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B

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.

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C

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 window 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.

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.

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D

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 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.

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E

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.

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F

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.

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G

gasket--a rubber or plastic pliable material used to separate glazed glass and aluminum or vinyl.

glazing--Glass in a window or door; the act or process of fitting glass or panels into the sash or frame of the window.

glazing--The installation of glass into a window or door sash. Also refers to the type of glass used in the process.

glazing bead--a molding or stop around a window frame to hold the glass in place by pressure. A vinyl or wood strip, applied around the perimeter of the glass on the exterior of the window sash, for holding the glass in place.

glazing stop--The part of the sash or door panel which holds the glass in place.

greenhouse effect--The property of glass that permits the transmission of short-wave solar radiation, but is opaque to long-wave thermal radiation. The interior of a car heating up in direct sun illustrates the greenhouse effect.

grille--A term referring to windowpane dividers or muntins, usually a type of assembly which may be detached for cleaning.

grilles--Decorative inserts for windows or door glazing that add a traditional touch -- available as fixed or removable inserts, in wood, brass, or vinyl.

grilles-between-the glass--Aluminum bars in varying thicknesses and profiles sealed between insulating glass panels to simulate muntin bars.

gusset--a concealed, strong, right-angled shape used to reinforce mitered corners in tubular aluminum extrusions

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H

head--The main horizontal member forming the top of the window or door frame.

head board--A flat board, cut to fit the contour of a Bow or Bay window, for installing between the head jambs and the flat wall surface to finish off the area which would normally be ceiling.

head expander--a u-shaped extrusion slipped over the frame head that, when pushed up, closes the gap above the window after window installation.

header--A horizontal framing member placed over the rough opening of a window to prevent the weight of wall or roof from resting on the window frame. A beam across the top of the rough opening for a window or door. Headers rest on jack studs and support the weight of the wall above the window unit. They are often constructed out of doubled 2x6’s, 2x10’s or 2x12’s.

heat fusion--(welding) method to join PVC frame and/or sash members by heating the cut ends, squeezing them together, and allowing the assembly to cool.

heat treating--the process where glass or aluminum extrusions are heated and cooled to make these materials harder and stronger.

hermetically sealed unit--an insulating glass unit that is sealed against moisture. The unit is made up of two lites of glass, separated by a roll-formed metal spacer tube (at the full perimeter) which contains a moisture and/or solvent absorbing material. The unit is then completely sealed, creating a moisture free air space.

hollow extrusion--an extrusion having an enclosed cavity within it.

hopper--A window unit in which the top of the sash swings inward.

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I

IGCC--Insulating Glass Certification Council - directs a certification program of periodic accelerated laboratory testing and unannounced plant inspections to ensure sealed insulating glass performance is in conformance with ASTM E 774-88.

inside snap trim--used in retrofit work to cover the inside gap between the new window and the existing opening.

insolation--Incident solar radiation -- the total radiation striking an exposed surface.

Insulating Glass Unit (IGU)--A combination of two or more panes of glass with sealed air space(s) between panes -- dualpanes, tripanes, and quadpanes. Also referred to as thermopanes or sealed units.

Insulating glass(IG)--two pieces of glass spaced apart and hermetically sealed to form a unit with an air space between. Heat transmission through this type of glass may be as low as half that without such an air space. A combination of two or more panes of glass with a hermetically sealed air space between the panes of glass. This space may or may not be filled with an inert gas, such as argon. Two sheets of glass bonded together in a unit to enclose a captive air space. Units are constructed with a metal spacer inside the outer perimeter. The outer edges are sealed. Spacers contain desiccant material for absorbing and holding any remaining moisture in the air space.

insulation--A material with high resistance (high R-value or low U-value) that is used to retard heat flow. Air, Argon, or Krypton gas spaces between panes of glass provide insulation in IGUs.

integral mullion--a frame member trapped within the master frame to separate vents or fixed glass.

interior glazed--glass glazed from the interior of the building.

interlock--a design feature which enables sash to become engaged with one another when closed

internal gain--The heat produced in the interior of a dwelling from the operation of lights, appliances, etc.

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J

jack stud--Vertical framing members, generally 2x4’s, which form the inside of the window or door rough opening. They support the header and run down to the sole plate.

jamb--The main vertical members forming the sides of a window or door frame. Side jambs are the vertical pieces of a window frame. The head jamb is the horizontal piece across the top. The vertical member of a window frame.

jamb liner--In a modern double-hung window, the track installed inside the jambs on which the window sashes slide. Vinyl or metal covering applied to the side jambs of double hung and single hung windows. They are generally formed to include an integral balance system and stops for the exterior and interior surfaces of the sash.
 

