Air Infiltration:  Industry test that measures the amount of air leakage through a window or door (the lower the number the better).

Annealed Glass:  Standard float glass. Glass without internal stresses caused by heat treatment.

Apron:  Decorative trim positioned directly underneath a window stool and installed flush against the wall.

Arch Window:  Four-sided unit with a curve at the top.

Argon Gas:  Colorless, odorless gas used in the air space of double pane Low-E glass to increase the insulating performance.

Art Glass:  Decorative glass in a variety of colors/shapes/patterns used to accent a window or door.

Astragal:  Center post of a double door attached to the fixed or inactive door panel.  

Awning Window:  Unit with hinged sash that swings outward from the bottom; allows ventilation at the bottom.

Balancer:  Counter-weight mechanism to assist raising or lowering of a double-hung or single hung sash.

Bay Window:  Window consisting of three or more units that angle out beyond the wall; often configured with a large center unit and two flanking units.

Bow Window:  Window consisting of three or more units projecting out from wall to form a radius.

Brick Mould:  Exterior trim around the window frame traditionally used to attached the window to the wall.


Casement Window:  Unit with hinged sash that opens to the side; allows top to bottom ventilation.

Casing:  Flat, decorative molding used on the interior perimeter of a window or door that covers the space between the unit and rough opening or between units.

Cast Glass:  Glass that is cut and fabricated, then put into a kiln and heated up on a mold, taking on the texture of the mold. It can be used in any configuration and is amazingly beautiful.

Check Rail:  Located on double-hung windows where the bottom sash and top sash meet and the lock/keeper is mounted.

Circle Top™ (Half Round) Window:  Half circle unit consisting of a curved top and linear bottom.

Cladding:  Low maintenance covering or coating attached to the unit exterior.

Clear Opening:  The size of the opening created when a unit is in a full open position.

Clerestory:  Window located up high on wall; typically unreachable from ground level.

Coil Stock:  Roll aluminum that is bent into shape to form a transition piece between the unit exterior and siding/trim.

Combination Unit:  Storm window and insect screen contained in a single frame.

Condensation:  Water that collects as droplets on the glass/sash/panel interior or exterior under certain conditions (typically cold services when exposed to humidity).

Cornice:  An ornamental molding at the top of the window positioned above the exterior trim.

Cottage Window:  Double-hung window where the upper sash is shorter than the bottom sash.

Damage Function:  Percent of the Ultra-Violet (UV) and Visible Light energy from the sun that can cause fabric fading. The lower the number, the less potential for fabric fading. Preferred over just looking at UV transmission.

Daylight Opening:  Visible glass area.

Decorative Drip Cap:  An ornamental trim piece positioned at the top of the window above the exterior trim that directs water away from the top of the window.

Double-hung:  Venting upper and lower sash in a single frame that slide vertically past one another.

Egress Window:  A venting window required by buiding codes for emergency escape and rescue, which are typcially required in bedrooms and which are required to meet certain minimum opening dimensions.

Equal Lite:  Window or door with equal spaced grille bars.

Escutcheon Plate:  Decorative door handle plate that conceals the locking mechanism.

Extension Jamb:  Wood component fastened to the interior of the window/door that extends the window frame out to the wall depth.

Exterior Trim:  A decorative trim positioned around the exterior perimeter of a window or door.

Fenestration: Refers to an opening in a structure such as windows, doors and skylights. Can also refer to the placement of windows and doors in a building.

Float Glass: The process through which clear and tinted glass are made.

Frame: The combination of the head, jambs and sill that form an exact opening in which a window sash fits.

Framed: Enclosures where there are metal channels running all the way around the shower door or doors. Generally these have a tighter seal than semi-frameless or frameless to help keep more water splashes in the shower.

Frameless: Enclosures where there are no metal channels around the sides of the shower door or doors.

French Casement Window: Unit with two venting sash that open outward to provide a large center opening with no center post.

