Annealed Glass:  Glass as we commonly know it.  Water glasses, most window panes and glass jars are made from annealed glass.  Annealed glass is manufactured in a variety of thicknesses, colors, and patterns.

Casement Window:  A projecting window with a single sash hinged at the sides and usually opening outward like a door and operated by a crank handle that turns to open or close the unit.

Dessicant:  A drying agent (such as silica gel) used by some manufacturers between the panes of insulating glass (in the edge spacer) to prevent “fogging” between the panes.

Double Hung Window:  Two sashes which move vertically, by-passing each other in a single frame.  Sash may be counter-balanced by weights or springs.

Fenestration:  The placement of window openings in a building wall; one of the important elements in controlling the exterior appearance of a building, its ventilation, light, etc.

Fixed Window:  Window that is non-operative (does not open).

Horizontal Slider:  Single vent which moves horizontally, with one fixed side.

Insulating Glass:  Double or triple glazing with an enclosed, dehydrated, and hermetically sealed airspace between the panes.

Insulated Window:  A window with multiple glazing that provides one or more air spaces between layers of glazing.

Laminated Glass:  A glass made with plates of plastic or resin or other material between two sheets of glass to prevent shattering.

Low-E Glass:  Stands for Low-Emissivity.  Glass that has been given a special micro-thin coating (usually silver and metal oxides) that blocks the passage of radiant heat through the glass for energy efficiency without appreciably affecting the view through the glass.

Neoceram Glass:  Super heat resistant glass ceramic for industrial use.  Also used in wood stoves and fireplaces. 

Obscure Glass:  A glass (frosted, etched, fluted, ground, etc.) for privacy, light diffusion or decorative purposes.

Picture Window:  Large fixed windows.

R-Value (Thermal Resistance):  Is the measure of thermal resistance of a glazing system expressed in sq ft/hr/degrees Fahrenheit/BTU.  The higher the R-Value, the less heat  transmitted through the glazing material.

Rough Opening:  The opening left in a frame wall to receive a window or door.

Safety Glass:  A strengthened or reinforced glass that is less subject to breakage or splintering, such as glass in doors and some windows.  Laminated and tempered are the most common.

Shading Coefficient (SC):  The ratio of the solar heat gain through a specific fenestration to that of a lite of 1/8” clear glass.  Since the shading coefficient of 1/8” clear glass is benchmarked at 1.00, the SC of any other fenestration will be less than 1.00, except for that of a thinner lite of clear glass, which can be greater than 1.00.

Solar Heat Gain Coefficient (SHGC):  The amount of solar radiation that enters a building as heat.  The lower the number, the better the glazing is at preventing solar heat gain.

Tempered Glass:  Special heat-treated, high-strength safety glass that shatters into pebble-sized particles but not into slivers when broken.  Required by federal, state and local laws in doors, sidelights, and some windows.

Total Solar Transmission (Tsol):  In the total solar spectrum (300 to 2,500 nanometers), the percentage of light that is transmitted through the fenestration.

Total Solar Reflectance (Rsol):  In the solar spectrum, the percentage of solar energy that is reflected from the glass surface(s).  Rsol #1 equals the percentage of reflectance from the front (outward) surface.  Rsol #2 equals the percentage of reflectance from the back (inward) surface.

U-Value:  This represents the heat flow rate through a window expressed in BTU/hr/ft2/°F, using winter weather conditions of 0°F outside and 70°F inside.  The smaller the number, the better the window system is at reducing heat loss.

Visible Light Transmission (Tvis):  The portion of energy in a spectral region from 300 to 700 nanometers.  This region includes all of the ultraviolet energy and most of the visible spectrum, and will give the best representation of relative fading rates.  The lower the number, the better the glass is for reducing fading potential of carpets and interior furnishings.

Visible Reflectance (Rvis):  In the visible spectrum (380 to 720 nanometers), the percentage of visible leght reflected from the glass surface(s).  Rvis #1 equals the percentage of visible reflectance from the front (outward) surface.  Rvis #2 equals the percentage of visible reflectance from the back (inward) surface.

Weep Hole:  Small holes drilled along the bottom edge of a storm sash, combination storm-screens or windows with pocket sills to permit moisture condensation or wind-driven rain to drain away from the sill to the outdoors.