K

keeper--a hardware device into which a window locking latch engages for security. The receiving portion of a lock that interlocks with the lock arm. It’s mounted to the upper sash check rail on a double hung or single hung window and the inside surface of the sash stile on a casement window.

kitchen bay--A small bay window used above counter-height in kitchens -- allows for a wider view and an inside sill for herbs and flowers.

knocked down (kd)--Product components that are shipped unassembled, e.g., the frame for a sliding glass door.

krypton--An inert, colorless gas used instead of air in sealed spaces between panes of glass in insulating glass units to increase insulation. Provides greater insulation than Argon.
 

L

laminated glass--A type of safety glass comprised of two pieces of glass with a clear vinyl interlay.

left or right--location information, always outside looking in, that can be used to specify direction, e.g., "the operating sash slides to the right."

lift--A handle or grip installed or routed into the bottom rail of the lower sash of a double hung or single hung window

light--A separately framed piece of glass in a window or door. A traditional double-hung window, for instance, often has several lights divided by muntins in each sash. Such windows are described as six-over-six, eight-over-one, twelve-over-twelve, etc., to indicate the number of lights in each sash. Sometimes spelled 'lite.' A single (monolithic) glass pane or piece.

low e or low-emissivity (low-e) glass--a transparent coating applied to a glass surface to separate long wave (heat) energy and short wave (light) energy. The long wave is reflected back to the heat source. The short wave is allowed to pass through the coating. A special type of glass having a transparent material fused into its surface which acts as a thermal mirror.

low e glass--Low Emissivity glass with a transparent coating which acts as a thermal mirror -- used to increase a window's insulating value, block or increase heat flow, and reduce fading.

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M

marine glazing--a u-channel of soft PVC which is wrapped around the edge of the glass, cushioning the glass against the aluminum or vinyl. This process allows for unrestricted expansion and contraction and watertightness

masonry opening--The space in a masonry wall left open for windows or door. The opening in a masonry wall to accept a window or door unit, the same as a rough opening in a frame wall. The header (or lintel) in a masonry opening is usually a steel beam.

meeting rail--the part of a hung window where the two sash meet and create a weather barrier.

mill finish--the original finish produced on aluminum by extruding.

mortise--A slot or rectangular cavity cut into a piece of wood to receive another part.

mortise-and-tenon--A strong wood joint made by fitting together a mortise in one board and a matching projecting member (tenon) in the other.

mullion--Applies to any short or light bar, either vertical or horizontal, used to separate glass in a sash into multiple lights. Also called a windowpane divider or a grille.

mullion cover--an extrusion that joins panning perimeter legs that extend over existing mullions.

muntin--extrusions in the sash which are exterior (outside of the glass exterior face), internal (in the insulating glass airspace), or true (dividing the glass) which appear to or actually divide the glass into smaller lites

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N

nailing fin--A vinyl or metal flange integrated into (or attached to) the perimeter of a window frame for installation onto the rough opening’s header, jack studs and rough sill. A continuous nailing fin may surround the frame as with an all-vinyl window or a nailing fin may be affixed to the head and side jambs as with a vinyl clad window frame.

neoprene--a synthetic rubber having physical properties closely resembling those of natural rubber. It has extremely good weather and temperature resistance, both heat and cold, with ultraviolet stability.

nite latch--hardware which, when extended, restricts the sash opening to a predetermined dimension.

O

obscure glass--mainly used for decoration, diffusion, or privacy. The pattern is rolled into the hot glass during glass manufacturing.

operating unit--A window or door that opens -- also referred to as a vent unit or operator.

operator--A metal arm and gear device which allows for easy opening and closing of projecting windows; e.g. casement and awning windows.

oriel window--a window with unequal sash.

orientation--The compass direction that a structure faces. To optimize heat-gain, the major facade of a building should face South (a variation as much as 30 degrees east or west of south will not seriously affect performance).

