Glossary of Terms

Window & door terms you need to know.

​Want to know the difference between R-value and U-factor? What do pultrusion and extrusion mean? We want you to be informed when shopping for your windows and doors. Find definitions to common terms used on this site and in the windows and doors industry below.

AAMA Silver – A labeling program sponsored by AAMA certifying the thermal performance of windows and doors as reported as U-factor (or U-value), SHGC and VT.

Acrylic – Thermoplastic glazing material.

Active –This is an operating panel (X) as viewed from the exterior.

Aerogel – A microporous, transparent silicate foam currently under development for potential use as a glazing cavity fill material, offering very high thermal performance.

Air infiltration – The amount of air leaking in and out of a building through cracks in walls, windows and doors.

Airspacer – A component placed at the perimeter of an insulating glass unit to separate the two lites of glass.

ANSI – American National Standards Institute, a clearinghouse organization for all types of standards and product specifications

Annealed glass – Standard float glass.

Annealed PVC – An added process in the cellular process to aid in stability of the product.

Arch-top – One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as circle-heads, circle-tops and round-tops.

Argon – An inert, nontoxic gas used in insulating glass to reduce heat transfer.

ASHRAE – American Society of Heating, Refrigeration and Air Conditioning Engineers, a national association that establishes standards for building energy performance.

Astragal – The center post between two swinging doors.

ASTM International – Formerly the American Society for Testing and Materials, a trade association that establishes material standards (including glass) and test methods. It has also produced a window installation standard.

Awning – A window with sash swinging outward from the bottom.

Backband – The millwork around the outside edge of the window casing, usually used when the casing consists of flat boards.

Backbedding – A material or compound used to seal the glass to a window sash.

Balance – A mechanical device (normally spring loaded) used in single- and double-hung windows as a means of counterbalancing the weight of the sash during opening and closing.

Basic – NO mulling, NO casing, NO nail fin/drip cap, but ready for field/shop mulling or field/shop applied casings.

Bay – A combination of window units that projects to the exterior. Usually features a large center unit with two flanking units at a 30° or 45° angle to the wall.

BETEC – Building Environment and Thermal Envelope Council. Part of the National Institute of Building Sciences, an organization representing government and industry, BETEC is involved in communicating government policy and influencing standards development within the industry.

Bi-hinge – Windsor’s term for two panel doors where both panels can open, hinged on the side, with one active panel and one passive panel.

BOCA – Building Officials and Code Administrators. One of the three model code groups in the U.S. now merging to form the International Code Council.

Boot glazed – A glazing method using a vinyl boot to surround the glass. Also called commercial glazing.

Bottom rail – The bottom horizontal member of a window sash or door panel.

Bow – A combination window that projects to the exterior.

Box bay – A combination of window units that project to the exterior. Usually features a large center unit with two flanking units at a 90° angle to the wall.

Breather tube – A tube placed through the air spacer and seal of insulating glass that allows the unit to accommodate changes in pressure between time and location of manufacture and time and location of installation, where it is sealed. Usually used to accommodate changes in altitude between plant and job site.

Brickmould – A type of external casing for windows and doors.

Caming – The metal used in the construction of decorative glass panels. Usually zinc or brass, it is also applied to single glass lites to create a decorative glass look.

Casement – A window with sash cranking outward, to the right or left.

Casing – The exposed moulding or profile around a window or door, on either the inside or outside, to cover the space between the window frame or door jamb and the wall.

Caulking – A compound for filling joints and sealing cracks to prevent leakage of water and air.

Cellular PVC – An extruded polyvinyl chloride material used in window and door components and trim. Unlike rigid (or hollow) vinyl, it features a foam or cell-structure inside. It can often be nailed, sawn and fabricated like wood.

Cellulosic composite – Generally, a material combining an organic material, such as wood fiber, extruded with a plastic.

Celuka PVC – A process to add to the hardness of the product.

