Vapor barrier: A watertight material used to prevent the passage of moisture into or through floors, walls and ceilings.

Vent: The movable sash or framework in a glazed window that is hinged or pivoted to swing open.

Vinyl-clad window: A window with exterior wood parts covered with extruded vinyl.

Venting unit: A window or door unit that opens or operates.

Visible transmittance (VT). Measures the amount of visible light that is transmitted through the glass.