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P

palladian window--A large, arch-top window flanked by smaller windows on each side.

pane--A framed sheet of glass.

panel--Usually refers to the separate panel or panels in a door frame.

panel--Either an opaque glazing material or the operating portion of a sliding glass door.

panning--a set of extrusions which are fastened to a new window to cover the exterior perimeter of an existing opening in a retrofit application

parting stop--In a double-hung window, a strip of wood applied to the jamb to separate the sash.

passive solar--A solar heating system which operates on natural thermal processes, and that uses no external mechanical power to move the collected heat. Generally, the building's structure itself forms the solar system.

patio doors--Sliding glass doors, often used for access to a deck or terrace.

picture frame casing--The use of casing on all four sides of the interior of a window. The stool and apron at the sill are replaced with casing.

picture window--A large stationary (non-ventilating) window which is designed for a maximum view without obstruction.

picture windows--A type of window using only fixed units -- best for a clear view and energy efficiency.

pleated shade--A shade of folded fabric which can be installed like regular shades or between the panes of glass of a window.

prime frame--a window frame which has an extended perimeter leg 1" back from the window exterior plane, which becomes a nailing fin for new construction installation.

psf--pounds per square foot - a measurement of air pressure used in window testing, e.g., 1.56 psf (25 mph) or 6.24 psf (50 mph).

PVC--Poly Vinyl Chloride - in rigid frame/sash members, and in flexible gaskets.

pyrolytic coating--A special coating "sprayed" directly onto glass while it is still in a molten state, resulting in a permanently embedded surface coating.

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Q

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R

r value--a measurement of heat resistance (the higher, the better). R value = the number 1 divided by the U value. Resistance to thermal transfer or heat flow. Higher R-value numbers indicate greater insulating value.

radiation--The direct process of heat transfer through space by means of electromagnetic waves. Energy in the form of rays of light is transferred from body to body without heating the intermediate air.

rail--The top and bottom horizontal members of the framework of a window sash or door panel. a horizontal sash member.

receptor--framing system consisting of two snap-together extrusions used to contain a window frame head and jambs in a masonry type opening. It allows for deflection and inconsistencies in the openings.

reflectance back.--A measurement in percentage of the visible light reflected back into a room. For ease of seeing to the outside, a lower rating is better

reflected radiation--Solar radiation that strikes an exposed surface (like a window) after being reflected from the ground, trees, buildings, snow, etc. Reflected radiation can provide a significant amount of heat when vertical windows are used.

reflective glass--glass with metallic coatings applied onto or into the glass surface to reduce solar radiant energy and visible light transmission

relative heat gain--A measurement of the total heat gain through glazing for a specific set of conditions.

relative humidity--Humidity expressed as a percentage of the maximum possible humidity at a given temperature.

removable grilles--Ornamental or simulated muntins and bars designed to provide a divided light appearance. Generally made of wood, they are applied to the inside of the sash against the glass surface for easy removal.

rough opening--The opening built into a frame wall to receive a window or door unit. It is formed with a header along the top that’s supported by jack studs on each side. The rough sill at the bottom is supported by cripples. A rough opening is generally greater in width and height than the window or door unit. The framed opening in a wall into which a window or door unit is to be installed.

rough sill--The horizontal framing piece, usually a 2x4, which forms the bottom of the rough opening. It is toe-nailed into the jack studs and supported by cripples.

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S

sash--The inner frame which holds glass in operable and fixed window units.

sash--the operating portion of a hung or horizontal sliding window. A single assembly of stiles and rails made into a frame for holding glass. The framework holding the glass in a window unit. It’s composed of two stiles (sides) and two rails (top and bottom).

sash balance--A coiled spring or spiral system integrated into the jamb liners to allow double hung or single hung sashes to open and close. They also allow the sashes to remain open in varied positions..

sash cord--In double-hung windows, the rope or chain which attaches the sash to the counter balance.

sash lift--A protruding handle screwed to the inside bottom rail of the lower sash on a double-hung window. Available on all Pella double-hung windows.

sash lock--Generally, a cam-action lock applied to the check rails of a double/single hung window, or sliding window to pull the check rails tightly together. They are also applied to the open edges of a projecting window to seal the sash tightly to the frame. Sash locks provide security and weatherability.

sash stop--cover in jamb track that reduces sash travel on hung windows.

sash weights--In older double-hung windows, the concealed cast-iron weights which are used to counterbalance the sash.

screw boss--a continuous screw track in an extrusion. The track is designed to accept a specific diameter sheet metal screw to provide a secure means of fastening extrusions without the use of reinforcement.

sealed unit--See Insulating Glass Unit.

seat board--A flat board cut to fit the contour of a bow or bay window that’s installed between the sills and the flat wall surface. They provide a seat or shelf space.