Chain of Custody (CoC) – The process of tracking wood that derives from a certified forest through the manufacturing and distribution channels. Most commonly referenced certification systems are FSC and SFI CoC. Facilities that are CoC have the processes in place to track certified wood from the moment it enters the facility to the moment it leaves. Builders who use CoC wood can earn points toward the certification of a home through the LEED or NAHB standards.

Check rail – The bottom rail on the upper sash and the upper rail of the lower sash of a double-hung window unit, where the lock is mounted. Also referred to as a meeting rail.

Circle-top – One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as arch-tops, circle-heads and round-tops.

Cladding – The material placed on the exterior of wood frame and sash components to provide ease of maintenance. Common cladding materials include vinyl and extruded or roll-formed aluminum.

Clear IG – Two panes of glass sealed to form a dead air space between the two panes of glass.

Clerestory – A window in the upper part of a high-ceilinged room that admits light to the center of the room.

Combination door – A screen or storm door used in combination with a primary door. Storm windows also are referred to as combination windows

Composite – A term used for window or door components, which consist of two or more materials, such as wood and plastic. The term also is used for windows and doors which combine two or more materials in the frame or sash construction, such as a product with a wood interior and a vinyl or aluminum exterior.

Condensation – Water vapor from the air deposited on any cold surface that has a temperature below the dew point. Sometimes a problem on cold (and poorly insulated) window glass or framing that is exposed to humid indoor air.

Condensation Resistance (CR) – A measurement of how well a product resists the formation of condensation on the roomside of the unit. CR is expressed as a number between 1 and 100. The higher the number, the better a product is able to resist condensation. CR is an optional rating.

Corner cleaner – A machine that removes the bead of excess material formed in welding vinyl window corners.

Cottage double hung – A double hung window in which the top sash is shorter than the bottom sash.

CRF – Condensation Resistance Factor. A rating of a window's ability to resist condensation. The higher the CRF, the less likely condensation is to occur.

CRM – Customer Relationship Management. A computerized system for tracking all contacts with customers and prospects.

Dade County – Florida County, including Miami, which has set numerous standards and requirements for hurricane-resistant windows and doors.

Daylight opening – The amount of visual area seen through a piece of glass.

Desiccant – A material used to absorb moisture from within the sealed airspace of an insulating glass unit.

Design pressure (DP) – A measurement of the structural performance of a window or door. Usually specified as one-and-half times greater than necessary based on expected building wind and weather conditions.

Direct glaze – A method of glazing a piece of glass directly to a frame using a stop glazed method. This method is commonly used in direct sets and radius units; NO sash involved.

Direct set – A geometric shape that incorporates all straight legs.

Divided lites – Separately framed pieces or panes of glass. A double-hung window, for instance, often has several lites divided by muntins in each sash. These designs are often referred to as six-over-six, eight-over-one, etc… to indicate the number of lites in each sash. Designs simulating the appearance of separately-framed panes of glass are often referred to as SDLs or simulated divided lites. Designs using actual separate pieces of glass are sometimes referred to as TDLs or true divided lites.

Dormer – An area which protrudes from the roof of a house, generally featuring one or more windows.

Double glazing – Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits. May or may not refer to an insulating glass unit.

Double hung window – A window featuring two operable sash that move vertically in the frame.

Double-strength glass – Glass between 0.115 and 0.133 inches thick.

Drip cap – Moulding placed on top of the header brickmould or casing of a window frame.

Dual Low-E – A glazing option which combines Cardinal LoE 366 soft coat on the inside surface of the exterior pane with Pilkington Energy Advantage™ Low-E hard coat on the inside surface of the interior pane. The Pilkington Energy Advantage™ Low-E hard coat is a very thin pyrolytic coating that is integral to the interior glass surface. This hard, durable, low emissivity coating gives the product improved thermal insulation performance compared to clear insulated glass or standard Low-E insulated glass.

Edge effect – Heat transfer at the edge of an insulating glass unit due to the thermal properties of spacers and sealants.

Egress window – A window designed to be large enough for a firefighter to climb in or a person to climb out in an emergency. U.S. building codes require each bedroom of a home to have an emergency exit window, with minimum sizes specified. Generally requires 20" width and 24" height opening and 5.7 sq. ft. opening.

