I-Joist: Manufactured structural building component resembling the letter "I." Used as floor joists and rafters. I-joists include two key parts: flanges and webs. The flange of the I joist may be made of laminated veneer lumber or dimensional lumber, usually formed into a 1 ½" width. The web or center of the I-joist is commonly made of plywood or oriented strand board (OSB). Large holes can be cut in the web to accommodate duct work and plumbing waste lines. I-joists are available in lengths up to 60 feet long.

ID (Inside Diameter): The diameter measurement taken from the inside of a pipe. A common method for sizing pipe.

IIC: A new system utilized in the Federal Housing Administration recommended criteria for impact sound insulation.

Incandescent Lamp: A lamp employing an electrically charged metal filament that glows at white heat. A typical light bulb.

Incompatibility: Descriptive of two or more materials which are not suitable to be used together.

Indemnification Clause: Provision in a contract in which one party agrees to be financially responsible for specified types of damages, claims, or losses.

Index: The interest rate or adjustment standard that determines the changes in monthly payments for an adjustable rate loan.

Infiltration: The process by which air leaks into a building. To find the infiltration heating load factor (HLF), the formula to account for the extra BTUs needed to heat the infiltrated air is BTU/HR = building volume x air changes x BTU/cu.ft/hr x TD (temperature difference).

Inlet: An opening providing a means of entrance or intake.

INR (Impact Noise Rating): A single figure rating which provides an estimate of the impact sound insulating performance of a floor-ceiling assembly.

Inside Corner: The point at which two walls form an internal angle, as in the corner of a room.

Inside Drain: In roofing, a drain positioned on a roof at some location other than the perimeter. It drains surface water inside the building through closed pipes to a drainage system.

Insulating Glass: Window or door in which two panes of glass are used with a sealed air space between. Also known as Double Glass.

Insulating Glass Unit: Two or more lights of glass spaced apart and hermetically sealed to form a single-glazed unit with an air space between each light. Commonly called IG units.

Insulation: Generally, any material which slows down or retards the flow or transfer of heat. Building insulation types are classified according to form as loose-fill, flexible, rigid, reflective, and foamed-in-place. All types are rated according to their ability to resist heat flow (R-Value). In electrical contracting, rubber, thermoplastic, or asbestos wire covering. The thickness of insulation varies with wire size and type of material, application or other code limitations.

Insulation Board: A rigid structural building board made of coarse wood or cane fiber in 1/2 and 25/32 inch thickness. It can be obtained in various size sheets, in various densities, and with several treatments.

Insulation Fasteners: Any of several specialized mechanical fasteners designed to hold insulation down to a steel or a nailable deck.

Interest: The cost paid to a lender for borrowed money.

Interior Finish: Material used to cover the interior framed areas, or materials of walls and ceilings.

Interior Glazed: Glazing infills set from the interior of the building.

Interlayer: In glazing, any material used to bond two lights of glass and/or plastic together to form a laminate.

Interlocking Shingles: Individual shingles that mechanically fasten to each other to provide wind resistance.

Interply: Between two layers of roofing felts that have been laminated together.

IPS (Iron Pipe Size): Pipe thread sizing system. Also measurement of the outside diameter of a pipe.

IRMA [Insulated (or Inverted) Roof Membrane Assembly]: In this system the roof membrane is laid directly on the roof deck, covered with extruded foam insulation and ballasted with stone, minimum of 1000 lbs. per square.

Irrigation: Lawn sprinkler system.