The Fenestration Glossary

TERM	MEANING
AAMA	American Architectural Manufacturers Association - a window industry organization that establishes voluntary standards, e.g., AAMA 101-93, certification to those standards, and designations, e.g., DH-C45 for the TR-5000.
adjustment clip	hardware on hung window jambs to align jamb after window installation.
AIF.	Acoustic Insulation Factor, a sound transmission measure used in Canada
air infiltration	the amount of air leaking in and out of a building through cracks in walls, windows, and doors (the lower, the better).
ambient temperature	The outdoor temperature.
anodize	the process that provides a hard, durable oxide film on the surface of aluminum, by electrolytic action.
apron	Interior flat trim piece which is used under the stool at the bottom of the window.
argon	An inert, colorless, and harmless gas used instead of air in sealed spaces between panes of glass in insulating glass units to increase insulation. Argon is less conductive to heat than air.
ASHRAE	American Society of Heating, Air-conditioning and Refrigeration Engineers.
astragal	The center member of a double door, which is attached to the fixed or inactive door panel.
awning	A type of window with a top-hinged sash that swings out at the bottom -- lets in fresh air while keeping rain out.
awning window	A window unit in which the bottom of the sash swings outward.
back bedding	The process of adhering and sealing.
balance	a mechanical device, normally spring loaded, used in hung windows to counterbalance the weight of the sash during opening and closing.
balance shoe	nylon hardware in hung window jamb that connects the balance with the sash.
bay window	A composite of three windows, usually made up of a large center unit and two flanking units at 30- or 45-degree angles to the wall. A bay projects from the wall of the structure.
bead	a molding or stop placed around a window frame to hold the glass in place by pressure.
billet	the cylindrical form of aluminum just prior to the extruding process.
bite	a glazing term referring to the dimension of the glazing leg which overlaps the edge of the glass.
bow window	A composite of four or more window units in a radial or bow formation gently curved contour. Bow windows also project from the walls of the structure.
brickmold	A type of external casing which frames windows and doors. Exterior casing around window to cover jambs and provide means for nailing during installation.
BTU	British Thermal Unit -- a basic measurement of heat. One BTU equals the amount of heat needed to raise one pound of water 1 degree Fahrenheit. (A match contains approximately one BTUs, and a well-insulated house in the Ottawa region may require 90 million BTU for space heating over the year). The metric equivalent is 1054.35 Joule.
casement	A type of window with a side-hinged sash that opens like a door -- the best window for catching breezes and providing cross-ventilation.
casement window	A window unit in which the single sash cranks outward, to the right or left. Projecting window hinged at the sides and usually opening outward like a door.
casing	Molding of various widths, thickness and shapes applied to the framework of window and door units. Interior casing is a flat, decorative moulding which covers the inside edge of the jambs and the rough opening between the window unit and the wall. Exterior casing (or brick mould) serves the same purpose, while it also is an installation device through which nails are driven to install the window unit into the wall.
caulking	Sealants used to seal fixed and movable construction joints and prevent infiltration.
center of glass	All glass area of a window except that within 2.5" (10cm) from the edge of the glass -- used in measuring and calculating glazing performance such as R-values and U-values.
cfm	cubic feet per minute - a unit of measure used in air infiltration testing, e.g., "maximum .10 cfm per foot of sash perimeter."
check rail	On a double-hung window, the bottom rail of the upper sash and the upper rail of the lower sash, where the lock is mounted. The top rail of the lower sash and the bottom rail of the upper sash which meet when a double-hung window is closed. Both pieces should be weather stripped for maximum weatherability.
circlehead	A generic term referring to any of a variety of window units with one or more curved frame members, often used over another window or door opening.
cladding	An aluminum material locked to the outside faces of many Pella products to provide a durable, low-maintenance exterior surface.
clerestory	A window placed vertically in a wall above one "s line of vision to provide natural light -- often at the intersection of two offset roof planes.
clerestory window	A venting or fixed window above other windows or doors on an upper outside wall of a room.
CMR	Centerline of Meeting Rail - a reference line used to locate integral mullions and/or size oriel (unequal) sash, e.g., "the height of the lower sash shall be 22" from the frame sill to CMR."
collection	The act of trapping solar radiation and converting it to heat.
comfort engineering	Optimizing glazing selections on a window-by-window basis to fulfill a prioritized set of objectives -- e.g., comfort, energy efficiency (both summer and winter), UV protection, natural lighting, desired aesthetics, views, and budget. Willmar Windows" sales consultants act as expert comfort engineers, finding appropriate solutions for individual needs.
condensation	The change of a gas to a liquid state. Because warm air can hold more water vapor than cold air, as warm air cools its ability to hold water vapor is reduced. Excess moisture condenses on the warm side of glass. e.g., condensation on the outside of a glass of ice-water.
conduction	A process of heat transfer whereby heat moves directly through a material by molecular agitation.The handle of a cast-iron frying pan becomes hot due to conduction.
conductivity	The transfer of heat through a given material -- see U-value which is the measure of conductivity, the inverse of R-value.
convection	A process of heat transfer whereby heat energy is transferred from one location to another -- created by the motion of air resulting from a difference in temperature and the action of gravity.
cottage double-hung	A double-hung window in which the upper sash is shorter than the lower sash.
crack length	total outside perimeter of window sash/vent; used when defining the AAMA air infiltration rate.
CRF	Condensation Resistance Factor - an indication of a window"s ability to resist condensation (the higher the better).
curb appeal	The visual attractiveness of a home as seen from the street -- often the first impression. Realtors see curb appeal as an influential factor in evaluating and selling homes.
custodial lock	window hardware only operable with a tool or key.