Keeper:
The hook-shaped piece of hardware that it is mounted on the inside sash stile of a casement window in which the sash lock engages.
Knocked-down:
Not assembled. Parts for a window frame pre-manu¬factured for assembly later on a job site.
Label:
A projecting molding by the sides and over the top of an opening.
Label stop:
Ornamental projection on each end of a label, sill, or sill course. Often takes the shape of a gargoyle or other decorative carving.
Labeled window:
Windows bearing fire-rating labels of Underwriters’ Laboratories (UL).
Laminated glass:
Similar to the construction of car windshields, this technique sandwiches a piece of transparent film or plastic between two panes of glass. Typically used for safety reasons because of its resistance to shattering. Also reduce noise transmission to the interior.
Lancet window:
Tall, narrow window with a pointed-arch top, often with leaded diamond shaped lights; characteristic of Gothic architecture.
Lattice window (also lozenge):
Window with glazing bars set diagonally.
Lead light (also lead glazing; stained glass): Window with small panes of glass set in grooved rods of cast lead or came. The glass may be clear, colored, or stained.
Lift:
A handle or grip installed on the bottom sash rail of a double-hung window to assist in the raising or lowering of the sash.
Light (also lite):
A window; a pane of glass within a window. Double-hung windows are designated by the number of lights in the upper and lower sash, as in 6-over-6.
Lintel:
Horizontal member (wood, steel, or stone) over a window opening to support the weight of the wall above. A header.
Loop window (also Balistraria):
A long and narrow vertical opening, usually widening inward, cut in a medieval wall, parapet, or fortification for use by archers. Modifications appear in Roman¬esque Revival architecture.
Low-E Glass:
A term used to refer to glass which has low-emissiv¬ity due to a film or metallic coating on the surface of the glass. Usually constructed of dual, sealed panes of coated glass filled with pure inert gas to block ultraviolet heat, for cooling purposes, while reflecting room heat back into the room for heating purposes.
LVL:
Laminated Veneer Lumber – A combination of many pieces of veneered lumber glued together to give added structural capabilities. Often used in window or door frames.
Masonry Opening:
The space in a masonry wall left open for the window or door.
Meeting rail (also lock rail):
One of the two horizontal members of a double-hung sash which come together. A check rail.
Meeting stile:
The vertical member in a pair of stiles, as in abutting casement windows.
Mold stone (also jamb stone):
A stone that serves as a window jamb.
Mortise:
A slot or rectangular cavity cut into a piece of wood to receive another part.
Mortise and tenon:
A strong wood joint made by fitting together a mortise in one board and a matching projecting member (tenon) in the other.
Mullion:
A vertical member (usually wood or metal) to structurally join two window or door units.
Muntin:
Vertical or horizontal bars used to separate glass in a sash into multiple lights. Often called a grille.
Nailing Fin:
A vinyl or aluminum extension attached to the frame of a window or door which creates a positive seal be¬tween the window and the framed wall. Acts as an additional barrier against air and water leakage. Screws or nails are fastened through the fin to hold the unit in the opening.
NFRC label:
NFRC stands for the National Fenestration Rat¬ings Council. This non-profit trade group sets energy standards for windows - the NFRC label shows everything you need to know about the window you’re
considering.
North-light roof:
Sawtooth roof with north-facing clerestory windows.
Ogee curve (also ogee molding):
Reverse flex curve commonly found in window moldings and trim pieces.
Operable window:
Window which can be opened for ventilation.
Operator:
A metal arm and gear attached to a window which al¬lows for easy operation.