Electrochromic glazing – Glass or other glazing material that can be switched from clear to opaque electronically.

Elliptical – A double radius unit with tight radius on the end and a flowing/low arc radius on top with the height less than half the width.

Energy Star® – A program sponsored by the U.S. Department of Energy which establishes minimum performance standards for windows to be recognized as energy efficient. Three different sets of standards for U-value and solar heat gain have been established for three different climate zones in the U.S.

ERP – Enterprise Resource Planning, a computerized system that is used to manage all aspects of a company’s operation.

EuroWindoor - A consortium of European window, door and curtainwall industry associations involved in the development of common EU standards.

Extended quarter – Height greater than the width.

Extension jamb – A trim component that extends from the interior of the window frame to the interior wall.

Extruded aluminum – A heavier, thicker aluminum product used to clad the exterior of wood windows and doors.

Extrusion – The process in which a heated material is forced through a die, used to produce aluminum, vinyl (PYC), and other profiles or components used in the production of windows and doors. Term also is used to refer to the profiles or lineals manufactured by this process and used to make window and door components.

Fanlight – A half-circle window over a door or window with radiating bars.

Fenestration – Originally, an architectural term for the arrangement of windows, doors and other glazed areas in a wall. Has evolved to become a standard industry term for windows, doors, skylights and other glazed building openings. From the Latin word, "fenestra," meaning window.

Finger-joint – A toothed joint used to combine two pieces of wood end-to-end.

Fixed lite – A non-venting or non-operable window.

Fixed panel – A non-operable door usually combined with operable door unit.

Flashing – A thin strip of metal or other material that diverts water away from a window, door or skylight.

Float glass – Glass produced by a process in which the ribbon is floated across a bath of molten tin. The vast majority of flat glass is now produced using this method. The terms "plate" glass and "sheet" glass refer to older manufacturing methods still in limited use.

Flush door – A door produced using two skins or faces separated by a stile-and-rail frame construction at the perimeter. Flush doors may be produced with a hollow core or solid core.

Fogging – A deposit or film left on an interior surface of a sealed insulating glass unit due to extreme conditions or failed seals.

Frame size – The actual box size of the unit, outside to outside dimensions (not including brick mould). This is an important dimension used with special size Windsor wood windows.

French doors – A a pair of hinged doors that open from the middle. Also incorporates wider stile and rail components around the glass than typical glazed doors.

French slider – A sliding patio door using wider stiles and rails to replicate a French door look.

FSC – Forest Stewardship Council. The only globally recognized certification system that guarantees products have been made from environmentally and socially sustainable managed forests. FSC certifies forests and also the manufacturing and distribution chains, which would be CoC. The use of FSC CoC can earn builders points through the LEED and NAHB home certification program.

Full Round – A circle unit with equal width and height.

Fusion-weld – A type of corner construction, used with vinyl and other types of windows and doors, in which a small amount of material on the ends of two pieces are melted or softened, then pushed together to form a single piece. Also referred to as a welded corner.

Glass size – The actual glass size of a unit. This is a common callout for most standard size Windsor wood products (except doors).

Glazing – The glass (and other materials) in a window or door. Also, the act or process of fitting a unit with glass.

Glazing stop – A component of the sash or door panel that holds the glass in place. Also, the referral that holds the glass in place.

Glider – A window with a movable sash that slides horizontally. Also referred to as a horizontal sliding window.

Gothic – A radius unit that generally comes to a point at the top or a grille design that has a radius look without making a full circle.

Grille – A term referring to window pane dividers or muntins. It may be a type of assembly fitted to the interior of the window or door unit that can be detached for cleaning. Can be fitted inside the sealed insulating glass unit, when it is referred to as a grid.

Half round – A stock or special half round unit where the height is half the width.

Hallmark – A window and door certification program sponsored by WDMA.

Handing and Hinging – Always viewed from the exterior.

