Air-leakage (air infiltration).The amount of air leaking in and out of a building through cracks in walls, windows, and doors.

Argon. An inert, nontoxic gas used in insulating glass units to reduce heat transfer. Combine Low "E" and Argon Gas to maximize the thermal performance. 40% Greater Thermal Efficiency with Low "E" and Argon.

Awning. Window similar to a casement except the sash is hinged at the top and always swings out.

Bay window. An arrangement of three or more individual window units, attached so as to project from the building at various angles. In a three-unit bay, the center section is normally fixed, with the end panels operable as single-hung or casement windows.

Brick molding. A standard milled wood trim piece that covers the gap between the window frame and masonry.

Btu (B.T.U.). An abbreviation for British Thermal Unit, the heat required to increase the temperature of one pound of water one degree Fahrenheit.

Casement. A window sash that swings open on side hinges: in-swinging are French in origin; out-swinging are from England.

Casing. Exposed molding or framing around a window or door, on either the inside or outside, to cover the space between the window frame or jamb and the wall.

Caulking. A mastic compound for filling joints and sealing cracks to prevent leakage of water and air, commonly made of silicone, bituminous, acrylic, or rubber-based material.

CFM. Cubic Feet per Minute.

Conduction. Heat transfer through a solid material by contact of one molecule to the next. Heat flows from a higher-temperature area to a lower-temperature one.

Convection. A heat transfer process involving motion in a fluid (such as air) caused by the difference in density of the fluid and the action of gravity. Convection affects heat transfer from the glass surface to room air, and between two panes of glass.

Fiberglass. A composite material made by embedding glass fibers in a polymer matrix. May be used as a diffusing material in sheet form, or as a standard sash and frame element.

Foundation - Basement
A house with a basement starts with a hole about 8 feet deep. At the bottom of the hole is a concrete slab, and then concrete or cinder-block walls form the outer walls of the basement. Actually, a basement is poured in three pieces in most cases: the "beams," then the walls, and then the slab inside the walls. This approach helps keep the basement waterproof. The L-shaped piece is a steel reinforcing bar to bind the beam and the wall together.

Foundation - Crawl Space
A crawl space has several advantages over basements and slabs:
It gets the house up off the ground (especially important in damp or termite-prone areas).
It is a lot less expensive than a basement and comparable in price to a slab.
Duct work and plumbing can run in the crawl space, meaning that they are easy to service and move over the lifetime of the house.

Foundation - Slab
The slab is probably the easiest foundation to build. It is a flat concrete pad poured directly on the ground. It takes very little site preparation, very little formwork for the concrete and very little labor to create. It works well on level sites in warmer climates -- it has problems up north because the ground freezes in the winter and this freezing can shift the slab at worst and at least lead to cold floors in the winter. A cross-section of a typical slab looks like this:

Glazing. The glass or plastic panes in a window, door, or skylight.

Glazing bead. A molding or stop around the inside of a window frame to hold the glass in place.

Greenhouse window. A three-dimensional window that projects from the exterior wall and usually has glazing on all sides except the bottom, which serves as a shelf.

Hopper. Window with sash hinged at the bottom.

Horizontal slider. A window with a movable panel that slides horizontally.

Insulating glass. Two or more pieces of glass spaced apart and hermetically sealed to form a single glazed unit with one or more air spaces in between. Also called double glazing.

Insulating value. See U-factor.

Insulation. Construction materials used for protection from noise, heat, cold or fire.

Jamb. A vertical member at the side of a window frame, or the horizontal member at the top of the window frame, as in head jamb.

Krypton. An inert, nontoxic gas used in insulating windows to reduce heat transfer.

KWH. KiloWatt Hour. Unit of energy or work equal to one thousand watt-hours.

Laminated glass. Two or more sheets of glass with an inner layer of transparent plastic to which the glass adheres if broken. Used for safety glazing and sound reduction.

Lintel. A horizontal member above a window or door opening that supports the structure above.

Mil. One thousandth of an inch, or 0.0254 millimeter.

Model Energy Code (MEC). The Model Energy Code is cited in the 1992 U.S. Energy Policy Act (EPAct) as the baseline for residential Energy Codes in the United States. It has been succeeded by the International Energy Conservation Code (IECC) published by the International Code Council (ICC).

Pane. One of the compartments of a door or window consisting of a single sheet of glass in a frame; also, a sheet of glass.

Polyvinylchloride (PVC). An extruded or molded plastic material used for window framing and as a thermal barrier for aluminum windows.

R-value. A measure of the resistance of a glazing material or fenestration assembly to heat flow. It is the inverse of the U-factor (R = 1/U) and is expressed in units of hr-sq ft-°F/Btu. A high-R-value window has a greater resistance to heat flow and a higher insulating value than one with a low R-value.

Relative humidity. The percentage of moisture in the air in relationship to the amount of moisture the air could hold at that given temperature. At 100 percent relative humidity, moisture condenses and falls as rain.

Retrofitting. Adding or replacing items on existing buildings. Typical retrofit products are replacement doors and windows, insulation, storm windows, caulking, weatherstripping, vents, landscaping.

Rough opening. The opening in a wall into which a door or window is to be installed.

Shading coefficient (SC). A measure of the ability of a window or skylight to transmit solar heat, relative to that ability for 1/8-inch clear, double- strength, single glass. It is being phased out in favor of the solar heat gain coefficient, and is approximately equal to the SHGC multiplied by 1.15. It is expressed as a number without units between 0 and 1. The lower a window's solar heat gain coefficient or shading coefficient, the less solar heat it transmits, and the greater is its shading ability.

Skylight (operable or pivot). A roof window that gives light and ventilation.

Tempered glass. Treated glass that is strengthened by reheating it to just below the melting point and then suddenly cooling it. When shattered, it breaks into small pieces. Approximately five times stronger than standard annealed glass; is required as safety glazing in patio doors, entrance doors, side lights, and other hazardous locations. It cannot be recut after tempering.

Thermal break. An element of low conductance placed between elements of higher conductance to reduce the flow of heat. Often used in aluminum windows.

Thermal expansion. Change in dimension of a material as a result of temperature change.

Threshold. The member that lies at the bottom of a sliding glass door or swinging door; the sill of a doorway.

Transom. A horizontal transverse beam or bar in a frame; a crosspiece separating a door or the like from a window or fanlight above it. Also, a window above a door or other window, built on and commonly hinged to a transom.

Transom window. The window sash located above a door. Also called transom light.

Triple glazing. Three panes of glass or plastic with two air spaces between.

U-factor (U-value). A measure of the rate of non-solar heat loss or gain through a material or assembly. It is expressed in units of Btu/hr-sq ft-°F (W/sq m-°C). Values are normally given for NFRC/ASHRAE winter conditions of 0° F (18° C) outdoor temperature, 70° F (21° C) indoor temperature, 15 mph wind, and no solar load. The U-factor may be expressed for the glass alone or the entire window, which includes the effect of the frame and the spacer materials. The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating value.

Ultraviolet light (UV). The invisible rays of the spectrum that are outside of the visible spectrum at its short-wavelength violet end. Ultraviolet rays are found in everyday sunlight and can cause fading of paint finishes, carpets, and fabrics.

Weatherstripping. A strip of resilient material for covering the joint between the window sash and frame in order to reduce air leaks and prevent water from entering the structure.