SGCC--Safety Glazing Certification Council - administers tempered glass testing and certification program.

shading coefficient--The measure of how well glazing blocks solar heat gain relative to 1/8" clear glass under the same conditions. The lower the shading coefficient, the better the unit blocks solar heat.

shims--Wood wedges used to secure the window or door unit in the rough or masonry opening in a square, level and plumb position during and after installation.

side lights--Tall, narrow, fixed or operating sash on either or both sides of a door to light an entryway or vestibule. Narrow fixed units mulled or joined to door units to give a more open appearance. Tall, narrow, fixed or operating sash on either or both sides of a door to light an entryway or vestibule.

sidelight--A narrow fixed unit joined to one or more doors, providing a more open appearance.

sill--The bottom of a door or window frame.

sill--The main horizontal member forming the bottom of the frame of a window or door. The horizontal piece that forms the bottom of a window frame. It is generally slanted down to the outside to shed standing water. The lower horizontal member of a window frame.

sill angle--extrusion that, when applied below the window, permits the gap below the window to be closed after window installation.

sill course--The row of bricks, cement blocks or stones laid horizontally at the bottom of a masonry opening.

simulated divided light--A method of constructing windows in which muntins are affixed to the inside and outside of a panel of insulating glass to simulate the look of true divided light.

single glazing--Use of single panes of glass in a window. Not as energy-efficient as double glazing.

single strength glass--(SSB) 3/32" thickness.

single-hung--A double-hung type of window in which the top sash is fixed or inoperable

skylight--A special window set into a roof to provide natural light.

slider--A type of window with one fixed sash, and one that slides sideways -- good where outside clearance is limited.

sliding window--A window with two or more sashes that slide horizontally past each other within the frame.

solar gain--The absorption of heat from the sun -- the amount of solar radiation (measured in BTUs) received by a surface.

solar heat gain coefficient--The fraction of incident solar radiation entering a home through the windows -- the lower the number, the better the window is at blocking heat gain. See Solar Shield.

solar shield--The shielding or blockage of the sun's heat.

solar tempered house--A dwelling that obtains a large part of its heat from the sun.

solar transmittance--The percentage of total solar energy that glazing transmits through a window -- a standard clear dualpane has a solar transmittance of 71%.

sole plate--The bottom horizontal piece in a frame wall, usually single or double 2x4’s. The wall is nailed into the deck or rough floor through the sole plate.

solid extrusion--an extruded shape other than a hollow or a semi-hollow extruded shape. Less costly to produce compared to semi or hollow shapes.

Sound Transmission Class (STC)--A rating measure for the ability of glazing to block out sound from outside sources. The higher the STC rating the better the sound blockage (and the quieter the home).

spandrel glass--glass mounted between floors of a building. It is usually made opaque to hide building components.

specialty--A type of window with distinct shapes, such as octagons, round-tops, ellipticals, rakeheads -- virtually any shape can be custom manufactured.

sputtered coating--A coating deposited on glass or film atom-by-atom in a precise process inside a vacuum chamber.

STC--Sound Transmission Class - describes acoustical control for interior panels, and, even though inadequate, is currently the only criteria for exterior windows. The higher the number, the better the product is at resisting typical sound frequencies excluding airplane and train noises.

stile--a vertical sash member. The vertical side pieces of a window sash or door panel. The main vertical members of the framework of a sash or door panel.

stool--An interior trim piece on a window which extends the sill and acts as a narrow shelf. The interior horizontal trim piece at the bottom of the window frame. The shelf-like piece that projects into the room.

stop--A molding used to hold, position or separate window parts.

subsill--refers to extrusions positioned to collect water leakage through mullions and products and drain it to the exterior. Used where high performance water resistance is required and for windows joined with mullions. It runs continuously across the opening width and can be spliced together to cover wide openings. The ends are sealed with end dams.

