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Air infiltration

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

Air leakage

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

Annealed glass

Standard sheet of float glass which is heat-treated to increase its impact resistance


Heating above the critical or recrystallization temperature, then controlled cooling of metal, glass, or other materials to eliminate the effects of cold-working, relieve internal stresses, or improve strength, ductility, or other properties


An inert, non-toxic gas often used in insulating glass units to reduce heat transfer



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

Bay window

An arrangement of three or more individual window units, attached so as to project from the building. A bay window can be distinguished from a bow window by the fact that you can stand inside the projection created by a bay window


A fixing strip which holds the glass into the frame. Security beads will be fitted on the inside of the window so as to prevent the removal of the bead by potential burglars on the outside of the property

Bow window

An arrangement of three or more individual window units, attached so as to project from the building. A bay window can be distinguished from a bow window by the fact that you can stand inside the projection created by a bay window



A window sash that swings outwards to open

Composite frame

A frame consisting of two or more materials for example, a GRP material, which is comprised of Glass Reinforced Plastic


The deposit of water vapour from the air on any cold surface which has a temperature that is below the dew point - such as a cold window glass or frame that is exposed to humid indoor air


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


A heat transfer process involving motion in a fluid (such as air) caused by the difference in density of the fluid and the action of gravity. Convection affects heat transfer from the glass surface to room air, and between two panes of glass



A crystalline substance used to absorb moisture and prevent excess humidity. Everest use desiccant substances to absorb the moisture from within the sealed air space on our insulating glass units


The temperature at which water vapour in air will condense at a given state of humidity and pressure

Double Door

Also known as a French door, double doors are made from two connected door panels which can be designed to swing inwards or outwards. They are particularly popular back door designs which can grant easier access to your garden

Double glazing

In general, two panes of glass separated by an air space within an opening 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 and the space is sealed airtight, eliminating possible condensation and providing superior insulating properties


A projecting fin or a groove at the outer edge of a sill, soffit, or other projecting member in a wall designed to interrupt the flow of water downward over the wall or inward across the soffit


Edge Effect

The heat transfer that occurs at the edge of a glazing unit due to the thermal properties of sealants and spacers


A window hinge that allows the window to be opened to 90 degrees to enable escape in the event of an emergency

Emergency Exit

A window large enough for a person to easily climb out of in case of fire or other emergency

Energy rating

A system that calculates the energy efficiency of windows and other forms of glazing. Everest uPVC Casement Windows carry an A-rating from the British Fenestration Rating Council (BFRC), which is the highest achievable grade


The process of producing vinyl or aluminium shapes by forcing heated material through an orifice in a die. Also, any item made by this process



A half-circle window over a door or window, often with radiating bars


The placement of window openings in a building wall, one of the important elements in controlling the exterior appearance of a building. Also, a window, door, or skylight and its associated interior or exterior elements, such as shades or blinds


A composite material made by embedding glass fibres in a polymer matrix. May be used as a diffusing material in sheet form, or as a standard sash and frame element


A coating applied to the outer surface of a material to improve its performance and/or aesthetics

Fixed light

A pane of glass installed directly into non-operating framing members

Fixed panel

An inoperable panel of a sliding glass door or slider window

Fixed window

A window with no operating sashes

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

Floating Mullion

A dummy central post that sits vertically in a window frame between two opening sashes, but which is actually attached to one of the sashes so as to provide an unobstructed space when the window is open (usually for escape in the event of an emergency)


A deposit of contamination left on the inside surface of a sealed insulating glass unit due to extremes of temperatures or failed seals


The fixed frame of a window which holds the sash or casement as well as hardware


Gas fill

A gas, other than air, placed between window glazing panes to reduce the U-factor by suppressing conduction and convection

Georgian Bar

Traditionally a Georgian style window was made up of several small panes of glass fixed within a matrix of horizontal and vertical bars. In modern windows this effect is achieved by applying narrow strips of profile to the outer surface of the glass which will be aligned with a spacer bar between the panes of the sealed unit so that it appears as though the window is made up of multiple smaller glazed units – this is know as ‘authentic’ Georgian bar (see also Georgian effect)

Georgian Effect

Unlike authentic Georgian bar designs (see above), a window with a Georgian effect does not have profile on the outer surface of the glass. This makes the surface of the glass easier to clean as it is unobstructed


An inorganic transparent material composed of silica (sand), soda (sodium carbonate), and lime (calcium carbonate) with small quantities of alumina, boric, or magnesia oxides


The glass or plastic panes in a window or door

Glazing bead

A moulding or stop around the inside or outside of a window frame to hold the glass in place. Security beads will be fitted on the inside of the window so as to prevent the removal of the bead by potential burglars on the outside of the property


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

Horizontal slider

A window with a movable panel that slides horizontally



Construction materials used for protection from noise, heat, cold or fire


An upright frame member of a panel in a sliding glass door which engages with a corresponding member in an adjacent panel when the door is closed. Also called interlocking stile



A vertical member at the side of a window frame, or the horizontal member at the top of the window frame, as in head jamb



A third party accreditation confirming that the product meets the requirements of the British or European standard. Everest products carry numerous Kitemarks from the British and European Standards authorities and are regularly tested to ensure they maintain their high standard of quality


An inert, non-toxic gas used in insulating windows to reduce heat transfer

KWH (KiloWatt Hour)

Unit of energy or work equal to one thousand watt-hours


Laminated glass

Two or more sheets of glass with an inner layer of transparent plastic to which the glass adheres if broken. Used for safety glazing and sound reduction