Hard-coat glass – A glass product that is coated during the manufacturing process at the molten glass stage. Also known as a pyrolytic coating, this type of coating offers a surface that is generally as durable as an ordinary glass surface, and therefore requires no special handling and does not need to be used in an insulating glass unit. The other type of glass coating is a sputter-coat, which is applied in a secondary process. Sometimes referred to as a soft-coat, these types of coatings generally require some additional care in handling and fabrication and must be used within an insulating glass unit.

Head – The main horizontal frame member at the top of a window or door.

Header – The horizontal framing member placed over the rough opening of a window or door to prevent the weight of wall or roof from resting on the frame. Also known as a lintel.

Heat gain – The transfer of heat from outside to inside by means of conduction, convection and radiation through all surfaces of a house.

Heat loss – The transfer of heat from inside to outside by means of conduction, convection and radiation through all surfaces of a house.

Hollow-core door – A flush door constructed with two skins or door faces separated by stiles and rails at the perimeter. Generally, a honeycomb type support is used inside the door between the two faces.

Hopper – A window with a sash that swings inward from the top.

Horizontal slider – A window with a movable sash that slides horizontally. Also referred to as a gliding window.

IBC – International Building Code. Published by the International Code Council, the IBC primarily covers nonresidential construction.

ICBO – International Council of Building Officials. One of the three model code groups in the U.S., now merging to form the International Code Council.

IECC – International Energy Conservation Code. Published by the International Code Council, the IEEC sets forth compliance methods for energy-efficient construction of both residential and nonresidential construction.

Inactive – A fixed panel (O) as viewed from exterior.

Inner bar (simulated spacer channel) – The spacer bar between the glass in a Windsor Divided Lite (WDL) unit (this is not GBG, or grille between the glass).

Inner grille – Windsor’s term for GBG, or grille between the glass.

In-sash – Glass glazed in a sash before being installed in a frame.

Insulating glass (IG) – Two or more lites of glass with a hermetically-sealed airspace between the them. The sealed space may contain air or be filled with an inert gas, such as argon.

In-swing – Panels that swing to the interior, as viewed from exterior.

IRC – International Residential Code. Published by the International Code Council, the IRC primarily covers low-rise residential construction.

Jalousie – A window made up of horizontally mounted glass louvers or slats that abut each other tightly when closed and rotate outward when cranked open.

Jamb – The main vertical members forming the sides of a window or door frame, also refers to the horizontal member at the top of the window frame, as in head jamb and side jamb.

Jamb depth – The width of a window or door from the interior to the exterior of the frame to meet construction wall thickness.

Jambliner – The track installed inside the jambs of a double-hung window, on which the window sash slide.

J-channel – Installed or built-in to the side of a window or door, this channel is designed to accommodate the ends of siding pieces to provide a finished appearance.

Knocked down (KD) – An unassembled window or door.

Laminated glass – Two or more sheets of glass with an inner layer of transparent plastic to which the glass adheres if broken. Used for enhanced safety and security, as well as sound reduction.

LEED – The Leadership in Energy and Environmental Design. A benchmark system, established by the USGBC, which certifies green homes and buildings through an accumulation of points earned through the implementation of green practices. Buildings can earn LEED. Silver, Gold or Platinum levels of certification.

Lineal – A standard length profile or shape which is cut and processed to make window and door components.

Lintel – A structural component or beam above a window or door opening that supports the wall above. Also referred to as a header.

Lite – A piece of glass. In windows and doors, lite refers to separately framed panes of glass (as well as designs simulating the look of separately framed pieces of glass). Sometimes spelled "light."

Lite cut – The layout of a grille pattern.

Low-emissivity (Low-E or LoE) glass – A coated glass product that reflects heat.

Managed forests – Forests that have had a number of management techniques applied to them, including prescribed burning, thinning, harvesting and planting. Well-managed forests provide clean air and water, homes for wildlife, beautiful scenery, places for recreation and more than 5,000 products we use every day. Poorly-managed forests are often unhealthy and unproductive due to overcrowding, disease, insects and competition for light, water and nutrients. Poorly-managed forests also account for a large number of wildfires. Managed forests are compatible with FSC and SFI.