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T

tempered glass--Glass that has been heat-treated to become more than three times stronger -- also known as safety glass because it breaks into small pebbles rather than jagged shards. It is used in sliding glass doors and windows susceptible to impact or breakage.

tempered glass--Glass manufactured to withstand greater than normal forces on its surface. When it breaks, it shatters into small pieces to reduce hazard. Glass that has first been cut to size, then heated to a very high temperature and then rapidly brought back to room temperature. It will withstand severe punishment from a blunt object; however, any pointed object will break the glass instantly and the glass will crumble into many, very small pieces.

tenon--A rectangular projection cut out of a piece of wood for insertion into a mortise.

thermal break--An air space or insulating material which prevents the direct coupling of a cold surface to a heated surface.

thermal break--an element of low conductivity (polyurethane) placed between elements of higher conductivity (aluminum) to reduce the flow of heat and cold.

thermal break--The addition of a thermal insulating material between two thermally conductive materials.

thermal bridge--The direct coupling of a cold surface to a heated surface, allowing heat transfer via conduction.

thermal mass--the amount of heat storage capacity available in a given material or assembly. Thermal mass in a home (tile floors, stone fireplace, etc.) will absorb excess heat generated during the day and store it until ambient temperature drops.

thermal radiation--Electromagnetic radiation emitted by a warm body -- the sun.

thermal resistance--The ability of a material to impede the flow of heat. See R-value.

thermosetting --baking the organic paint finish on aluminum to endure a tight bond and long life.

tinted glass--Glass other than clear, with a color cast or tint. Typically tinted glass absorbs and blocks heat, and reduces visible light transmittance.

tinted glass--glass of special formulation to produce light reducing and/or heat absorbing glass products (bronze, gray or green).

total unit --A basis for measurement, evaluation and performance comparison of different glazing configurations, established by a formula combining R-values of the frame area, edge of glass area, and center of glass area.

translucent--A glazing such as frosted glass, which transmits electromagnetic radiation (light) but causes scattering so that a clear image cannot be seen.

transom-- A window installed above another window or door.

transom--A small window that fits over the top of a door or window, primarily for additional light and aesthetic value.

transparent--Clear glazing which transmits light without diffusion, and which can be seen through clearly.

tripane--An insulating glass unit consisting of three panes of glass with two internal air spaces.

true divided light--A term which refers to windows in which multiple individual panes of glass or lights are assembled in the sash using muntins.

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U

U value--a measurement of heat transmission. The U value of a window is measured by the number of BTU's that will pass through each square foot of area per degree of temperature difference from one side of the window to the other (the lower, the better). U value = the number 1 divided by the R value

ultraviolet radiation (uv)--Electromagnetic radiation from the sun, with wavelengths shorter than visible light -- UV-caused fading of furnishings, artwork, etc. after prolonged exposure to direct sunlight can be a problem. Classical measurement of UV transmittance (300 -- 380 nm) is generally used to indicate fading potential and to compare UV-blocking performance of various glazing types.

unison lock--A casement locking system which secures the window at two locking points by operation of one handle.

united inches--the sum total of one window width and one window height expressed in inches.

u-value--Rate of heat flow-value through the complete heat barrier, from room air to outside air. The lower the U-value, the better the insulating value

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V

vent--the operating portion of a window that swings or projects in or out.

vent unit--A window or door that opens, to provide ventilation.

vent unit--A window or door unit that opens or operates.

vinyl--A plastic material used by some window for cladding or entire window units.

visible light transmittance--The percentage of visible light (380 to 760 nanometers) that is transmitted through glazing. Visible light transmittance is affected by special coatings and the number of panes of glass or film in an insulating glass unit.

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W

warm edge spacers--Insulating spacers used to seal panes of glass in the manufacture of insulated glass units -- edge conductivity is lessened for improved window energy performance and reduced condensation problems.

wave length selective--"Intelligent" coatings such as Low E2 and Heat Mirror allow for glazing combinations to permit selective gain or shielding of the sun's heat, while letting in visible light.

weather stripping--Thin sections of material used to prevent air leakage around operable windows and doors -- usually foam gasketing, metal strips, or vinyl.

weatherstripping--A material or device used to seal the openings, gaps or cracks of venting window and door units to prevent water and air infiltration.

wedge glazing--a flexible, continuous gasket that ensures a high compression seal between the glass and glazing bead by applying pressure.

weep slot--an opening cut into a window sill and/or sash rail to allow water to drain to the exterior.

wind load--the amount of pressure exerted by the wind on a window or door generally expressed in pounds per square foot (psf).

windload--Force exerted on a surface by moving air.

window size--always expressed as width first, then height

windowpane divider--See muntin.  

wire glass--1/4" clear or obscure glass having a layer of diamond or square pattern wire mesh embedded in the glass lite.

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X

"XO" sliding window--"O" indicates fixed sash = left sash slides and right sash is fixed.

"XX" sliding window--"X" indicates moving sash = both sash operate.

Y

Z