumber manufactured from wood veneers so that the grain of all veneers runs parallel to the axis of the member.


A general term used to describe the source of artificial light. Often called a bulb or tube.

Landing Zone, Elevator

The area 18 inches (5490 mm) above or below the landing floor.

Latent Heat

Heat involved with the action of changing the state of a substance, such as changing water to steam.

Lateral Force

A force acting generally in a horizontal direction, such as wind against an exterior wall or soil pressure against a foundation wall.

Lateral Loads

Loads moving in a horizontal direction, such as the wind.


A water-based coating, such as styrene, butadiene, acrylic, and polyvinyl acetate.


The base material for the application of plaster.

Leaks (Sound)

Small openings at electrical boxes and plumbing, cracks around doors, loose-fitting trim and closures all create leaks that allow sound to pass through, reducing the acoustical isolation of a wall, floor or ceiling system.

Ledger Strip

Strip fastened to the bottom edge of a flush girder to help support the floor joists.

Leveling Plate

A steel plate set in grout on top of a concrete foundation to create a level bearing surface for the base of a steel column.

Life-Cycle Costing

Selection of the most economical material and systems based on initial costs, maintenance costs and operating costs for the life of the building.

Lift-Slab Construction

A method of building site-cast concrete buildings by casting all the floor and roof slabs in a stack on the ground and lifting them up the columns with a series of jacks and welding them in place.


A pane of glass.

Light-Gauge Steel Structural Members

Load-bearing members formed from light-gauge steel rolled into structural shapes.

Lighting Fixture

See luminaire.

Lighting Outlet

An electrical outlet to which a light fixture is connected.

Lightweight Steel Framing

Structural steel framing members made from cold-rolled lightweight sheet steel.


An amorphous substance that penetrates and surrounds the cellulose strands in wood, binding them together.


A white to gray powder produced by burning limestone, marble, coral, or shells.


A sedimentary rock consisting of calcium and magnesium.

Limiting Height

Maximum height for design and construction of a partition or wall without exceeding the structural capacity or allowable deflection under given design loads.


Horizontal member spanning an opening such as a window or door. Also referred to as a Header.

Liquid Limit

Related to soils, the water content expressed as a percentage of dry weight at which the soil will start to flow when tested by the shaking method.

Live Load

Part of the total load on structural members that is not a permenant part of the structure. May be variable, as in the case of loads contributed by the occupancy, and wind and snow loads.


Force provided by weight, external or environmental sources such as wind, water and temperature, or other sources of energy.


Carrying an imposed load.

Loomed Construction

Carpet formed by bonding the pile yarn to a rubber cushion.

Lot Area

Total horizontal area within the lot lines of a parcel of land.

Lot Line

The boundary line of a lot.


Subjective response to sound pressure, but not linearly related thereto. A sound with twice the pressure is not twice as loud. See Decibel.


Opening with slanted fins (to keep out rain and snow) used to ventilate attics, crawl spaces and wall openings.

Low-E Glass

A low-emissivity glass that has a thin metallic coating that selectively reflects ultraviolet and infrared wavelengths of the energy spectrum.

Low-Emissivity Coating

A surface coating used on glass that permits the passage of most shortwave electromagnetic radiation (light and heat) but reflects longer-wave radiation (heat).

Low-Slope Roofs

Roofs that are nearly flat.


A product produced by harvesting, sawing, drying, and processing wood.

Lumber Grader

A person who inspects each piece of lumber and assigns a grade to it.

Lumber, Boards

Lumber nominally less than 2 inches thick and 2 inches or more in width.

Lumber, Dimension

Lumber cut and dressed to standard sizes.

Lumber, Dressed Size

The size of lumber after it has been cut to size and the surfaces planed.

Lumber, Machine Stress-Rated

Lumber that has been mechanically tested to determine its stiffness and bending strength.

Lumber, Matched

Lumber that is edge dressed to make close tongue-and-groove edge joints.

Lumber, Nominal Size

The size of lumber after it has been sawn to size but has not been surfaced.

Lumber, Patterned

Lumber that is shaped to a pattern or to a molded form.

Lumber, Rough

Lumber that has not been surfaced but may be sawn, edged, and trimmed.

Lumber, Shiplapped

Lumber that is edge dressed to make a lapped joint.

Lumber, Shop and Factory

Lumber intended to be cut up and used in some manufacturing process.

Lumber, Structural

Lumber that is intended for use where allowable strength or stiffness of the piece is known.


A unit for measuring the flow of light energy.


A complete lighting unit consisting of one or more lamps plus elements needed to distribute light, hold and protect the lamps, and connect power to the lamps. Also called a lighting fixture.


the luminous intensity of a surface of a given area viewed from a given direction.

Luminance Meter

A photoelectric instrument used to measure luminance. Also called a light meter.


The emission of light not directly caused by incandescence.

Luminous Flux

The rate of flow of light energy through a surface, expressed in lumens.

Luminous Intensity

The force that generates visible light express by candela, lumens per steradian, or candlepower.

Luminous Transmittance

A measure of the capacity of a material to transmit incident light in relation to the total incident light striking it.

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