Marine glazed – A glazing method using a vinyl boot to surround the glass. Also called commercial glazing.

Masonry clip – An accessory clip that is used to install windows into brick.

Masonry opening – Area in a masonry wall left open for windows or doors.

MDF – Medium-density fiberboard. A wood fiber composite used in a variety of window, door and millwork applications.

MEC – Model Energy Code. Established by Energy Policy Act of 1992 to serve as a baseline for state energy codes. To be succeeded by International Energy Conservation Code (IECC).

Mechanical window – A term for a product, usually vinyl, in which the corners are assembled using screws or other fastening mechanisms, as opposed to a welded corner construction. Also referred to as a mechanically-fastened window.

Mullion – A component used to structurally join two window or door units.

Multi-point lock – A locking system, operated with one handle, which secures a window or door at two or more locking points.

Muntin – A profile or moulding, either vertical or horizontal, used to separate glass in a sash into multiple lites. Generally refers to components used to construct divided lite grids or grilles simulating a divided lite look.

Nail fin – An accessory component or integral extension of a window or patio door frame which generally laps over the conventional stud construction and through which nails are driven to secure the frame in place.

Narrow slider – A sliding patio door using narrow stiles and rails for maximum daylight opening.

NFRC – National Fenestration Rating Council. A third party certification agency that developed and operates a uniform national rating system for the energy performance of fenestration products.

NRFC rating system – The backbone of the rating system is a procedure for determining the heat transmittance (U-value) of a product. Additional rating systems developed by the NRFC measure Solar Heat Gain Coefficient (SHGC), Visible Transmittance (VT), Air Leakage (AL) and Condensation Resistance.

Nonrenewable resources – A limited supply of resources that can’t be replaced once they’ve been extracted and used. These resources are being recycled, such as aluminum and plastic.

NWWDA – National Wood Window and Door Association. A trade organization that has established many standards related to wood window and door products. It is now the Window and Door Manufacturers Association (WDMA).

One-step distributor – A wholesale company that buys building products from a manufacturer and sells them to builders, contractors and homeowners is referred to as a one-step distributor. A wholesaler that buys building products from the manufacturer and sells them to lumberyards and home centers, which in turn sell to builders, contractors and homeowners, is referred to as a two-step distributor.

Oriel – A window style in which the upper sash is larger than the lower sash.

Out-swing – Panels swing to the exterior as viewed from exterior.

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

Panel – A component, usually wood, mounted within stile and rail members of doors. Also used to refer to the entire door.

Panning – In replacement window work, the outside aluminum trim that can extend around the perimeter of the window opening; used to cover up the old window material.

Parting stop – A narrow moulding, either integral or applied, that holds a sash or panel in position in a frame.

Perimeter grille – A grille with a perimeter frame. Also known as a surround grille.

Picture window – A large, non-operating window that is usually longer than it is wide and provides a panoramic view.

Pivot window – A unit with a sash that swings open or shut by revolving on pivots at either side of the sash or at top and bottom.

Plate glass – Flat glass produced by grinding and polishing to create parallel plane surfaces affording excellent vision. Although the term is still used commonly, most window glass is now produced using the float process. See float glass.

Polycarbonate – A plastic material used for glazing.

Polyvinyl Butyral (PVB) – A plastic material used as the interlayer in the construction of some types of laminated glass.

Polyvinyl chloride (PVC) – An extruded material used for window and door framing

Post-consumer recycled material – Any household or commercial product that has served its original, intended use and then gets recycled. 

Pre-consumer recycled material – Industrial manufacturing scrap that gets recycled.

Pre-hanger – A company that buys doors, framing, hardware, glass lites and other components, and prepares (or pre-hangs) the unit for installation.

Primary active panel – The active panel (X) of a bi-hinge door.

Prime window – A primary window, as opposed to a storm or combination unit added on.

Primed window – An optional factory finish making units ready to accept finish coat(s).

Projected window – A window in which the sash opens on hinges or pivots. Refers to casements, awnings and hoppers.

