Acrylic. An optically clear thermoplastic that has good weather resistance and is more shatter resistant than an equally sized pane of annealed glass. Custom Windows uses acrylics, other thermoplastics and laminated glass when resistance to breakage is a key concern.
Air-leakage or Air Infiltration. This is one of four key measurements on a window’s NFRC label. The lower a window’s air-leakage rating, the more air-tight it is and the less transfer of heat or cold (as well as dust and pollen) through the window. While a common problem with single pane windows, almost any modern insulated window will have excellent air-leakage ratings.
Annealed glass. A sheet of float glass which has not been heat-strengthened or tempered. Most insulated glass units use two sheets of annealed glass as their basis.
Argon. Like Krypton, Argon is an inert, nontoxic gas used to fill the space between the two glass panes of an insulating glass unit in place of air. While Argon has minimal benefit in combating solar heat gain, it improves the insulation of a window against cold winter chill. (See U-Factor)
Awning Window. Window similar to a casement where the sash is hinged at the top and swings out along the bottom edge. (See casement and hopper windows.)
Bay window. An arrangement of three or more individual window units, attached so as to project from the building. The most common arrangement uses two operating windows (flankers) on the side of one or more center windows that are set parallel to the building’s wall.
Bow window. A configuration of multiple windows that that projects from the wall in an arc shape, commonly consisting of five or six units.
Casement. A window sash that swings open on a side hinge, usually to the outside. (See casement and hopper windows. Also see Tilt-Turn Window.)
Caulk. A mastic compound for filling joints and sealing cracks to prevent leakage of water and air, commonly made of silicone, bituminous, acrylic, or rubber-based material. Custom Windows exclusively uses a modified urethane that contains no solvents, has no odor and will not shrink over time.
Condensation. The deposit of water vapor from the air on any surface where one side is significantly colder than the other. Euphemistically called ‘sweating,’ single pane windows and some aluminum frames will ‘sweat’ in Houston’s hot and humid summers. Modern insulated glass panels virtually eliminate sweating regardless of the frame material used. Other potential solutions include adding a Custom Windows’ storm window to a single pane window to significantly reduce condensation.
Conduction. Heat transfer through a solid material by contact of one molecule to the next. Heat flows from a higher-temperature area to a lower-temperature one, i.e. during a Houston summer heat transfers from outside to inside where in a Minneapolis winter the problem is reversed. This is one reason that the right window material and glass is NOT the same for every climate.
Convection. A heat transfer process which, in insulated windows or doors, can occur between the panes of glass. Convection currents occur between the panes when the temperatures of the inside and outside panes of glass differ significantly. This causes the air or gas to circulate between the panes (hot air rises and cold air sinks) and causes ‘energy’ to transfer from the warmer pane to the cooler pane. The greater the difference between the exterior and interior temperature, the more critical convection can be. An inert gas such as Argon reduces convection in windows climates temperatures can vary substantially between inside and out.
Desiccant. An extremely porous crystalline substance used to absorb moisture that is used in the spacers that separate insulated glass panes. It is this desiccant that helps maintain the proper humidity in an insulated unit and keeps it from fogging as long as the spacer’s seal is not breached.
Divided Lite (DL). A window with a number of smaller panes of glass, sometimes known as colonial lites. In older single pane windows these smaller panes are individual pieces of glass held in place by muntins, however these multiple small panes are often a key source of energy loss due to air-leakage. Modern insulated windows mimic this look by using muntin bars (or grids) between the panes of glass or SDL bars on the outside of the glass, but the actual glass panel is one solid unit, virtually eliminating air-infiltration.
Double Pane Glass (Insulated Glass or IG). In general, two thicknesses of glass separated by an air space to improve insulation against heat transfer and/or sound transmission. In factory-made double glazing units, the air between the glass sheets is thoroughly dried or replaced by an inert gas, the space is sealed airtight and a desiccant filled spacer used to eliminate possible condensation and providing superior insulating properties.
Double-hung window. A window in which both the upper and lower halves can be slid up and down.