Lift Handle

Handle used for raising the lower sash in a vertical sliding sash window. Also called sash lift


A window; a pane of glass within a window. Double-hung windows are designated by the number of lights in upper and lower sash, as in six-over-six. Also spelled informally lite


A horizontal member above a window or door opening that supports the structure above

Low-emittance (Low-E) coating

Microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window glazing surface primarily to reduce the U-factor by suppressing radiative heat flow. A typical type of low-E coating is transparent to the solar spectrum (visible light and short-wave infrared radiation) and reflective of long-wave infrared radiation



The time and effort it takes to keep your home improvements in full-working order and looking their best. Everest products are designed to be as low-maintenance as possible, through our use of high-quality materials and craftsmanship, and our comprehensive long-term guarantees


A major structural vertical or horizontal member between window units or sliding glass doors (see also floating mullion)


A secondary framing member (horizontal, vertical, or diagonal) to hold the window panes in the sash. This term is often confused with mullion



Obscure glass

Glass that incorporates a textured design, such as frosting, etching, fluted glass etc. Obscure glass is typically used in double glazed windows, patio doors or conservatories to protect the privacy of the homeowner, or for decorative effect

Operable window

Window that can be opened for ventilation


A style of conservatory based on the popular designs of renaissance-era Italy where the structure contains less glass than in a conventional conservatory. Everest orangeries combine authentic period features with modern design benefits



One of the compartments of a door or window consisting of a single sheet of glass in a frame; also, a sheet of glass


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

Patio doors

A style of door that features sliding glass panels for ease of access and maximum glazed areas. This design is most popular as a back entrance, opening out onto your garden or balcony



Modern weather seal made of a foam core and a polyethylene film with memory like properties



Horizontal member of a window sash


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)


Safety glass

Glass that, when broken, shatters into tiny harmless cubes (see also tempered glass)


The portion of a window that includes the glass and the framing sections directly attached to the glass, not to be confused with the complete frame into which the sash sections are fitted


A compressible plastic material used to seal any opening or junction of two parts, such as between the glass and a metal sash, commonly made of silicone, butyl tape, or polysulfide

Secondary Window

Tailor-made to fit behind your existing windows, secondary glazing allows additional warmth and security without compromising the look of your home. As a result they are most popular in traditional properties and listed buildings

Sheet glass

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


The lowest horizontal member in a door, window, or sash frame

Single glazing

Single thickness of glass in a window or door

Spacer bar

The linear object that separates and maintains the space between the glass surfaces of insulating glass


Tempered glass

Treated glass that is strengthened by reheating it to just below the melting point and then suddenly cooling it. When shattered, it breaks into small pieces. Approximately five times stronger than standard annealed glass; is required as safety glazing in patio doors, entrance doors, side lights, and other hazardous locations. It cannot be re-cut after tempering

Thermal break

An element of low conductance placed between elements of higher conductance to reduce the flow of heat. Often used in aluminium windows

Thermal expansion

Change in dimension of a material as a result of temperature change


The member that lies at the bottom of a sliding glass door or swinging door; the sill of a doorway

Tilt Turn window

A type of window that that a dual hinge mechanism which allows the sash to be tilted inwards at the top for ventilation or opened fully inwards, on side hinges, for cleaning of the outside surface of the window

Tinted glass

Glass coloured by the incorporation of a mineral admixture. Any tinting reduces both visual and radiant transmittance


The percentage of radiation that can pass through glazing. Transmittance can be defined for different types of light or energy, e.g., visible light transmittance, UV transmittance, or total solar energy transmittance


A horizontal transverse beam or bar in a frame; a crosspiece separating a door or the like from a window or fanlight above it. Also, a window above a door or other window, built on and commonly hinged to a transom

Transom window

The window sash located above a door. Also called transom light


U-factor (U-value)

A measure of the rate of non-solar heat loss or gain through a material or assembly. It is expressed in units of Btu/hr-sq ft-°F (US) or W/sq m-°K (European metric). Values are normally given for NFRC/ASHRAE winter conditions of 0° F (18° C) outdoor temperature, 70° F (21° C) indoor temperature, 15 mph wind, and no solar load. The U-factor may be expressed for the glass alone or the entire window, which includes the effect of the frame and the spacer materials. The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating value. To convert the U-factor from US (imperial/IP) to European (metric/SI), multiply the imperial number by 5.678. For example, If U=0.35 Btu/hr-sq ft-°F in imperial units, then 0.35*5.678 = 1.9873. The U-factor in metric units will be 1.9873 W/sq m-°K

Ultraviolet light (UV)

The invisible rays of the spectrum that are outside of the visible spectrum at its short-wavelength violet end. Ultraviolet rays are found in everyday sunlight and can cause fading of paint finishes, carpets, and fabrics



The movable framework or sash in a glazed window that is hinged or pivoted to swing open; also describes a mechanism which allows air to circulate from inside a room to outside, and vice versa


Warm-edge technology

The use of a low-conductance spacer bar to reduce heat transfer near the edge of insulated glazing

Weather stripping

A strip of resilient material used for covering the joint between the window sash and frame in order to reduce air leaks and prevent water from entering the structure


A glazed opening in an external wall of a building; an entire unit consisting of a frame sash and glazing, and any operable elements

Window hardware

Various devices and mechanisms for the window including catches, fasteners and locks, hinges, pivots, lifts and pulls, pulleys and sash weights, sash balances, and stays