Window Screen Glossary

Acorn Latch - are a plastic or aluminum type of window screen hardware. These turn clips screw onto the window screen frame to help hold the screen in your window.

Acorn Pivots - screw to the corner of a window screen frame and allows the screen to pivot open and shut.

Acorn Pointers - are another form of window screen hardware that rivot onto a window screen frame and turn to hold frame in the window. Acorn pointers are usually made of a hard vinyl material.

Active Panel - the primary operating door panel.

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

Aluminum Surround - the aluminum frame around a screen or energy panel.

Apron - a piece of casing or decorative trim installed against the wall immediately beneath the stool of a window.

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

Argon Gas - a colorless and odorless gas used to fill the airspace between insulating Low E glass. The addition of argon greatly increases the insulating performance of the Low E glass.

Assembly - Single units of windows or doors mulled together.

Astragal - a moulding applied to one stile of a French Door, Sliding French Door or French Casemaster window unit which the other door panel or window sash strikes. Usually head and footbolt devices will be found on the astragal side. Astragal: Center post of a double door attached to the fixed or inactive door panel

Authentic Divided Lites (ADL) - Also known as True Divided Lite. Permanent stationary muntins and bars separate the glass in a window or door sash to give the sash two or more lites of glass.

Awning Window Unit - a combination of frame and sash, hinged at the top of the vertical jambs which allows the unit to pivot from the top with the sash opening to the exterior of the building.

Balancer - Counter-weight mechanism to assist raising or lowering of a double-hung or single hung sash

Balances - a block and tackle system used in the jamb liner of double hung or single hung units.

Bail Loop Latches - is a popular window screen hardware used to hold bottom of a window screen snug into the window frame. The ball head screw is inserted in the inner side of the window sill. They come in two styles:

  • Slip-On Latch - the bail latch is pushed onto the bottom of the screen frame and the latch hook is slipped over the screw. Fits Aluminum Screen Frame up to 7/16" Thick.
  • Spline Channel Latch - the ball head screw is inserted on the inner side of the sill and the latch hook is placed over the screw.

Bars - a narrow rabbeted, horizontal or vertical sash or door member in an authentic divided lite unit, extending from rail to rail or stile to stile along the total length or width of the glass opening.

Bay Windows - A series of windows installed in a bay which is two flanker units and a center sash; a bay may be an arc or a polygon; when a bay is or closely approaches an arc, the window is termed a bow. See Bow Windows.

Blindstop - The frame member on a double hung window located between the jambs and the casing. The blindstop forms a rabbet that supports either a storm sash or screen.

Bow Windows - a series of adjoining window units, installed on a radius.

Brick Mould Casing BMC - an exterior moulding of window and door frames that abuts the exterior facing material of the structure. The casing serves as the boundary moulding for brick or other siding material and also helps to form a rabbet for screens and/or storm sash or a combination door.

Bug Flap - is a rubber seal that provides a flexible seal against all sorts of bugs and insects. The flexible flap on the strip rubs against the sliding glass doors so that insects cannot penetrate the gap between the screen and glass doors. against insects. The flexible flap on the strip rubs against the sliding glass doors so that insects cannot penetrate the gap between the screen and glass doors. Available in widths of 1 1/2" and 2 1/4" and available in black only.

Cam Lock - a lever operated lock which is used to prevent intrusion through the sash. Cam locks and keepers were installed on the jambs and stiles of older Casemasters and awnings.

Cam Pivot - a zinc pivot pin attached to the top and bottom sash stiles of double hung units (bottom sash on single hung units). Cam pivots rest on the clutch system of the balance tube assembly which allow opening and closing of the sash.

Casement window - Unit with hinged sash that opens to the side; allows top to bottom ventilation

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

Center Cross Bar - is usually made of aluminum and is in the center or off-center position of a window screen to assist in the overall stablity of the window screen. Cross bars are optional but are recommended especially in window or adverse weather environments.

