The Fenestration Glossary

TERM	MEANING
sash	The inner frame which holds glass in operable and fixed window units.
sash	the operating portion of a hung or horizontal sliding window. A single assembly of stiles and rails made into a frame for holding glass. The framework holding the glass in a window unit. It’s composed of two stiles (sides) and two rails (top and bottom).
sash balance	A coiled spring or spiral system integrated into the jamb liners to allow double hung or single hung sashes to open and close. They also allow the sashes to remain open in varied positions..
sash cord	In double-hung windows, the rope or chain which attaches the sash to the counter balance.
sash lift	A protruding handle screwed to the inside bottom rail of the lower sash on a double-hung window. Available on all Pella double-hung windows.
sash lock	Generally, a cam-action lock applied to the check rails of a double/single hung window, or sliding window to pull the check rails tightly together. They are also applied to the open edges of a projecting window to seal the sash tightly to the frame. Sash locks provide security and weatherability.
sash stop	cover in jamb track that reduces sash travel on hung windows.
sash weights	In older double-hung windows, the concealed cast-iron weights which are used to counterbalance the sash.
screw boss	a continuous screw track in an extrusion. The track is designed to accept a specific diameter sheet metal screw to provide a secure means of fastening extrusions without the use of reinforcement.
sealed unit	See Insulating Glass Unit.
SEAT BOARD	A flat board cut to fit the contour of a bow or bay window that’s installed between the sills and the flat wall surface. They provide a seat or shelf space.
SGCC	Safety Glazing Certification Council - administers tempered glass testing and certification program.
shading coefficient	The measure of how well glazing blocks solar heat gain relative to 1/8" clear glass under the same conditions. The lower the shading coefficient, the better the unit blocks solar heat.
shims	Wood wedges used to secure the window or door unit in the rough or masonry opening in a square, level and plumb position during and after installation.
side lights	Tall, narrow, fixed or operating sash on either or both sides of a door to light an entryway or vestibule. Narrow fixed units mulled or joined to door units to give a more open appearance. Tall, narrow, fixed or operating sash on either or both sides of a door to light an entryway or vestibule.
sidelight	A narrow fixed unit joined to one or more doors, providing a more open appearance.
sill	The bottom of a door or window frame.
sill	The main horizontal member forming the bottom of the frame of a window or door. The horizontal piece that forms the bottom of a window frame. It is generally slanted down to the outside to shed standing water. The lower horizontal member of a window frame.
sill angle	extrusion that, when applied below the window, permits the gap below the window to be closed after window installation.
sill course	The row of bricks, cement blocks or stones laid horizontally at the bottom of a masonry opening.
simulated divided light	A method of constructing windows in which muntins are affixed to the inside and outside of a panel of insulating glass to simulate the look of true divided light.
single glazing	Use of single panes of glass in a window. Not as energy-efficient as double glazing.
single strength glass	(SSB) 3/32" thickness.
single-hung	A double-hung type of window in which the top sash is fixed or inoperable
skylight	A special window set into a roof to provide natural light.
slider	A type of window with one fixed sash, and one that slides sideways -- good where outside clearance is limited.
sliding window	A window with two or more sashes that slide horizontally past each other within the frame.
solar gain	The absorption of heat from the sun -- the amount of solar radiation (measured in BTUs) received by a surface. Glazing with Solar Gain Low E coatings optimize the collection of the sun's heat, and should be used when heat gain is desired.
solar heat gain coefficient	The fraction of incident solar radiation entering a home through the windows -- the lower the number, the better the window is at blocking heat gain. See Solar Shield.
solar shield	The shielding or blockage of the sun's heat. Willmar's Solar Shield Low E coatings provide solar shading, blocking heat gain from the sun. Glazing with Solar Shield coatings should be used when there is potential for excessive heat gain, or when heat gain is undesirable.
solar tempered house	A dwelling that obtains a large part of its heat from the sun.
solar transmittance	The percentage of total solar energy that glazing transmits through a window -- a standard clear dualpane has a solar transmittance of 71%.
sole plate	The bottom horizontal piece in a frame wall, usually single or double 2x4’s. The wall is nailed into the deck or rough floor through the sole plate.
solid extrusion	an extruded shape other than a hollow or a semi-hollow extruded shape. Less costly to produce compared to semi or hollow shapes.
Sound Transmission Class (STC)	A rating measure for the ability of glazing to block out sound from outside sources. The higher the STC rating the better the sound blockage (and the quieter the home).
spandrel glass	glass mounted between floors of a building. It is usually made opaque to hide building components.
specialty	A type of window with distinct shapes, such as octagons, round-tops, ellipticals, rakeheads -- virtually any shape can be custom manufactured.
sputtered coating	A coating deposited on glass or film atom-by-atom in a precise process inside a vacuum chamber.
