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 or from 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.