French Door: Hinged door(s) with large glass area surrounded by a wide wood side stiles and a tall bottom rail.

Full Divided Light: Grille intended to replicate the look of a True Divided Light unit; consists of an interior grille, exterior grille and spacer between the glass panes.

Full Frame: Frame intended for installation direct to the rough opening; opposite of insert window.

Glazing: Glass in a window sash or door panel; the act of installing glass in a window sash or door panel.

Glazing Bead: Wood or vinyl pieces around the perimeter of the glass that covers the space between the glass edge and sash/panel.

Gliding Door/Sliding Door: Door with two or more panels where one panel slides horizontally past another.

Gliding Window/Sliding Window: Window with two sash, where one sash slides horizontally past the other.

Grilles: Any bar that divides window glass into smaller panes. Also called a muntin, grid or windowpane divider.

Head: The main horizontal part forming the top of the window frame.

Heat-strengthened Glass: Glass twice as strong as regular annealed glass of the same size and thickness. It also is able to withstand greater wind loads ad impacts. When broken, it fractures into large, jagged pieces.

Heavy Glass: Enclosures which are made with glass thicker than 1/4”. Most are made with 3/8” glass, with some being made with 1/2” glass or 5/16” glass.

High Altitude Capillary Breather Tubes: Very small diameter tubes placed within the unit that allows equalization of the air space due to high elevation pressure differences.

Insulated Glass Units (IG Units):  Double pane windows separated with gas insulators. The units reduce the tendency of condensation to form on the interior of the glass. They also reduce cold transmittance and help maintain a uniform temperature.

Jamb:  The main vertical parts forming the sides of a window frame.

Laminated Glass:  Layered glass that resists breakage and holds together when broken.

Low-E glass: Glass with a low-emissivity coating that restricts heat loss.

Low-emissivity: Glass coated with a low-emissivity substance can reflect radiant infrared energy, encouraging radiant heat to remain on the same side of the glass from which it originated, while letting visible light pass.

Low-maintenance (Low-e) Glass: It allows sunlight into a room without letting heat escape and resists ultraviolet light, which results in less fading of home décor. Low-e glass also reduces glare.

Pane:  A framed plate of glass within a window frame.



R-value:  Measures the overall resistance to heat transfer. The higher the R-value, the less heat is transmitted through the glass.

Reflective Glass:  Clear or tinted glass with a thin layer of metal or metallic oxide on the surface. The reflective coating reduces heat gain, solar radiation and glare from the outside while allowing visible light to enter. A mirror-like appearance.

Rolled Glass:  The process through which patterned or wired glass is made.

Sash: A single assembly of stiles and rails made into a frame for holding glass.

Seal: A compressible surface that inhibits air and water passage

Semi-frameless: Enclosures where there are metal channels on some but not all sides of the shower door.

Shading Coefficient (SC): A measure of a window’s ability to transmit solar heat, relative to that ability for 1/8-inch clear glass. The lower a unit’s shading coefficient, the less solar heat it transmits, and the greater its shading ability. It is being phased out in favor of the solar heat gain coefficient (SHGC).

Sill: The main horizontal part forming the bottom of the frame of a window.

Single-hung: Double-hung styled window in which the top sash is inoperable

Tempered Glass: Glass four times as strong as annealed glass of the same size and thickness. It offers greater strength against deflection and better resistance to the force of wind than heat strengthened glass. When broken, it shatters into cube-shape pieces.

Tinted Glass: Glass to which a small amount of color has been added consistently throughout the glass batch. The tinting reduces glare and absorbs heat.

Tub Enclosure vs. Shower Enclosure: Units shorter than 63” in height are generally considered tub enclosures, although you can certainly use a taller unit on a tub.

U-value:  Measures the heat that is gained or lost through glass due to the difference in the indoor and outdoor temperatures. The lower the U-value, the less heat is transmitted through the glass.