Double-strength glass. Float glass roughly 1/8” thick. While it is permitted to use thinner single-strength glass in producing windows, Custom Windows uses double-strength glass at minimum in all windows that we produce.
Egress. In relation to windows, one that meets minimum clear opening requirements for escape in case of an emergency. U.S. Building Codes specify minimum specifications for acceptable egress windows for first and second floors. See Egress.pdf for requirements.
Extrusion. Produced by forcing heated material (vinyl, aluminum, steel) through an orifice in a die to create lengths of shaped material, extrusions of various types make up the materials that are precisely cut to create our window frames. The term Lineal is also common when referencing vinyl extrusions.
Eyebrow windows. Related to an arch window, an eyebrow shaped window is effectively an arch window with vertical side legs.
Fixed window (or Picture Window). A window with no operating components.
Float glass. Glass formed by a process of floating the material on a bed of molten metal. It produces a high-optical-quality glass with parallel surfaces, without polishing and grinding.
Foam Sealant. Sometimes used to fill a gap between the window frame and the building wall, especially if the window is too small for the opening. A properly sized and manufactured window will not require that a foam sealant is used. If foam sealant must be used, use only non-expanding types and use it sparingly!
Fogging. A deposit of moisture on the inside surface of a sealed insulating glass unit due to extremes of temperatures or a failed seal. Fogging can occur when external temperatures change rapidly or where the inside and outside temperatures differ substantially, but such fogging is temporary. If fogging is consistent regardless of the temperatures, the dual pane seal has probably failed and the IG must be replaced.
Gas fill. A gas other than air, usually argon or krypton, placed between window to reduce the U-factor, the winter efficiency measurement of a window. (See Argon)
Glazing. The glass or plastic panes in a window, door, or skylight.
Glazing bead. A molding or stop around the inside of a window frame to hold the glass in place.
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.
Heat-strengthened glass. Glass that is heated to just below melting point and then rapidly cooled. Heat-strengthening glass increases its strength beyond that of typical annealed glass. The most common heat-strengthened glass is tempered (or Safety) glass.
Hopper. Window similar to a casement except the sash is hinged at the bottom and always swings out along the top edge. See awning and casement windows.
Horizontal slider. A window with a movable panel that slides horizontally.
IECC. International Energy Conservation Code published by the ICC. The successor to the Model Energy Code, which is cited in the 1992 U.S. Energy Policy Act (EPAct) as the baseline for residential Energy Codes in the United States.
Infiltration. See air leakage.
Infrared Radiation. Invisible, electromagnetic radiation beyond red light on the spectrum, with wavelengths greater than 0.7 microns. More importantly, infrared light is felt as heat and is the key component in controlling energy costs during summer. (See Low-E)
Insulated Glass or IG. See Double Pane Glass.
Krypton. See Argon or Gas Fills. Krypton is substantially higher in cost than Argon but is the more effective insulating gas for extreme winter conditions. Used in an EnergyCore™ triple pane, krypton can improve the insulating capability to R-7.
Laminated glass. Two or more sheets of glass with an inner layer of transparent vinyl or resin, heat bonded together. Used for both safety (the glass adheres to the inner layer if broken), infiltration control (even with broken glass the inner layer is difficult to break, keeping debris and rain out) and for noise control. (See Noise Reduction
Lite. See Divided Lite
Light-to-solar-gain ratio (or LSG). While we all want to reduce the energy costs caused by Houston’s intense summer sun, most of us still want to allow in as much natural light as possible. LSG is a derived measurement from two other NFRC window ratings and is based upon dividing the Visible Light Transmission by the Solar Heat Gain Coefficient. A higher LSG results in a window that allows more visible light while also blocking infrared heat. A low LSG that blocks a similar amount of solar infrared is darker and allows less natural light.
Low-emittance (Low-E) coating. Microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface that suppresses or reflects radiative heat flow. Low-E coatings are ‘spectrally selective’, i.e. they are transparent to visible light and reflective of infrared (heat) radiation as well as substantially reducing harmful UV radiation.