Pultrusion – The process used to produce fiberglass composite profiles or components used for the production of windows and doors. Term also is generally used to refer to the composite profiles or lineals cut and processed to make window and door components.

Pyrolytic glass – A glass product that is coated, usually to provide low-emissivity or solar control benefits, during the manufacturing process at the molten glass stage. Commonly referred to as a hard coat, this type of coating offers a surface that is generally as durable as an ordinary glass surface, and therefore requires no special handling and does not need to be used in an insulating glass unit. The other type of glass coating is a sputter-coat, which is applied in a secondary process. Sometimes referred to as a soft-coat, these types of coatings generally require some additional care in handling and fabrication and must be used within an insulating glass unit.

Quarter round – A stock or special quarter round unit where the height and width are equal.

Radiation – The transfer of heat in the form of electromagnetic waves from one separate surface to another. Low-E glass is designed to reduce this type of heat transfer by reflecting electromagnetic waves.

Radio frequency (RF) – Technology used with bar code scanners and other input devices in plant and warehouse tracking systems.

Rail – The horizontal member of the framework of a window sash or door.

Reflective glass – Glass coated to reflect visible light and solar radiation striking the surface of the glass.

RESFEN – A computer program designed to calculate energy use based on window selection in residential buildings.

Rolled-form aluminum – A cladding method using a rolled type method of bending. Mainly used in sash cladding.

Roof window – An operable unit similar to a skylight placed in the sloping surface of a roof.

Rough opening – A framed opening in a wall into which a window or door unit is to be installed.

Round top – One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as arch-tops, circle-tops, and circle-heads.

Round-top picture – A true half round with extended legs.

R-value – Resistance to thermal transfer or heat flow. Higher R-value numbers indicate greater insulating value. R-value is frequently used by the insulation industry and is the reciprocal of U-value, a value more generally used in the window industry.

Safety glass – A strengthened or reinforced glass that is less subject to breakage or splintering and less likely to cause injury if broken. Law requires glass in doors to be some type of safety glazing product, such as tempered or laminated glass.

Sash – An assembly of stiles and rails (vertical and horizontal members) made into a frame for holding glass.

Sash cord – Rope or chain in double hung windows that attaches the sash to the counterbalance.

Sash lift – A protruding or recessed handle on the inside bottom rail of the lower sash on a double or single hung window.

Sash size/Sash opening – The actual sash opening of a unit. A generic or common callout for double hung products.

Sash weights – The concealed cast iron weights used to counterbalance the sash of older double hung windows.

SBCCI – Southern Building Code Congress International. One of the three model code groups in the U.S. now merging to form the International Code Council.

Secondary active panel – This is the passive panel (X) of a bi-hinge door.

Segment top (seg-top) picture – A segment radius unit with legs of same dimensions.

Segment top (seg-top) quarter – A segment radius unit with different dimensions for the legs.

Self-cleaning glass – Glass that is coated with a thin transparent layer of titanium dioxide. This coating acts to clean the window in two stages, using two distinct properties: photocatalysis and hydrophilicity. In sunlight, photocatalysis causes the coating to chemically break down organic dirt adsorbed onto the window. When the glass is wet by rain or other water, hydrophilicity reduces contact angles to very low values, causing the water to form a thin layer rather than droplets, and this layer washes dirt away.

Sequential locking system – A type of multi-point locking system used on casement windows. Lower locks engage and partially close sash before upper locks engage.

Set-up – A unit complete with all mulling and casings applied, ready to install in rough opening.

SFI – Sustainable Forest Initiative. An initiative dedicated to improving sustainable forest management in the United States and Canada. SFI certifies forests and also the manufacturing and distribution chains, which would be CoC. The use of SFI CoC wood can earn homes points through the NAHB program. 

Shading coefficient (SC) – A measure of a window's ability to transmit solar heat, relative to that ability for a single pane of clear glass. The lower a unit's shading coefficient, the less solar heat it transmits, and the greater its shading ability. This method of measurement is being phased out in favor of the solar heat gain coefficient (SHGC).

