Window and door glossary

During the process of purchasing windows you're going to come across some terms that you may have never heard before. To help we've collected some of them together and provided an explanation for each.

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

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

Arch window: 4 sided unit with a curve at the top

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: A window hinged at the top the sash swings outward from 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

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.

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

Casement window: A window hinged on either side the sash opens horizontally opposite the hinge.

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

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 to protect it from the elements

Clear opening area: 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

Condensation Resistance: Condensation Resistance (CR) measures how well a window resists the formation of interior condensation. CR is expressed as a number between 1 and 100. The higher the number, the more resistant to condensation formation.  Condensation Resistance ratings are determined under specific laboratory conditions. Actual condensation performance is a function of temperature, humidity and air movement as well as other uncontrolled, site specific factors.

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 surfaces when exposed to humidity).

Conversion kit: Retrofit kit to add tilting capability to 1968 and newer Andersen® Perma-Shield® Narroline® windows

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

Design Pressure: Pressure (measured in pounds per square foot-psf) required by building codes to meet windload requirements. Our product "PG" -Performance Grade rating is used to determine compliance.

Direct glazed/ direct set: Glass is directly glazed into frame; stationary unit

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

Dowel joint: A corner joint created by precisely boring matching holes into a door rail and style and joining them together with a dowel pin

Drip cap: One piece aluminum or vinyl cover installed above windows/doors that directs water away from the top of the unit

Dual pane/Double pane glass: Two panes of uncoated (non-Low-E) glass with an air-filled cavity (not argon-blend gas-filled)

Egress window: A venting window large enough to be used as an emergency exit. Check local codes for egress requirements in your area.

ENERGY STAR®: A government-backed program to help consumers identify energy efficient products.

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

Extruded aluminum: Aluminum that is shaped by running it through a die, typically more durable than roll-formed material

Fenestration: Refers to any opening in a structure filled with a window, door or skylight.

Fibrex® material: Exclusive to Andersen, its a composite of wood fiber and PVC polymer thats 2x stronger than vinyl.

Fixed/Stationary: Non-venting or non-operable

Flashing: Water resistant material that directs water away from your windows

Flexiframe®: Andersen brand name for fixed geometric windows shapes (octagon, pentagon, trapezoid)

Folding door: Door unit with multiple hinging panels that can be folded together to create an large, unobstructed opening

Foot lock: Auxiliary lock used on gliding doors to secure the operating panel to the sill

Frame: Outer structure of a window or door that holds the sash or panel in position

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/Muntins/Dividers/Bars/Grids: Components used to simulate individual pieces of glass within a sash/panel

Grilles-Between-the-Glass (GBG's)/Finelight™: Grille bars that are placed between the glass panes; allows for easy cleaning

Gusset plate: Metal plate attached to a window or door to strengthen a window or door joint

Half insect screen: Insect screen that only covers the lower sash area of a double-hung windows

Handing: Opening direction of hinging windows and doors; direction is determined by location of hinge on unit as viewed from exterior

Head board/Seat board: Stain grade wood shaped to the angles of a bay or bow window that form the finished upper and lower interior surfaces

Header: Heavy beam extended across the top of the rough opening to divert the weight of the wall or roof around the window

Impact Resistant glass: Laminated glass frequently used in hurricane-prone areas for protection from wind-borne debris

Insect screen: A tightly woven mesh attached to a frame; allows outside air ventilation while keeping insects out

Insert window: A new window unit intended to be installed inside the frame pocket of an existing window

Insulating glass unit: Two or more glass panes that are sealed together to increase energy efficiency

Jalousie window: Louvered window with multiple horizontal glass sections that rotate open or closed

Jamb: Window or door frame members that form the top and sides of a unit

Jamb clips: Metal brackets used to secure a unit to the rough opening from the interior

Jamb liner: Interior frame cover surface where the sash slide on double-hung window

J-channel: Receiver components that surrounds a window intended to hide the seam between the window and siding

Joining: Two or more window or door units joined together with mull materials or Andersen’s Easy Connect joining system; joint can run vertically, horizontally or both. 

Keeper: Receiver on a sash that the lock engages

Keyed lock: Patio door lock that enables locking and unlocking from the home's exterior

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

Laminated Veneer Lumber (LVL): Engineered wood consisting of multiple layers of thin wood bonded together

Lift: Handle on the bottom of a double hung window that makes it easier to raise/lower the sash

Light/Lite: Individual glass panes within a window sash or door panel

Lock: Mechanism used to secure windows and doors into a closed position

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

Masonry opening: Opening in a brick, stone or stucco wall where a window or door is installed

Measurement guide: Step-by-step tool to help in determining the dimensions of replacement windows

Meeting stile: Central location on a gliding window or door where the sash/panel overlap

Monolithic glass: Laminated glass that has no air space; used in specific situations such as some coastal applications

Mortise-and-tenon: Strong wood joint made by fitting together a slot (mortise) in one board and the matching projecting member (tenon) on the adjoining board

Mullion: The vertical or horizontal joint between individual window or door units that form a combination

Multi-point lock: Lock that engages the sash or panel in multiple locations; activated by a single motion

Nailing flange / Installation flange: Narrow attachment strip on the window perimeter that typically used to secure the window to the rough opening and provide added protection from water infiltration

NFRC: National Fenestration Rating Council is an non-profit organization that provides for fair, accurate and credible energy performance ratings for windows, doors & skylights.