Metal-clad windows. Wood windows whose exterior surfaces are covered with extruded aluminum or other metal, with a factory-applied finish to deter the elements.
Mullion. A major structural vertical or horizontal member between window units or sliding glass doors.
Muntin. A secondary framing member (horizontal, vertical, or diagonal) to hold the window panes and divided lites in place in a single pane window. In a modern insulated window wood, plastic, or metal muntins (often referred to as grids) are placed between the panes of insulated glass to create the appearance of divided lites.
Nailing fin. An extension of a window frame which generally laps over the conventional stud construction and through which screws or nails are used to secure the frame in place. Used for new construction windows but not generally used for remodeling and replacement.
NFRC. National Fenestration Rating Council. The NFRC provides the measurement parameters for key window ratings such as U-Factor, SHGC, etc. and also sets the requirements for window labels to convey these ratings to consumers.
Noise Reduction. Sound vibrations are transmitted through every building material, but single pane windows especially transmit a significant amount of noise into a home. Simply adding a storm window can decrease noise levels in a cost efficient manner while replacing single pane windows with modern insulated windows combines superior energy efficiency with noise reduction. And for difficult problems, Custom Windows can improve things further by using special STC glass or laminated glass solutions that provide even greater noise reduction.
Obscure glass. Any textured glass (frosted, etched, fluted, ground, etc.) used for privacy, light diffusion, or decorative effects.
Operable window. Window that can be opened for ventilation. (See Single and Double Hung)
Panel. A major component of a sliding glass door, consisting of a light of glass in a frame installed within the main (or outer) frame of the door. A panel may be sliding or fixed.
Picture window. A large, fixed window framed to provide a panoramic view.
Plate glass. A rolled, ground, and polished product with true flat parallel plane surfaces. It has been replaced by float glass.
Polyvinylchloride (PVC). An extruded or molded plastic material used for window framing and as a thermal barrier for aluminum windows.
R-value. A measure of the resistance of a glazing material or fenestration assembly to heat flow. It is the inverse of the U-factor (R = 1/U). Single pane windows commonly are R-1, while modern Low-E windows are R-3 or better. Custom Windows currently manufactures windows up to R-6.
Radiation. The transfer of energy in the form of electromagnetic waves from one separate surface to another. Energy from the sun reaches the earth by radiation in the form of heat (infrared), fading (UV) and visible light.
Reflective glass. Window glass coated to reflect radiation striking the surface of the glass.
Refraction. The deflection of a light ray from a straight path when it passes at an oblique angle from one medium (such as air) to another (such as glass).
Rough opening (RO). The opening in a wall into which a door or window is to be installed. Used primarily for new construction windows with nailing fins. Actual window frames are generally ½ inch smaller than the RO.
Safety glass. A strengthened or reinforced glass that is less subject to breakage or splintering. While tempered glass is the most common, laminated glass is also classed as a safety glass.
Shading coefficient (SC). A measure of the ability of a window or skylight to transmit solar heat, relative to 1/8-inch clear, double- strength glass. SC has been phased out in favor of Solar Heat Gain Coefficient (SHGC).
Simulated divided lights (SDL). A window that has the appearance of a number of smaller panes of glass, but is actually a larger glazing unit with the muntins placed on the exterior surface of the glass. Windows using SDLs provide a more traditional appearance.
Single glazing. Single thickness of glass in a window or door. For most residential purposes, single glaze windows can only be used to replace a broken single glaze window since energy codes now require insulated glass units in place of single glazing.
Single-strength glass. Also called SSB, single-strength glass is approximately 2.5mm thick. Modern windows can be produced using single strength glass and are often used in new construction for cost savings. Custom Windows, however, will only produce using heavier double strength glass at minimum.
Solar heat gain coefficient (SHGC). The fraction of solar radiation admitted through a window or skylight. Unlike Shading Coefficient, SHGC includes both directly transmitted energy as well as absorbed and reradiated energy. It is expressed as a number between 0 and 1. The lower a window’s SHGC, the less solar heat it transmits. SHGC is the most critical measurement of a window’s energy efficiency in a climate like Houston’s than U-Factor which is a winter rating.