Check rail - Located on double-hung windows where the bottom sash and top sash meet and the lock/keeper is mounted

Cladding - Low maintenance covering or coating attached to the unit exterior

Clear opening - 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

Combination Storm - a wood or aluminum storm sash with self-storing screen and operating glass panels. Available for double hungs, gliders and wood swinging doors, these panels are removable.

Combination unit - a storm window and insect screen contained in a single frame

Combination Window - a wood or clad wood frame storm sash with self-storing screen. Bottom glass panels such as those installed on a double hung unit operate by moving the plungers in and sliding the glass panel up to the desired position. Side glass panels such as those installed on gliders slide to the left or right to the desired position. All inserts are removable from the inside.

Condensation - Water that collects as droplets on the glass/sash/panel interior or exterior under certain conditions (typically cold services 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 - a window with unequal sash, top and bottom. Double-hung window where the upper sash is shorter than the bottom sash

Custom Window Screen - a window screen custom made based on irregular or custom built windows. Custom window screens can be made within 1/16" of an inch of the dimensions provided by the customer in many different frame and screen options.

Daylight Opening (DLO) - The width and the height of the visible glass.

Depth of the Jamb - The point where the exterior casing ends to the point where the interior casing begins. On clad units, the point from the backside of the nailing fin to the interior of the frame.

Direct Glaze - Refers to a window with no sash. The glass is glazed directly into the frame and is stationary.

Double Hung - Double hung windows have two movable sash which operate vertically. Double hung sash are held in an open position with the use of coil spring block and tackle balancing devices.

Double Hung Tilt Pac - a specially designed, made-to-order, package which includes everything needed to replace double hung sash and hardware in an existing frame without changing the frame. This product has the same tilt feature as the Marvin double hung.

Drip Cap - one piece formed aluminum or vinyl unit which is installed at the top of windows and doors that allows water to run off the casing of the unit instead of seeping around the casing and into the unit. The drip cap’s goal is to direct water away from the top of the unit\

Egress window - a venting window required by buiding codes for emergency escape and rescue, which are typcially required in bedrooms and which are required to meet certain minimum opening dimensions.

Electric Operator - an electrically operated device which will open Casemasters or awnings units by using a switch. This is used in lieu of a roto gear crank or pole crank.

Energy Panel (EP) - Formerly called an RDG - removable double glazing, is a piece of glass annealed or tempered, and finished on the edges by a surround. EPs are applied to windows or doors and rest on the glazing stop. EPs offer the homeowner added energy efficiency.

ENERGY STAR® - a federal government-backed program to help consumers identify energy efficient products.

Escutcheon - a decorative door handle plate attached to the stile directly behind the handle(s). Generally square or rectangular shaped.

Espagnolette - tilt-turn hardware which houses the gear mechanism for the Tilt-Turn, inswinging casement and hopper handles.

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 dye, typically more durable than roll-formed material

Extrusion - an article or product of vinyl or metal-made by the process of extruding. Extrusions include vinyl sill and head jamb tracks, vinyl jamb liners and aluminum cladding used on the exterior of clad units.

Field Measurement Guide - a form that is filled out prior to ordering the Clad Magnum Double Hung Replacement System with Panning to ensure the correct sized unit is assembled at the factory.

Finger-Joint - a series of fingers machined into the ends of two pieces of lumber to be joined together. They are then held firmly in position by adhesive. Finger jointed wood is very strong and has a lesser chance of warping than does a clear piece of wood the same length.

Flanker - a former term used to describe a side or lateral part. Also previously used to describe a 3-wide picture unit or bay. See two-wide entry.

Flashing - a water resistant material that directs water to a drainage plane or to the exterior surface of a building.

Flat Casing - a flat, surfaced on four sides, pieces of pine of various widths and thicknesses for trimming door and window openings. The casing serves as the boundary moulding for siding material and also helps to form a rabbet for screens and/or storm sash or combination doors.

Footbolt - a locking rod device installed vertically in the stile or astragal of a door or screen which when activated secures the panel or screen in a stationary position.