Obscure glass: Glass with a texture of pattern of various degrees of opacity that limits visibility through a window or door (see also patterned glass)

Operator: Metal arm, gear and handle used to open and close hinged windows

Outdoor/Indoor Transmission Class (OITC): Measurement standard used to indicate the rate of sound transmission between indoors and outdoors (see also STC)

OX / XO: "OX" or XO" are used to identify the opening direction of gliding windows/doors; "X" stands for operating while "O" stands for stationary

Palladian window: Large, arch-top window flanked by smaller windows on each side

Panel: Refers to the rail, stile and glass assembly on a door; similar to a window sash

Panning kerf: Narrow groove on the exterior outer frame edge of a unit typically used to accept trim or aluminum coil stock

Parting stop: A narrow frame molding that holds a sash or panel in position

PassiveSun™ glass: Andersen brand name for a glass type ideal for situations where solar heat gain is desired, typically in passive solar building designs.

Passive panel/sash: Panel/sash that will open only after active panel/sash is opened

Patterned glass: Glass than lets in light while obscuring vision (see also Obscure glass)

Performance Grade (PG): An industry rating for a unit that has been tested for air, water, structural and force entry performance. Used to determine compliance with code required design pressures.

Perma-Shield®: Andersen brand name for low-maintenance exterior cladding

Plinth block: Decorative wood block typically found at the top corners of the unit that creates a transition from vertical to horizontal interior trim

Pocket door: A door panel that can be concealed by a wall; panels slide into wall

Pre-finished: Factory painted or stained unit that is ready for installation; no finish coat required

Pultrusion: Strong, stiff composite material, in profile form, made from polymeric resin and glass fiber. Also used to refer to the process for producing these profiles

Push-out casement: A casement with no crank handle; window is opened by releasing sash lock and pushing the sash outward

Rail: Horizontal components of a window sash or door panel framework

Reinforced mull: Mull that uses a structural material (wood, aluminum, steel, LVL) to provide a stronger joint

Removable Interior grille: Interior grille that can be readily removed for cleaning

Reverse Cottage/Oriel window: Double-hung window where the upper sash is larger than the bottom sash

Rough opening: Opening in a wall for the installation of a window or door. The rough opening is larger than the actual unit to allow for shimming and insulating.

Sash: Rail, stile and glass components joined together the form the venting capability of a window

Sash glazed /Sash set: Fixed window with a separate sash and frame intended to replicate the look of nearby venting windows

Seal: A compressible surface that inhibits air and water passage

Segmented arch: Multiple arch windows mulled horizontally to provide a single continuous arch

Shim: A wedge often made of wood used to plumb and/or level a window or door in the rough opening

Sidelight: Tall, narrow unit placed alongside a window or door

Sill: Horizontal member that forms the bottom of a window or door frame

Sill Nose: Traditional exterior trim component that attaches underneath and extends out beyond the sill

Simulated divided light: Use of interior and exterior grille with no spacer between the glass panes; used to simulate the look of a window with multiple glass lites

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

SmartSun™ glass: Andersen brand of a glass option that reduces solar heating but allows high visible light transmission

Solar Heat Gain Coefficient (SHGC): A measurement of the sun's heat energy that passes through the window/door. The lower the value the less heat gain thru the product.

Sound Transmission Class (STC): Rating system used to measure how much sound is transferred through windows/doors (see also OITC)

Springline™ windows: Round top picture windows

Stile: The vertical components of a window sash or door panel

Stool: Flat, interior trim member located at the sill of a window or door, typically extending into the room and horizontally beyond the extension jambs

Stop: A trim member attached to the window or door intended to hold, position or separate components

Stormwatch® protection: An Andersen brand name for a series of upgrades you can specify to meet increased code performance in coastal areas. Check your local codes for performance requirements in your area

Sun glass: Tinted glass that reduces heat gain

Sustainable Forest Initiative (SFI): Forest certification standard dedicated to promoting sustainable forest management

Tempered glass: Safety glass that is stronger than annealed glass and breaks into small pieces

Threshold: Decorative wood component used as a transition door sill to the interior flooring

Top hung insect screen: Insect screen used on patio door and are secured from the top; results in smoother operation

Transition block: A decorative wood piece used to cover the joint between extension jambs or casings

Transom: Window positioned directly above another window/door

Triple pane: Glass construction consisting of three distinct layers of glass and two air-spaces

True Divided Light (TDL): Windows and doors in which multiple smaller glass lites are framed in a single sash or panel

TruScene® insect screens: Unique to Andersen this patented micro-fine stainless steel mesh provides 50% more clarity than typical Andersen insect screen cloth

U.S. Green Building Council (USGBC): Non-profit trade organization that promotes sustainability in how buildings are designed, built and operated

U-Factor: Commonly used measurement of heat transmission through a window/door. The lower the U-Factor, the better the insulating value.

Unobstructed glass opening: Visible glass area

UV protection: Percentage of Ultra-Violet (UV) transmission from the sun's energy. The lower the number, the potential for reduced fabric fading. (See Damage Function)

Vapor barrier: Watertight material used to prevent moisture migration around windows and doors

Vent Limiter: Device that restricts window operation and cannot be disengaged without tools or special effort.

Venting unit: Window or door that opens; operates

Vinyl: Polyvinyl chloride (PVC) material that is very durable and resistant to corrosion.

Visible light transmission: The fraction of the light allowed to enter through a window

Weatherstrip: Compressible material designed to seal the sash or panel to the frame

Weep holes: Small holes placed on the exterior of a window or door that allows for water drainage

Window Opening Control Device (WOCD): Device intended to restrict the opening dimension of a window when first activated to less than 4 inches, but can be disengaged to allow full opening of the sash for escape and rescue, but reengages when the sash is closed such that the sash will open to a less than 4 inch dimension when opened again.