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Doors and Vinyl Windows Terms and Definitions

Your guide to key understand industry terms


Air Chambers - Air chambers are spaces built into a window frame that make the window stronger and being shaped like a honeycomb, they improve insulation. 

Air infiltration - Air infiltration refers to how much air can get through the window frame. It's expressed as how many cubic feet of air pass through a square foot of the frame, per minute. 

Air latch - An air latch keeps a window open at whatever position you set it. 

Airspace - Airspace size is equal to ½" to ¾" between the panes of glass in a window. 

Argon gas - Argon gas is nontoxic, colorless, odorless and tasteless. Since it's 6 times denser than air, it dramatically reduces heat loss when used between panes of glass in a window. 

Astragal - The center member of a double door, which is attached to the fixed or inactive door panel. 

Awning Window - This window has a top hinge that swings outward from the bottom for proper ventilation.


Balance system - A balance system uses springs or weights to hold a window open at the position you set it. 

Beveled exterior - An angled extension from the frame on the exterior of a house. 

Bay window - The combination of three windows that stick out from the wall of the house, with the middle window parallel to the house is called a bay window. The other windows are set at 30- to 45-degree angles, connecting the front window to the house. 

Bow window - A bow window sticks out from a house like a bay window. The difference is the number of windows – there are 3, 4 or 5, attached at 10-degree angles, creating a semi-circular look. 

Brick mold - The brick mold is the exterior casing around a door or window that covers the jambs. 

Butyl - A hot rubber sealant, butyl, seals the glass to the spacer so no air or water can get in.


Cam lock and keeper - A cam lock and keeper is the window handle part that keeps it in the locked position. 

Capillary tubes - Capillary tubes are small hollow tubes that penetrate the spaces of glass and allow pressure to be equalized at all times. 

Casement window - A casement window is hinged on both sides, allowing for a tighter fit, since the sash closes against the frame. A casement window can be opened outward, allowing for better ventilation. 

Casing - Inside casing is a flat, decorative moulding that covers the inside edge of the jambs and the rough openings between the window unit and the wall. Outside casing (or brick mould, above) serves the same purpose, while it also is an installation device through which nails are driven to install the window unit into the wall. 

Center of glass U- and R-values - The U- and R-values are measured from the center of the glass to 2-1/2" from the frame. 

Condensation resistance factor - The condensation resistance factor tells you how well a window reduces condensation. The higher the number, the better it works. 

Conduction - Conduction occurs when two materials contact each other and pass energy between them. 

Coved exterior - A coved exterior is an arced extension of a window on the outside of a house.


Dead-air space - Dead-air space is the air-space between the two panes of a double- or triple-pane window. 

Desiccant - Because of it's water absorbency, desiccant is used in insulating glass to prevent windows from fogging up. 

Double-hung window - A double-hung window is a window that slides or opens up and down. 

Double-strength glass - Double-strength glass is about 1/8” thick. 

Dry glazing - An alternative method of placing glass in a door or window is called dry glazing.


Egress code - The egress code is a law that specifies that a window must be able to open wide enough for a person to get out, or a firefighter to get in. 


Fusion-welded - Fusion-welding melts materials together at 500º or more, thus creating one piece.


Geometric Windows - Specially designed windows classified as either Straight line Geometrics such as rectangles, triangles, trapezoid, octagons, pentagons, etc., or Radius Geometrics which include half-rounds, quarter-rounds, full-rounds, sectors, ellipses, eyebrows, etc. 

Glass - Glass is a transparent material made up of sand, soda, and lime. 

Glazing - Glazing is the art of attaching a pane of glass to a frame, then sealing it in place. 

Glazing bead - A glazing bead is a strip of vinyl placed around the edge of a piece of glass. This holds it in place along with other sealants. 

Grids – Grids(grills) are bars put on a window to divide the larger pane into what looks like smaller panes.


Head - The head is the part of the frame at the top of the window. 

Head expander - A vinyl shape cut the width of a product and placed on the head, fitting over it snugly. This piece is used as a filler to expand or lengthen the unit from the head and take up the gap in the opening between the unit and the opening in the unit. 