Sheet glass – A transparent, flat glass found in older windows, now largely replaced by float glass.

Sidelites – Narrow fixed units mulled or joined to operating door units to give a more open appearance.

Sill – The main horizontal member forming the bottom of the frame of a window or door.

Sill nosing – A double hung part added to the main sill of a unit.

Simulated divided lite (SDLs) – A type of grille or grid design that creates the appearance of a number of smaller panes of glass separated by muntins, but actually uses larger lites of glass with the muntins placed between and/or on the surfaces of the glass layers.

Single glazing – A single lite of glass in a window. Generally not as energy efficient as insulating glass or other forms of double glazing.

Single hung – A window resembling a double hung, or vertically sliding window, with a fixed top sash.

Single-strength glass – Glass with thickness between 0.085 and 0.100 inches.

Skin – A single piece of material used as the face of a door.

Slab – A term for a complete door panel that has not been prepared for installation into a frame.

Smart window – A generic term, sometimes used for windows offering high energy efficiency or windows featuring switchable glass to control solar gain.

Soft-coat glass – A glass product that is coated in a secondary process known as sputter-coating, usually to offer low-emissivity or solar control benefits. The term refers to the fact that these types of coatings generally require some additional care in handling and fabrication and must be used within an insulating glass unit. A hard-coat or pyrolytic glass is coated during the manufacturing process at the molten glass stage. This type of coating offers a surface that is generally as durable as an ordinary glass surface, and therefore requires no special handling and does not need to be used in an insulating glass unit.

Solar control glass – Glass produced with a coating or tint that absorbs or reflects solar energy, thereby reducing solar gain.

Solar heat gain coefficient (SHGC) – A rating, which is now generally replacing shading coefficient, measuring a window's ability to transmit solar heat. It measures both the solar radiation which is directly transmitted, as well as the solar radiation absorbed by the glass and subsequently transmitted. The lower a unit's solar heat gain coefficient, the less solar heat it transmits, and the greater is its shading ability. It is approximately equal to the shading coefficient divided by 1.15. It is expressed as a number without units between 0 and 1.

Solid-core door – A flush door produced with a solid material placed within the door skins.

Sound transmission class (STC) – A rating measuring a window's acoustic properties or its ability to reduce sound transmission. An STC rating is determined by measuring the sound transmission over a selected range of sound frequencies. The higher the number, the less sound transmitted.

Spectrally-selective glass – A coated or tinted glazing with optical properties that are transparent to some wavelengths of energy and reflective to others. Typically, spectrally-selective coatings are designed to allow high levels of visible light or daylight into a building and reflect short-wave and long-wave infrared radiation.

Spread mull – A term used for adding a space between mulls. This dimension is based on width between frames, NOT exterior casing size.

Sputter-coating – A secondary manufactur­ing process in which a thin layer of materials, usually designed to offer low-emissivity or solar control benefits, is applied to glass. Sputter-coatings are commonly referred to as soft-coats, as they generally require some additional care in handling and fabrication and must be used within an insulating glass unit. A hard-coat or pyrolytic glass is coated during the manufacturing process at the molten glass stage. This type of coating offers a surface that is generally as durable as an ordinary glass surface, and therefore requires no special handling and does not need to be used in an insulating glass unit.

Stat/Stationary – Does not move.

Stick grille – A grille without a perimeter.

Stile – The main vertical frame members of a sash or door.

Stile-and-rail door – A traditional type of wood door constructed with vertical stiles and rails with openings filled with raised wood panels or glass.

Stool – An interior trim piece sometimes use to extend a window sill and act as a narrow shelf.

Stop – A moulding used to hold, position or separate window or door parts; the moulding or component on the inside of a window frame against which the window sash rests or closes. Also called a bead, side stop, window stop and parting stop.

Stop glazed – A typical method using a stop with a glazing compound to make the seal.

Stud pocket – A spread mull with field knock out blocks for studs to run between mulled units.

Subsill – A casement part added to the bottom front of a casement to form the slop of sill.