Frame - the stationary portion of a window that encloses either the glass (direct glaze) or the sash (operating or stationary) and consists of the head jamb (top), sill (bottom), sub-sill, side jambs, jamb extension, brick mould or flat casing, and blindstop.

Frame Expander - a flat aluminum extrusion used in conjunction with the 90 degree frame expander to provide a flat casing appearance for clad units.

Glazing Bead - Strips of profiled wood or vinyl used to hold the glass in position in the sash. Wood glazing bead is attached to the rails and stiles of the sash using staples, small nails or vinyl barbs. A vinyl bead is held in place by extruded barbs positioned in the kerf. Aluminum caps may be used over the vinyl bead in some cases.

Glazing Tape - a two sided adhesive tape placed between the glass rabbet and the glass and/or the glazing bead and glass of some unit types.

Glider - horizontal operating units which have one sash fixed while the other glides open and shut horizontally.

Gliding window/sliding window - Window with two sash, where one sash slides horizontally past the other

Grilles - Removable wood dividers made to simulate authentic divided lites. Grilles are often rectangular or diamond shaped and are easily removed for cleaning purposes. Grilles can be purchased for nearly all Marvin products.

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

Half insect screen - Insect screen that covers the opening area of the operating sash in hung and gliding windows

Handing - a term used to describe the right or left hand operation of a window or door.

Head Jamb - the top member of a frame.

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

Headbolt - a locking rod device installed vertically in the stile or astragal of a door or screen which when activated secures the door in a stationary position.

Historical - a term used to define a window or door product meeting the requirements of historical renovation standards.

Inactive Panel - secondary operating door panel.

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

Inswing French Door - a French door with panels that swing to the inside. One, two, three and four panel units available as stationary or operating.

Inswinging Casement - a non-tilting version of the Magnum Tilt-Turn.

Interior Casing - the casing trim used on the interior perimeter of the window or door. Generally supplied by others except in the case of round top casing which is factory supplied.

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

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

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 Extension - a jamb-like member, usually surfaced on four sides, which increases or extends the depth of the exterior or interior window or door frame; jamb extensions imply a larger depth than "wood jamb liners."

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

Jamb Extension - a jamb-like member, usually surfaced on four sides, which increases or extends the depth of the exterior or interior window or door frame; jamb extensions imply a larger depth than "wood jamb liners."

Jamb Liner - thin strips of wood attached to the head jamb, side jambs and sill to accommodate various wall thicknesses. Common jamb depths are: 4 9/16", 4 13/16", 5 1/16" and 5 3/16".

Keyed Cylinder Lock - a lock providing an exterior entry and locking convenience.

Laminated Glass - is a glass compossed of two sheets of glass fused together with a sheet of transparent plastic between the sheets. When broken, laminated glass will generally not leave the opening.

Laminating - a method of gluing strips of thin clear wood to the lengthwise surfaces of finger jointed material to provide the appearance of clear stock.

Lever Lock - a lever handle and lever arm operator available as an option on awning units.

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

Lockset - a complete door lock system comprised of the lock mechanism together with knobs, keys, plates, strikes and other accessories.

Loop Latches - see "Bail Loops Latches" definition above.

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

Mortise and Tenoning - the system by which Marvin assembles authentic divided lite units, a projecting tenon on either the muntins or bars fit snugly into a mortise in either a bar, stile or rail. Strong wood joint made by fitting together a slot (mortise) in one board and the matching projecting member (tenon) on the adjoining board

Mulling - the act of attaching two or more window or door units together. The joint is then finished with a mullion center cap or mull trim.

Mullion - the vertical member of a sash, window or door frame between openings in a multiple opening frame.

  • SPACE MULL: Two or more units mulled together with a space left between the units. The jamb extension surrounds the entire unit.
  • STUD POCKET: Two or more units mulled together with a space between the units. The jamb extension surrounds each unit separately, providing space for a support member between the units.

Mullion Cover - a clad cover for space mull usage on the Clad Magnum Double Hung Replacement System with Panning. It covers a range from 3" minimum to 10" maximum.

