Argon An inert, colorless, odorless gas with lower heat conduction properties than air. If the air between two panes in a double insulated glass unit is replaced with argon, the window's energy efficiency is enhanced.
Astragal A vertical wood piece attached to the edge of one window sash which closes the other sash when it closes.  
Awning Window A window style with a outward swinging sash, occasionally bottom hinged but nearly always top hinged. Typically awnings are wider than they are tall. 
Backband Trim piece added to the edge of flat trim, often used in historic restorations.
Bay Window An assembly of three windows, typically a fixed center pane with a casement or double hung flanker on either side. The flankers are joined at 30 °, 45 ° or 90 ° to the center pane.
Bow Window An assembly of windows joined together to produce a gradual outward curve.
BrickMold A decorative exterior trim around window frames which facilitates installation and covers the jamb.
Casement Window A window style with a side-hinged sash, which opens like a door. Casements are typically taller than they are wide.  
Cladding Material that covers the exterior of a window frame and/or sash, designed to provide increased durability with low maintenance.   Window manufacturers typically offer cladding in a limited variety of colors and sizes.
Cottage-Style A Single or Double Hung window with a bottom sash that is taller than the top sash. In Reverse Cottage-style windows, the top is taller than the bottom sash.
Daylight Opening The visible area of glass.
Direct Set A picture window with no sash, as opposed to Sash Set. The glass is set directly into the frame and, therefore, the window is stationary. This results in a greater daylight opening.
Double Casement Window A mulled assembly consisting of a left hinged and right hinged casement. This window style differs from a French Casement Window in that each sash is inside its own frame.
Double Insulated The modern method of creating glass units, using two panes of glass separated by a single (dead) airspace which creates an efficient insulating barrier.
Double Hung Window A non-projecting window type in which the upper (outside) sash slides down and the lower (inside) sash slides up.
Egress Window A window large enough for a person to climb out in case of emergency.   Egress hinges allow casement or awning windows to open at least 90 degrees, facilitating exit.   Egress requirements are dictated by national and local building codes. 
Finishing Foxtail Hill offers several interior and exterior window priming and finishing options.   These include primed out and in&out, stained in and in&out, and (or) finish painted in and in&out.   In all cases the first step involves immersing all wood window parts in a wood preservative/sealer which also includes a decay-resisting fungicide.  
Fir Fir is the wood of choice for window construction.   Nationally known manufacturers typically use less expensive pine instead, but fir is stronger, harder, and heavier.  Fir holds fasteners better, stains and paints better, and looks better.  Foxtail Hill uses only solid CVG (clear vertical grain) fir - no veneer, laminated, or fabricated type wood products.
Fixed (aka Non-Operating) A Non-operating/non-venting sash, like a picture window.
Flanker A window joined to the side of another window.   Flankers are the windows on either end of the center fixed window in a bay unit, for example.
Flat Trim  (aka Flat Mold) Exterior Trim, such as 1x3 or 1x4, having a flat surface, as opposed to brickmold.
Frame The enclosure in which the window sash(es) are mounted.   The outside dimension of the frame is used to size the window, either assuming a rough opening or net size.
French Casement Window A left and right hinged casement similar to a Double Casement, but using an Astragal. French casements allow an unobstructed view when open.
Geometric Window A window with a specific non-rectangular geometric shape, (e.g., triangle, trapezoid, octagon, arch, ...).
Glass Stop  (see Glazing Bead).
Glazing Glass used for windows or the act of installing glass into a window.
Glazing Bead  (aka Glass Stop)  A long, thin molded piece of wood used to secure glass to the sash or frame of a window.   The joint between the glazing bead and the glass is sealed with fully weather resistant caulking.
Head Board A flat board forming the top finished surface of a Bow or Bay window.
Hinging Hinge placement on a window.
Hopper Window A window style, similar to an awning, which is hinged at the bottom and which swings inside.
Insulating Glass Glazing comprised of two or more glass panes separated by a hermetically sealed airspace.
Jamb (aka Liner) The top and side components of a window or door frame.
Jamb Extensions Finished lumber, typically 1x4, 1x6, … extending inside from a window or door frame to accommodate different wall thicknesses.
Leaded Glass A decorative glass treatment, whereby lead strips are overlaid upon glass panes in a pattern.   Complex divide patterns, such as intricate curves and angles that cannot be feasibly made with a TDL or SDL pattern can be achieved in leaded glass.
Liner  (see Jamb Extensions)
Lite  (aka Light). A single pane of glass in a window or within a subdivision (divide pattern) of a window.  
Low-E A term referring to Low-Emissivity glass, which has favorable energy efficiency characteristics.   The lower the emissivity, the lower the amount of radiated heat and the higher the reflectivity of infrared radiation.   Low-E glass has a thin, transparent metallic coating applied to one of the interior panes which filter the sun in summer, reflecting the infrared and ultraviolet rays back to the outdoors which would otherwise increase cooling costs and fade interior furnishings.   In winter, Low-E glass offers greater comfort and reduced heating costs by deflecting room-side heat back into the room.   Since the coating is between the insulating glass panes, there are no special handling or cleaning requirements.
LSR Nomenclature The specification of a casement window assembly by the location and hinging of operators and fixed units.   For example, when viewed from the exterior, a single pushout casement hinged on the left is designated as a "Pushout Casement Left".   A mulled roto casement assembly consisting of a left hinged casement, a fixed window and a right hinged casement is designated as a  "Roto Casement LSR"; that is Left-Stationary-Right. 
