Kilowatt (kw) - One thousand watts. A kilowatt hour is the base unit used in measuring electrical consumption. Also see watt.
Laminating - Bonding together two or more layers of materials.
Latch - A beveled metal tongue operated by a spring-loaded knob or lever. The tongue's bevel lets you close the door and engage the locking mechanism, if any, without using a key. Contrasts with dead bolt.
Lath and Plaster - The most common wall finish prior to the introduction of drywall. Thin wood strips (lath) were nailed onto the framing as a base for the sand/lime plaster (see diagram).
Level - True horizontal. Also a tool used to determine level.
Life - The average number of hours a bulb will burn.
Life-cycle cost - The total cost of purchasing, owning and maintaining a device, including the cost of energy used to operate the device, over the lifetime of the device.
Lighting efficiency - Expressed as Lumens per Watt. A measure of efficiency similar to miles per gallon. The best choice is usually the highest light output (Lumens) for the least power consumed (Watts).
Limit switch - A safety control that automatically shuts off a furnace if it gets too hot. Most also control blower cycles.
Lineal foot - A unit of measure for lumber equal to any thickness by any width by 12 inches long. Example: 2" x 6" x 14'=14 lineal feet. 1" x 6" x 14'=14 lineal feet.
Lintel - A load-bearing beam over an opening in masonry, such as a door or fireplace.
Liquefaction - The process of converting a gas to a liquid, either by removal of heat or an increase in pressure.
Load Bearing Wall - A wall which is supporting its own weight and some other structural elements of the house such as the joists.
Load management - Control of energy consumption at any instant through the use of mechanical or electronic devices or conscious consumer limitations on the use of energy-consuming devices.
Lumens - Unit of measure for total light output.
Luminaire - A glass or metal fixture that reflects or diffuses light from a bulb.