Mullion Expander - an aluminum extrusion designed specifically for the Clad Magnum Double Hung Replacement System with Panning to allow the existing panning to be expanded to a wider width to accommodate a larger rough opening.

Mullion Reinforcement - the 3/8" mullion reinforcement is designed to be used on wood or clad multiple Casemaster, awning and direct glaze assemblies to improve structural performance.

Multi-Lock Hardware - an adjustable lock system used on the French Casemaster to ensure a tight seal of the sash frame components. It also provides a secure locking system.

Multi-Point Locking System - a line of standard or optional multiple point locking mechanisms installed on the operative panel(s)/ sash of various Marvin products to enhance security and performance.

Muntins (or "munt") - a short "bar," horizontal or vertical, extending from a bar to a stile or rail or another bar.

Nailing Fin - a factory installed vinyl strip that is inserted into a kerf in the frame of clad units. Nailing fin installation is the standard method used for installing clad units.

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

Non-Keyed Cylinder - a handle without a keyed cylinder. The door cannot be locked from the exterior.

Obscure Glass - a glass formed by running molten glass through special rollers. These rollers have a pattern on them causing the glass to become patterned and thus obscure.

One-Wide (1W) - the current term used to describe one frame with single or multiple sash or panels.

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

OX - The letters identify the operation of window or door units as viewed from the exterior. The letter O stands for stationary while the letter X stands for operating.

Palladian window - a large, arch-top window flanked by smaller windows on each side. Custom window screens can be made for palladian windows.

Panel - either the stationary or operator wood frame with glass used on Marvin door products.

Panning - a term used to describe the aluminum covering extrusion components (i.e. jambs, sill and head jamb) used for the Clad Magnum Double Hung Replacement System with Panning.

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

Parts: The following is an interactive image that will show you some of the critical parts of a custom window screen:

Part Stop - a strip of wood with weather-stripping attached which prevents air and water infiltration. Part stops are commonly found at the head jamb of a double hung unit.

Pet Screen - a type of window screen that is made with heavy grade screen to withstand pets running into or scratching the window or door screen.

Pitch - a term used to describe the angle of a roof. For example: A 4-12 pitch indicates that the roof rises 4" vertically for each 12" horizontally.

Plinth Block - a decorative wood block placed between the vertical casing and the top casing of a unit to provide an elegant interior casing profile.

plunger-example.jpgPlungers - are another optional window screen type of hardware. Plunger bolts usually come in sets of two and includes a bolt, cap and spring. The spring loaded plunger attached to the window screen pops into a hole in the window frame to hold the screen in place.

Pole Crank - an aluminum extension pole used to open or close roof windows or awnings which would be inaccessible because of their height.

Polygon - a high level term used to describe triangles, trapezoids, pentagons, hexagons and octagons.

Prime - the first coat of paint in an application that consists of two or more coats; also refers to the paint used for such an initial coat - primer.

Pull Tabs - are a form of window screen hardware that holds the window screen to the window frame. Pull tabs are easy to use and are one of the more popular hardware choices on custom window screens.

R-Value - the resistance a material has to heat flow. Higher numbers indicate greater insulating capabilities.

Rabbet - a groove along or near the edge of a piece of wood.

Radius - the length of an imaginary line from the center point of a circle to the arc or circumference of a circle.

Rails - the cross or horizontal members of the framework of a sash, door or other panel assembly.

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

Relief Kerf - Kerfs machined into the frame parts of a unit. Relief kerfs inhibit warping.

Retro-Sizing - refers to units which are sized for replacement purposes.

Rolled Aluminum - a term used to describe aluminum profiles for screen and energy panel surrounds which are fabricated by the use of a roller or series of rollers to produce a desired profile. All other Marvin profiles are fashioned by the extrusion method.

Roller Cams - the adjustable roller devices of the Multi-Lock hardware installed on the sash of the French Casemaster unit. When adjusted properly with an Allen wrench, they ensure a tight seal between the sash and frame members.

Rose - a circular cover plate attached to the stile directly behind a knob or door handle. May be plain or have a decorative design embossed into the cover.

