I-beam  A steel beam with a cross section resembling the letter I. It is used for long spans as basement beams or over wide wall openings, such as a double garage door, when wall and roof loads bear down on the opening.

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

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

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

Infiltration  The passage of air from indoors to outdoors and vice versa; term is usually associated with drafts from cracks, seams or holes in buildings.

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

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

Insulation board, rigid  A structural building board made of coarse wood or cane fiber in ½- and 25/32-inch thickness. It can be obtained in various size sheets and densities.

Insulation  Any material high in resistance to heat transmission that, when placed in the walls, ceiling, or floors of a structure, and will reduce the rate of heat flow.

Interest  The cost paid to a lender for borrowed money.

Interior finish  Material used to cover the interior framed areas of walls and ceilings

Irrigation  Lawn sprinkler system.