I-Beam - A steel beam often used for floor support.
Cross section of beam resembles a capital I.
Infiltration - The act of wind blowing into the house through poorly weather-stripped windows and doors.
Inside Stop - See blind stop.
Insulation - A material designed to control the passing of heat and / or sound.
Interior Elevation - An orthographic view of an inside wall.
Ionic - The type of Greek column characterized by scroll-like decorations.