Roto-Gear - a term used to describe the steel drive worm, gears and crank device used for opening awnings and Casemasters.

Rough Opening - the opening in the wall where a window or door unit is to be installed. Openings are larger than the size of the unit to allow room for insulation and to shim the unit square.

Round Top - generally a semicircle window which is mulled to the top of another window or door, thus forming the round top appearance. There are full round tops, separated round tops, ellipticals, transoms, inverted corners, ovals and Gothic heads, etc. Round tops can be used separately or combined with other units to create a seemingly endless selection.

Round Top Tilt-Turn - a round top sash version of a Magnum Tilt--Turn unit.

Sash - the operating and/or stationary portion of the window unit that is separate from the actual frame. The sash consists of the following parts:

  • Sash Limiter - an optional metal device which attaches to a Casemaster sill and bottom rail which limits the sash to a specified opening -5, 10, 15 or 20 degrees.
  • Sash Lock - a locking device which holds a window shut, such as a lock at the check rails of a double hung unit. Larger units utilize two locks.
  • Sash Opening (SO) - the opening between wood frame members for both height and width (disregarding any jamb hardware tracks). This measurement is used predominantly when measuring an opening for the Double Hung Tilt Pac.
  • Sash Retainer Plate - a nylon retainer plate used on double hung and Magnum Double Hung sash to secure the bottom sash.

Screen - a close-mesh or tightly woven screen material of metal or fiberglass attached to an aluminum or wood surround that allows outside air ventilation while keeping the insects out. Screens inhibit entry of insects, yet permit light, air and vision. Window screens can also block the sun's heat with solar guard screen material and protect the inside of the house from direct sunlight.

Screen Clips - is another window screen hardware option that are used to hold the window screen in the existing window frame. Screen clips are attached by either screws or rivots depending on the screen clip style. All are made of either high strength plastic or high strength aluminum.

Screen Door Tracking - tracking usually is available in heavy-duty extruded aluminum. Screen door top track is available for single tracking. Double tracking is for french door applications. Several sizes and colors are available.

Screen OM (outside measurement) - tThe width and the height of a screen including wood or metal surrounds.

Screen Spline - is a serrated, hollow core vinyl used for securing window screens into a window frame. Spline is pliable and works easily into the screen frame channels to hold the screen mesh securely. Spline comes in a variety of diameters and will fit into almost any screen frame available on the market today.

Screen Wicket - Plastic wickets are 10-1/8 inches wide x 6-1/8 inches tall. Wickets are used to allow easy access to casement or awning window operators. You can install screen material to match your window screen material.

Seal - a compressible surface that inhibits air and water passage

Segmented arch - multiple arch windows mulled horizontally to provide a single continuous arch

Sequential Locking System - an exclusive Marvin design used on Casemasters for locking the sash to the frame. The action is sequential where the lower lock activates first moving the sash to the weatherstrip; the top then engages to snug the sash to the frame.

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

Side Jamb = the side (vertical) member of a frame.

Sidelite - a stationary glass panel mulled to or installed next to a door.

Sill - the horizontal member forming the bottom of a window or exterior door frame; the lowest member of the frame of a structure, resting on the foundation and supporting the frame. Horizontal member that forms the bottom of a window or door frame

Sill-Horn - the extension of the lip of a window sill to the outside edge of the casing.

Single Hung - a window very similar to a double-hung window, except that the top sash is stationary or non-operable.

Sliding French Door - a sliding door utilizing French door style panels.

Slope - the measure of the tilt of a line; rise over run.

Snubber - an interlocking metal bracket attached at the center of the hinge side of a Casemaster sash and frame with a call number height of 40" or more and both sides of an Awning sash and frame with a call number height of 48" or more. It pulls the sash tightly against the frame weather-strip to maximize performance.

Spacer - used to separate the two pieces of glass in an insulating glass panel.

Square Foot - for measuring the area of a unit. RO width (in inches) x RO height (in inches) divided by 144 equals the area in square feet of a unit.

