The Fenestration Glossary

TERM	MEANING
daylight transmittance	The percentage of visible light that glazing transmits through a window -- a standard clear dualpane has a daylight transmittance of 82%.
debridge	the process of cutting away the metal on the bottom of an aluminum thermal break cavity once the two-part polyurethane has reached full strength, thus creating a thermally broken extrusion.
desiccant	a porous crystalline substance used to absorb moisture and/or sealant solvents from within the sealed air space of an insulating glass unit.
design load	the project wind load to be determined by the architect and expressed in psf, e.g., "the project design load shall be 38.7 psf, both positive and negative."
designation number	prescribed by AAMA. One for each window style. It provides a code for architectural selection, e.g., TR-5000 = DH-C45 = Double Hung - Commercial Grade - 45 psf Design Pressure.
dessicant	Crystalline substance used to absorb moisture from air within IGUs.
dew point	The temperature at which water vapor will condense as warm, moist air is cooled.
die	a perforated steel block through which aluminum or vinyl is extruded.
direct gain	A direct gain passive solar system utilizes south-facing windows to open a house to the sun. A large window area accepts direct sunlight while thermal mass serves as storage.
dormer	A space which protrudes from the roof of a house, usually including one or more windows.
double glazing	Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.
double glazing panel (dgp)	A removable interior glass panel which creates an air space between the exterior glazing and itself. It provides improved insulation and condensation control and allows for between-glass shading options such as muntins, blinds and pleated shades.
double strength glass	(DSB) 1/8" thickness.
double-hung window	A window unit that has two operable sashes which move vertically in the frame. Two vertically sliding sash which by-pass each other in a single frame. Sashes typically fit within vinyl balances and tilt out and remove for safe, easy cleaning.
drip cap	A molding placed on the top of the head brickmold or casing of a window frame.
dry glazing	a method of securing glass in a window frame with a dry, preformed, resilient gasket, without the use of a glazing compound.
dual durometer	A material that has two or more levels of flexibility. An example is the weatherstripping used between the frame and sash of a Pella casement window.
dual durometer bead	a vinyl glazing bead with a softer flap against glass and a harder section inserted into sash member.
dual glazed	two single lites glazed into a split sash with an airspace, not hermetically sealed, between the two single lites.
dual window	two windows joined together, one in front of the other, to provide superior sound control.
dualpane	Two panes of glass with a single airspace, held together by an edge spacer -- the most economical IGU.
edge of glass	The glass area within 2 1/2" (10cm) of the edge of a window.
egress window	a window with specific release hardware and minimum clear opening size to allow occupants to escape through the window in case of a fire.
electrostatic	a painting process by which the aluminum is grounded and the paint carries a positive electric current. This creates a magnetic attraction between the paint and the aluminum allowing for uniform paint coverage on all exposed extrusion surfaces.
emissivity	Emission, or the ability to radiate heat in the form of long-wave radiation.
end dam	used to close the ends of a subsill so the water will not leak out the ends. It makes the subsill a complete water trough allowing it to collect excess water and drain it to the exterior.
EPDM	Ethylene Propylene Diene Monomer - a weather resistant synthetic rubber from which many flexible gaskets for windows are made.
EPDM	Ethylene Propylene Diene Monomer - a weather resistant synthetic rubber from which many flexible gaskets for windows are made.
ER Rating	Energy Rating number developed by CSA (Canadian Standards Association) to compare the thermal performance of windows. Measured in watts per square meter (W/m2).
escutcheon plate	hardware for handles etc.
expansion mullion	self mulling window frame jambs that, when slipped together, permit expansion/contraction while preserving strength and watertightness.
extension jambs	Flat wood parts which are nailed to the interior edges of the window jamb to extend it in width and adapt to a thicker wall. The inside edge of extension jambs should be flush with the finished wall surface. Interior casing is then nailed into it.
exterior glazed	glass glazed from the exterior of the building.
extrude	the process of shaping aluminum or vinyl by forcing it through a die.
extrusion	the finished form after pushing aluminum or vinyl through the die.
extrusion	A form produced by forcing material through a die. Pella window frames are clad with extruded aluminum.
fenestration	An architectural term referring to the arrangement of windows in a wall. From the Latin word, "fenestra," meaning window.
fenestration	The arrangement of windows in a building.
fin seal	a form of pile weatherstrip that has a plastic mylar fin centered in the pile. This fin reduces air infiltration and ensures weatherstrip contact throughout the window's life.
finger-jointing	A means of joining individual pieces of wood together to form longer lengths. The ends of the pieces are machined to form a set of interlocking fingers, which are then coated with adhesive and meshed together under pressure.
fixed	Non-venting or non-operable.
fixed unit	A stationary window or door that does not open -- also referred to as a fixed sash.
flange frame	a window frame with the head, jamb, and sill exterior perimeter leg longer than the interior perimeter leg.
flashing	A thin strip of metal or synthetic material that diverts water away from a window or skylight. A metal or plastic strip attached to the outside of the side jambs and head to provide a weather barrier, preventing leakage between the window frame and wall.
float glass	transparent glass with flat, parallel surfaces formed on the surface of a pool of molten tin.
foam spacer	Foam material placed in the airspace of the insulating glass windows to enhance the appearance and improve the performance of the window.
frame	The enclosure in which window sash or door panels are mounted. Outside members of a window unit which enclose the sashes. Composed of side jambs, head jamb and sill.
frame	Consists of a head, jambs, and sill to form an opening into which sash or door panels fit.
French hinged door	Hinged door(s) which have wider panel members around the glass.
French sliding door	A sliding door which has wider panel members around the glass, giving the appearance of a French hinged door.