Air Chambers - Small spaces within the sash and frame that help to insulate and strengthen the window.
Air Infiltration - The amount of air that passes between a window sash and frame. In windows it is measured in terms of cubic feet or air per minute, per square foot of area. The lower the number, the less air the window lets pass through.
Argon Gas - An odorless, colorless, tasteless, non-toxic gas, which is six times more dense than air. It is used to replace air between the glass panes to reduce temperature transfer.
Awning Window - A top-hinged window that swings outward for ventilation.

Bay Window - An angled combination of three windows that project out from the wall of the home. The windows are commonly joined at 30- or 45-degree angles.
Bow Window - An angled combination of windows in 4-, 5- or 6-lite configurations. The windows are attached at 10-degree angles to project a more circular, arced appearance.
Butyl - A rubber material that seals the glass to the spacer, creating an airtight and watertight I.G. Unit. Butyl has the lowest gas permeability of all rubbers.

Cam Lock and Keeper - The mechanisms that pull the sash together when placed in the locked position.
Casement Window - A window with a side-hinged sash that opens outward for ventilation.
Center of Glass U- and R-values - The U- and R-values measured from the center of the glass to 2-1/2" from the frame.
Conduction - Energy transfer from one material to another by direct contact.
Convection - Heat transfer by currents that flow from a warm surface to a colder one.

Dead-air space - The space between the panes of glass of an I.G. Unit.
Desiccant - A material used in insulating glass to absorb water vapor that causes fogging.
Double Hung Window - A window that has two operable sashes that slide vertically.
Double-strength Glass - Glass with a thickness of approximately 1/8".

Egress Code - The construction code that requires a minimum opening of a window for persons to exit or firefighters to enter a building.
ENERGY STAR® - ENERGY STAR® is an independent U.S. government program establishing a standard set of guidelines to recognize the energy efficiency of various products. ENERGY STAR® guidelines are used in conjunction with a variety of building materials, including windows and patio doors. Over the past ten years, ENERGY STAR® guidelines have helped double the efficiency of windows they endorse.

Fenestration - The design and placement of openings in a building, including windows and doors.
Fenestration Product - Any transparent or translucent glazing material plus any associated sash, framer mullions and/or dividers, in the envelope of a building, including, but not limited to windows, sliding glass doors, French doors, skylights, curtain walls and garden windows.
Fusion-welded - The process of joining materials by melting them together with extreme heat (over 500ºF), resulting in the materials uniting into a one-piece unit.

Geometric - Specially designed windows classified as either Straight-line Geometrics, such as rectangles, triangles, trapezoids, octagons, pentagons, etc., or Radius Geometrics, which include half-rounds, quarter-rounds, full-rounds, sectors, ellipses, eyebrows, etc.
Glass - An inorganic transparent material composed of sand (silica), soda (sodium bicarbonate), and lime (calcium carbonate) with small quantities of alumina, boric or magnesia oxides.
Glazing - The process of sealing the glass to the sash.
Grids - Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being dividing into smaller areas of glass.

Head - The horizontal top portion of the main frame.

Laminated Glass - Two or more pieces of glass bonded together over a plastic interlayer.
Lift Rail - A handhold for raising and lowering the sash. Rail implies that the handhold is continuous across the sash.
Lock Stile - The vertical section of the sash where the cam lock is attached.
Low E (Emissivity) Glass - Glass with a transparent metallic oxide coating applied onto or into a glass surface. The coating allows short-wave energy to pass through, but reflects long-wave infrared energy to improve the U-value.

Main Frame - The head, sill and jamb sections of a window.
Mechanically Fastened Frame - Refers to frames fastened with screws.
Meeting Rail - The horizontal sections of a pair of sash that meet when the sash are closed.
Meeting Stile - The vertical section of a pair of sash that meet when the sash are closed.
Mesh - Fabric of either fiberglass or aluminum that is used to make screens.
Mullion - A vertical or horizontal connecting unit between two or more windows.

Nailing Fin - An extrusion attached to the main frame of a window, which is used to secure the unit to the rough opening.

Oriel - A window with the meeting rail located off-center of the frame.

Patio Door - A glass door that slides open and closed on adjustable tandem rollers.

R-value - Resistance that a material has to heat flow. The higher the R-value, the greater the resistance.
Radiation - Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is either transmitted, absorbed, reflected or a combination of all three.
Rail - The horizontal sections of the sash.
Relative Humidity Condensation Point - The relative humidity level at which visible water vapor or other liquid vapor begins to form on the surface of the sash or frame, based on an inside temperature of 70°F and an outside temperature of 0°F. The higher the percentage, the more moisture the air can hold before condensation will occur.

Sill - The horizontal, bottom section of the main frame.
Sill Extender - An extrusion that is attached to the bottom of the window to cover the gap between the sill and the rough opening.
Single Hung - A window in which one sash slides vertically and the other sash is fixed.
Single-strength Glass - Glass with a thickness of approximately 3/32".
Slider Window - A window in which the sash moves horizontally. Sliders are available in a 2- or 3-lite configuration, with the 3-lite having operable end vents.
Sloped Sill - The sill of the window that has a downward slope to the outside. This sill has sufficient degree of slope to aid in water runoff.
Solar Heat Gain - The percentage of heat gained from both direct sunlight and absorbed heat. The smaller the number, the greater the ability to reduce solar heat gain.
Spacer - Material placed between two or more pieces of glass to maintain a uniform width between the glass, and to prevent sealant distortion.
Stile - The vertical sections of the sash.

Tape Glazing - Two-sided tape used to secure and seal the glass to the sash.
Tempered Glass - Glass with a surface compression of not less than 10,000 psi, or an edge compression of not less than 9,700 psi. When broken, the glass breaks into pebbles instead of shards.
Tilt Latch - The mechanism that unlocks the sash and allows it to tilt in from the main frame.

U-value - Amount of heat transferred through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality.
UV Block - The percent of ultraviolet rays blocked from being transmitted through the glass. The higher the number, the lower the percentage of ultraviolet rays transmitted through the window.

Visible Light Transmittance - The percentage of light that is transmitted through glass in the visible light spectrum (380 to 720 nanometers). The higher the number, the higher the percentage of visible light transmitted through the window.

Weep Flaps - A weep hole that is covered with a flap that allows water to escape, while keeping insects out.
Weep Holes - Small openings designed to allow water to escape that might otherwise accumulate in a window's sill.
Wet Glazing - A silicone-based substance used to secure and seal the glass to the sash.

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