STC	Sound Transmission Class - describes acoustical control for interior panels, and, even though inadequate, is currently the only criteria for exterior windows. The higher the number, the better the product is at resisting typical sound frequencies excluding airplane and train noises.
stile	a vertical sash member. The vertical side pieces of a window sash or door panel. The main vertical members of the framework of a sash or door panel.
stool	An interior trim piece on a window which extends the sill and acts as a narrow shelf. The interior horizontal trim piece at the bottom of the window frame. The shelf-like piece that projects into the room.
stop	A molding used to hold, position or separate window parts.
subsill	refers to extrusions positioned to collect water leakage through mullions and products and drain it to the exterior. Used where high performance water resistance is required and for windows joined with mullions. It runs continuously across the opening width and can be spliced together to cover wide openings. The ends are sealed with end dams.
sun	Our day star and the source of life and energy on earth, located 93 million miles away, with an expected life of 5 billion years. A tremendous source of "free" energy if harnessed intelligently.
tempered glass	Glass that has been heat-treated to become more than three times stronger -- also known as safety glass because it breaks into small pebbles rather than jagged shards. It is used in sliding glass doors and windows susceptible to impact or breakage.
tempered glass	Glass manufactured to withstand greater than normal forces on its surface. When it breaks, it shatters into small pieces to reduce hazard. Glass that has first been cut to size, then heated to a very high temperature and then rapidly brought back to room temperature. It will withstand severe punishment from a blunt object; however, any pointed object will break the glass instantly and the glass will crumble into many, very small pieces.
tenon	A rectangular projection cut out of a piece of wood for insertion into a mortise.
thermal break	An air space or insulating material which prevents the direct coupling of a cold surface to a heated surface.
thermal break	an element of low conductivity (polyurethane) placed between elements of higher conductivity (aluminum) to reduce the flow of heat and cold.
thermal break	The addition of a thermal insulating material between two thermally conductive materials.
thermal bridge	The direct coupling of a cold surface to a heated surface, allowing heat transfer via conduction.
thermal mass	the amount of heat storage capacity available in a given material or assembly. Thermal mass in a home (tile floors, stone fireplace, etc.) will absorb excess heat generated during the day and store it until ambient temperature drops.
thermal radiation	Electromagnetic radiation emitted by a warm body -- the sun, cousin Frank, the cat, etc.
thermal resistance	The ability of a material to impede the flow of heat. See R-value.
thermosetting	baking the organic paint finish on aluminum to endure a tight bond and long life.
tinted glass	Glass other than clear, with a color cast or tint. Typically tinted glass absorbs and blocks heat, and reduces visible light transmittance.
tinted glass	glass of special formulation to produce light reducing and/or heat absorbing glass products (bronze, gray or green).
total unit	A basis for measurement, evaluation and performance comparison of different glazing configurations, established by a formula combining R-values of the frame area, edge of glass area, and center of glass area.
translucent	A glazing such as frosted glass, which transmits electromagnetic radiation (light) but causes scattering so that a clear image cannot be seen.
transom	A window installed above another window or door.
transom	A small window that fits over the top of a door or window, primarily for additional light and aesthetic value.
transparent	Clear glazing which transmits light without diffusion, and which can be seen through clearly.
tripane	An insulating glass unit consisting of three panes of glass with two internal air spaces.
true divided light	A term which refers to windows in which multiple individual panes of glass or lights are assembled in the sash using muntins. This traditional method of window construction does not have the strength or durability of the Integral Light Technology™ used in Pella Architect Series® windows.
U value	a measurement of heat transmission. The U value of a window is measured by the number of BTU's that will pass through each square foot of area per degree of temperature difference from one side of the window to the other (the lower, the better). U value = the number 1 divided by the R value
ultraviolet radiation (uv)	Electromagnetic radiation from the sun, with wavelengths shorter than visible light -- UV-caused fading of furnishings, artwork, etc. after prolonged exposure to direct sunlight can be a problem. Classical measurement of UV transmittance (300 -- 380 nm) is generally used to indicate fading potential and to compare UV-blocking performance of various glazing types. Krochmann is a damage-weighted function developed in Europe used by some to compare product performance.
unison lock	A casement locking system which secures the window at two locking points by operation of one handle.
united inches	the sum total of one window width and one window height expressed in inches.
u-value	Rate of heat flow-value through the complete heat barrier, from room air to outside air. The lower the U-value, the better the insulating value