Mitred Corners Foxtail Hill has mitred corner joints on its window frames and sashes, which are glued and screwed for strength and maximum cosmetic appeal - a "picture frame" look.   For extremely large units (typically casements), biscuit joints are used internally for added strength.
Mulled Assembly Joining two windows together, side by side, or top to bottom.
Mullion A structural member, usually wood or metal, which joins two window units together to make a mulled assembly.
Muntin A light-weight bar used to separate a glass pane into multiple lites (see TDLs.)
Nail Fin A strip of material, usually vinyl, installed in a groove around a window or door frame, which facilitates window installation, especially on new construction.
Net Size (aka Net) The exact outer dimensions of the window frame.   (See Rough Opening).
Non-Projecting A window in which the sash does not occupy additional space when opened.   Non-projecting windows are well suited for walkways and decks where foot traffic is likely.   A Single Hung Window, Double Hung Window or Slider Window are all examples of non-projecting windows.   These window styles, however, do not ventilate quite as well as equivalent casements or awnings.
Obscure Glass Glass with one rough surface to make it translucent, but not transparent – offering privacy.   The rough surface is on the interior of the insulating unit for easy cleaning. 
Operator A moving sash in a window. For example in a Single Hung, the bottom sash is an operator, while the top sash is fixed.
Ovolo A decorative wood glazing bead curving outward from the glass.
Picture Window A window style using only fixed units (no operators). 
Push Out Style Window A traditional casement or awning window, utilizing a latching handle.   Roto Style Windows (both casements and awnings) employ a rotary crank, which is another option.
Queen Anne Style (aka Prairie Style) – A particular divide pattern like a 'tic-tac-toe' grid with smaller outside corners. 
R-Value Resistance to heat flow, a high R-factor indicates that a window has good heat-insulating properties.  The R-Factor is the inverse of the U-Factor (R=1/U).
Radius Window A geometric window that incorporates curves; usually full-circle, half-circle, quarter-circle or elliptical.
Rails The top and bottom horizontal pieces of a window sash.  
Roto Style Window Casement or Awning windows utilizing a crank which operates a window by turning in a circular motion. Roto hardware is particularly useful for difficult to reach windows. 
Rough Opening (aka R.O.) The framed wall opening into which a window is to be installed. The  net size is usually a half inch less than the rough opening to allow for insulating and squaring the window assembly.
Sash A unit which holds the glass of a window and is separate from the frame. Sashes are comprised of stiles and rails, which surround the glass.   Glazing beads hold the glass in place.
Sash Set A window with the glass set into a sash, then the sash set into a frame.   This contrasts with a Direct Set window.   A sash set window may be stationary or venting.
Seat Board A flat board forming the bottom finished surface of and providing suppport for a Bow or Bay window.
Sight Line The proper alignment of vertical or horizontal frame bars of adjacent windows.
Sill The bottom, horizontal piece of a window frame.
Sill Horn The portion of sill nosing which extends past the side jambs.
Simulated Divided Lite  (aka SDL) A method of providing the look of a TDL, while offering the energy efficiency of one lite of insulating glass. A wood gridwork is applied to the inside and outside glass surfaces, and aluminum spacer bars between the two panes simulate the look of true divided panes, while allowing airflow throughout the single insulating glass unit.
Single-Glazing A single pane of glass, with no insulating airspace.  Many older houses utilized single-glazed windows, which are far more drafty than today's double-insulated units.
Single Hung Window A non-projecting vertical sliding window in which the bottom sash opens up to vent, while the top sash is fixed.
Slider Window  A non-projecting window type with one or more fixed sashes and one or more sashes that slide horizontally for ventilation
Sliding Door A full height sliding door similar to a sliding window.   A sliding door can have one or more fixed sashes and one or more sashes that slide horizontally for ventilation and entry/exit.   The fixed and sliding sashes are designated by the XO nomenclature.
Snap-In Grids  The simplest method to achieve a divide pattern in a window.   A wooden grid is pressure fit to the inside of the window to simulate a TDL pattern.
Spacer Bar The hollow metal bars which separate the two panes of glass to form an insulated unit.
Stationary (aka Fixed) A window that does not open.
Stiles The vertical pieces of a window sash.
Stool An interior trim piece which extends the sill platform.
Tempered Glass Plate glass with increased strength.   When broken, however, it shatters in tiny fragments, reducing the possibility of injury.   Tempered glass is required in certain applications by building code.
Track A vinyl extrusion which holds a Double Hung, Single Hung or Slider Window into the frame.
Transom A window installed immediately above another window or door.
True Divided Lite  (aka TDL) A term referring to windows in which multiple individual panes (or lites) are joined together in the sash using muntins to one larger window. True Divided Lites (or TDL's) are a traditional method used to creating divided lite windows, and are often used in historical renovations.
U-Factor  (aka U-Value) Heat transference through a door or window. A low U-factor indicates less heat transference, which is desirable for energy efficiency in windows. The U-Factor is the inverse of the R-Value (U=1/R).
Vent Unit See Operator.
Weatherstripping A material which creates a weather-tight seal between a window sash and frame.
XO Nomenclature The designation of the operating ("X") and fixed ("O") sashes of a vertical or horizontal sliding assembly,  applicable to Single Hung Windows, Double Hung Windows, Slider Windows and Sliding Doors.   As usual, the windows are viewed from the exterior.

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