Hermetically sealed - Hermetically sealed windows are completely sealed against the escape or entry of air. 

Hopper - A hopper is a window that's hinged on the bottom, allowing it to open inward. 


I.G. (Insulating Glass) unit - An I.G. unit is a double- or triple-pane window, with air-space between the panes, and sealed at the edges. 

Insulating glass - Insulating glass is two or more pieces of glass enclosing a hermetically sealed airspace to reduce thermal loss.


Jamb - The jambs are the parts of the frame on either side of the window.


Keeper Rail - The horizontal section of the sash where the keeper is attached. 

Keeper Stile - The vertical section of the sash where the keeper is attached. 

Krypton gas - Krypton gas is used for the same purpose as argon gas. The difference is that it's twice as dense as argon, or 12 times denser than air.


Laminated glass - Laminated glass is made by bonding a tough protective layer or polyvinyl butyral (PVB) between two panes of glass under heat and pressure. 

Lift handle - A lift handle is simply the handle used to open and close a window. 

Lift rail - A lift rail is the same as a lift handle, except it goes all the way across the sash. 

Lite - A unit of glass in a window. 

Low-emissivity (Low-E) glass - Low-E glass has a special clear coating on it that blocks infrared energy from passing through it. 


Main Frame - The head, sill and jambs sections of a window. 

Mechanically-fastened frame - A mechanically-fastened frame is put together using screws, as opposed to fusion-welding. 

Mesh - Mesh is a fabric made of fiberglass or aluminum used for screens on windows and doors. 

Mullion - A vertical or horizontal connecting unit between two or more windows. 

Muntin bar - A muntin bar, also known as a grille or a mullion, is a bar that's used to divide panes. 


Obscure glass - Obscure glass is translucent, rather than transparent, and is used for such places as bathroom windows. 


Patio door - A patio door is made up of two panes of glass, slides open and closed but has only one operable sash. 

Picture window - A picture window is usually very large and has a sash that can't be moved. 


Radiation - Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is transmitted, absorbed, reflected or a combination of all three. 

Rail - The rail is the horizontal part of the sash. 

R-value - The R-value of a window refers to the amount of heat loss it allows. The higher the number, the less heat is lost. R-values today can go from 0.9 to 4.0, or even more. 

Rail - The rails are the parts of the sash that are horizontal. 


Sash - The sash is the part of the window that holds the pane. 

Shading Coefficient - The ratio of solar heat that is transferred through a glazing material relative to the solar heat transferred through 1/8" clear glass. The lower the number- the more efficient the window is at reducing solar heat gains. 

Sill - The sill is the bottom part of the 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 single-hung window is the same as a double-hung window, except the top sash doesn't move. 

Single-strength glass - Single-strength glass is about 3/32” thick. 

Slider window - A slider window moves back and forth, as opposed to up and down. 

Sloped sill - A sloped sill is the outside of the window sill, and is sloped downward to allow water to run off. 

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 in order to maintain a uniform width between the glass, and prevent sealant distortion. 

Stile - The stiles are the parts of a frame that run up and down. 


Tempered glass - Tempered glass is specially treated, so that when it breaks, it shatters into little pieces. 

Transom - A transom is a horizontal crosspiece(window) over a door or between a window and a door. It refers to a small, hinged window above a door or another window. 

Tilt latch - A tilt latch unlocks the sash and allows it to tilt in from the main frame. 

Total Unit U- and R-values - The U- and R-values of the window calculated from the average U and R-values from the center of glass, edge of glass, and frame. 


U-value - A window's U-value refers to how much heat passes through the glass. The lower the U-value, the better the insulation.


Vent-lock - Latch mechanism on the interior face of the sash which retains the window in a partially open position for ventilation. 

Visible light transmittance - The percentage of light that is transmitted through glass. The higher the number the higher the percentage of light transmitted through the window. 


Weather-stripping - Material used to form a weather-resistant seal around operable sash. 

Weep flaps - Weep flaps are little vinyl-covered holes that let water escape, while keeping bugs out. 

Weep slots - Weep slots are holes in the sill that let water run outside. - See more at: http://citywindow.com/terms.php#sthash.ZdZ7f9fY.dpuf