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) - a rating system used to measure how much sound is transferred through windows/doors

Stabilizer Arm - an optional piece of hardware for the Tilt-Turn window which is attached to the header and top rail corner drive on the handle side to limit the travel of the sash when operated in the tilt mode. It is automatically disengaged when the sash is swung in the turn mode.

Starburst - a semi-elliptical area, the lower center is the point where the dividing spokes meet and radiate outward. May be constructed of glazed sash, removable grilles, ADL or SDL.

Stationary - a non-operating sash, panel or unit.

Stationary Sash Bracket - a 90 degree L bracket used to secure stationary Casemaster and awning sash to the frame. The sash can be removed for replacement by removing the wood stops and bracket screws.

Stiles - the upright or vertical perimeter pieces of a sash, panel or screen.

Stool - a horizontal trim member that laps the window sill above the apron and extends beyond the interior casing. See apron entry.

Storm Sash - a wood framed assembly containing non-removable glass. The storm sash is removed during the summer and replaced with a wood framed screen.

Structural Masonry Brackets - an installation bracket used with multiple high/wide window units or large doors for added structural support. The brackets are also used to attach the unit in the rough opening in lieu of nailing through the casing, thus eliminating unsightly nail holes.

Sub-Sill - the supplemental member of a frame used under most awning and casement units as an additional sill with the primary purpose being to hold multiple units together at the sill.

Sunburst - a semi-elliptical area, the lower center of which contains a sun-like figure with sun rays radiating therefrom. May be constructed of glazed sash, removable grilles, ADL or SDL.

Surround - an attractive, protective trim which is secured to an energy panel by an adhesive or vinyl barb to give the glass panel a safe finished edge. Also the aluminum framework for most standard screens.

Tempered Glass - float glass panels heated and then cooled rapidly in a controlled environment. This process makes the glass several times stronger than regular glass. It also makes it safer because when broken it yields small pebble-like fragments.

Template - a pattern of a window unit from which dimensions and measurements can be determined. Round Tops require templates for replacement units.

Tension Springs - is another optional window screen hardware that helps keep screens held tightly within a window frame channel. Depending on the application you need there are three types of tension springs. All three are installed differently but all will still help hold in your Window Screens tightly and secure within the channel of your window frame.

Three-Wide (3W) - current term referring to any product or unit when three frames (i.e. separate jambs) are mulled together as a multiple unit.

Tilt-Pac - a specially designed made-to-order package which includes everything needed to replace double hung sash and hardware in an existing frame without changing the frame. This product has the same tilt feature as the Marvin double hung.

Top hung insect screen - an insect screen used on patio door units that are secured from the top; results in smoother operation

Transom - a window above a window or door. Transoms can be either stationary or operating.

Trimline - a wood or clad patio door having two or three glass panels; one panel operates. Formerly known as a Wood Retro (WR) or Clad Retro (CR) door. The door features a multi-point locking system.

Turn Button - a vinyl or aluminum button and screw. Buttons are used to secure wood combinations, storm sash and wood screens to the exterior casing or energy panels to the sash or door panel.

Two-Wide (2W) - current term referring to any product or unit when two frames (i.e. separate jambs) are mulled together as a multiple unit.

U-Factor - a measure of total heat flow through a window or door barrier from room air to outside air. Lower numbers indicate greater insulating capabilities. Commonly used measurement of heat transmission through a window/door. The lower the U-Factor, the better the insulating value.

Ultrex - a pultruded composite material made of polyester resin and glass fibers. This superior material is now being used in many Marvin products.

Unit - One single product such as a one wide casemaster.

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.

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

Vinyl Glazing Bead - a vinyl extrusion used on clad units which serves the same purpose as a wood glazing bead for wood units.

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) - a 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.

Weather-Stripping - a strip of resilient material designed to seal the sash and frame members in order to reduce air and water infiltration.

Wire Glass - glass with wire embedded into the glass when the glass is still in a molten state. This prevents the glass from falling out of the sash if it should break.

XO - the letters OX or XO identify the operation of window or door units as viewed from the exterior. The letter O stands for stationary while the letter X stands for operating.

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