Super window – A generic term for a window with a very low U-value. Typically, it incorporates multiple glazings, low-E coatings, gas fills and an insulating spacer.

Sustainability – One aspect of the green movement that is commonly referenced. This focuses on the responsible use and management of resources, specifically concentrating on the use of renewable resources, rather than finite resources.

Swinging door – Windsor’s term for all swing door options, including singles, bi-hinge, center hinge; one, two and three panel options.

Tempered glass – Glass heat treated to withstand greater than normal forces on its surface. When it breaks, it shatters into small pieces to reduce hazard.

Tenon – A rectangular projection cut out of a piece of wood for insertion into a mortise.

Thermal break – A thermally insulating or low-conductance material used between interior and exterior aluminum (or other conductive material) window and door components.

Tilt window – A single or double hung window with operable sash that can be tilted into a room to allow cleaning of the exterior surface on the inside.

Tints – Gray and bronze available as standard options on clear or Low-E IG.

Transom – A window used over the top of a door or window, primarily for additional light and aesthetic value.

Triple glazing – Use of three panes of glass or plastic with two airspaces between. Generally refers to a sealed insulating unit.

True divided lites (TDLs) – A traditional window construction incorporating smaller panes of glass actually separated by muntins, rather than simulating such an appearance with larger lites of glass and a muntin grid or grille placed between or on the surfaces of the glass layers.

Tubular/Hollow PVC – An extrusion technique used for PVC windows to increase structural strength.

Two-step distributor – An industry term for a wholesale company that buys building products from the manufacturer and sells them to lumberyards and home centers, which in turn sell to builders, contractors, and homeowners. A wholesaler that buys building products from a manufacturer and sells them to builders, contractors, and homeowners is referred to as a one-step distributor.

U-factor – A rate of heat flow-value through a building component, from room air to outside air. Also referred to as U-value. The lower the U-factor, the better the insulating value. U-factor, a rating more generally used in the window industry, is the reciprocal of R-value, a rating commonly used in the insulation industry.

Ultraviolet light (UV) – Invisible rays of solar radiation at the short-wavelength violet end of the spectrum. Ultraviolet rays can cause fading of paint finishes, carpets, and fabrics, as well as deterioration of some materials.

Unit size – The overall dimensions of a window unit, including brick mould, subsill, etc… for primed units. Frame Size and Unit Size are same for Clad Windsor products. 

uPVC – Poly Vinyl Chloride product commonly used in many construction products. The “u” added stands for UNPLASTICIZED or rigid PVC. The “u” does NOT mean UV stabilized; ALL PVC is UV stabilized.

USGBC – United States Green Building Council. A nonprofit organization that promotes green building practices and educates people within the industry on what it means to be green. This organization is comprised of people in different realms of the building industry and has set the benchmark for the LEED home certification program.

Vinyl – A generic term for polyvinyl chloride or PVC, an extruded material used for window and door framing.

Visible Transmittance (VT) – A measurement of how much light comes through a product. VT is expressed as a number between 0 and 1. The higher the VT, the higher the potential for day lighting.

Warm-edge – A type of insulating glass construction using an air spacer offering lower thermal conductance than traditional aluminum spacer. Warm-edge IG units typically offer higher resistance to condensation and an incremental improvement in window energy performance.

WDMA – Window and Door Manufacturers Association. Formerly the National Wood Window and Door Association, this trade organization has established many standards related to wood window and door products.

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.

Weep hole – A small opening in window or sill member through which water may drain to the building exterior.

Weld – A term used for a type of corner construction, used with vinyl and other types of windows and doors, in which a small amount of material at the two pieces are melted or softened, then pushed together to form a single piece. This also is referred to commonly as a fusion-weld.

Wet glazed – A typical method using a stop with a glazing compound to make the seal.

Wildland/urban interface – An area where buildings are bounded by wild or natural areas, which are a particular concern in regions where wildfires are a concern. Some fire and code officials are looking at the establishment of fire-resistance requirements for exterior building products in these "interface" areas.

Windload – The force exerted on a surface by moving air.