Solar screen. A sun shading screens that is installed to reduce solar radiation. It is not spectrally selective, however, so visible light and heat are both reduced to some degree. Custom Windows does build solar screens as well.
Sound Transmission Class (STC). The sound transmission loss rating of a material over a selected range of frequencies. The higher the number, the less sound transmitted. STC in windows can be significantly improved by adding a storm window to a single pane window or replacing single pane windows with modern dual-pane windows. Even greater STCs can be obtained by using insulated glass with different thicknesses for each pane or using laminated glass in either a monolithic or insulated unit.
Spectrally selective. A coated glazing (typically Low-E) with optical properties that are transparent to some wavelengths of energy and reflective to others. Advances in Low-E coating technologies continues to improve the spectrally selective properties in insulated glass units, allowing most of the natural light while reducing significant amounts of the solar heat and ultraviolet radiation from entering the home.
Storm windows. A second set of windows installed on the outside or inside of the primary windows to provide additional insulation, wind protection and/or noise reduction. Glazed with a polycarbonate or laminated glass, storm windows can also significantly increase security.
Tempered glass. Treated glass that is strengthened by heating the glass to just below its melting point and then rapidly cooling it. This process changes the molecular structure so that if shattered, it breaks into smaller, more rounded pieces than non-tempered glass. Tempered glass is approximately five times stronger than annealed glass and is required by code as safety glazing in patio doors, entrance doors, side lights, and other hazardous locations. See tempered.pdf for the most common situations requiring tempered glass.
Thermal break. An element of low conductance placed between elements of higher conductance to reduce the flow of heat. Used in aluminum windows such as Custom Windows’ T110 windows.
Tilt Sash. A single- or double-hung window whose operable sash can be tilted into the room.
Tilt-Turn Window. Common in Europe, a tilt-turn window can either be opened in two different directions. With one motion of the handle, the entire sash can swing inward like a door or, by moving the handle again, can be tilted in at the top to allow ventilation without compromising security. Custom Windows builds Tilt-Turn Windows.
Tinted glass. Glass colored by incorporation of a mineral admixture. While tinting can reduce some heat gain, tinting is not spectrally selective so it reduces visible light as well.
Transom. A horizontal window above a door or other window.
U-factor (U-value). A measure of the rate of non-solar heat loss or gain through a material or assembly. Importantly, for windows this is measured using extreme winter conditions of 0° F outdoor temperature, 70° F indoor temperature, 15 mph wind, and no sun and would vary if the measurements were conducted at more common Houston winter temperatures. U-factor ratings are improved with the use of an inert gas such as Argon and may be required to achieve the specifications required for a tax credit.
Ultraviolet light (UV). Invisible solar radiation that is outside of the visible spectrum at short-wavelengths beyond visible violet light. Ultraviolet rays are a component of sunlight and can cause fading of paint, carpets, and fabrics as well as some skin cancers. Spectrally selective glass such as Low-E coated glass significantly reduces UV radiation into the home by up to 95%.
Vinyl. Polyvinyl chloride material, which can be both rigid or flexible, used for window frames.
Vinyl-clad window. A window with the exterior wood covered with extruded vinyl.
Visible light. The portion of the electromagnetic spectrum that produces light that humans can see. Wavelengths range from 380 to 720 nanometers.
Visible transmittance (VT). The percentage or fraction of the visible spectrum (380 to 720 nanometers), weighted by the sensitivity of the eye, that is transmitted through the glazing. VT ratings of windows will be less than the VT rating of the glass alone due to the influence of the type of window, frame and window elements such as divided lites.
Warm-edge technology. The use of low-conductance spacers to reduce heat transfer near the edge of insulated glazing. Every Custom Windows IG incorporates spacers with warm-edge technologies.
Weep hole. A small opening in a wall or window sill member which allows water or condensation to drain outside.- See more at: https://www.custom-windows.net/resources/glossary/#shg