O
Obscure GlassA type of glass with one surface roughened in such a way as to reduce visibility but yet allow light to enter a structure. This type of glass is often used in bathroom windows. Also referred to as translucent glass or frosted glass.
OctagonA type of fixed window with eight sides whereby opposite sides are parallel but not necessarily equal in length.
OffsetA measurement for example in a bow or bay window specifying the distance from the outer edge of the floor plate to the nailing fin line of the window unit furthermost from the floor plate.
One Over One (1/1)A double hung window with no grids in either sash. (See Light Pattern)
One-Quarter Inch Radius CornersRound corners on hardware, which may be on hinges, or other hardware items, such as ball-catches. This is one of the three standard corners on a door hinge. The other two corners are 5/8" radius and square corners. For ease of use in machining, round corners are normally used.
OpenA window frame with no glass installed. Sometimes an open frame is installed in a structure and glazed later. This is done to prevent construction damage to special glass that is very expensive or difficult to replace. (See Field Glazing)
Opening MeasurementThe hole in the wall where a window or door unit will be installed. Openings are larger than unit size to allow room for insulation and shimming the unit square. Also referred to as Rough Opening.
Operable WindowA window that can be opened for ventilation.
OperatorA metal arm and gear device which allows for easy opening and closing of projecting windows; e.g. casement and awning windows.
Operating UnitA window or door that opens. Also referred to as a vent unit or operator.
OrielA window with the meeting rail located off center of the frame. Most oriels have a 60/40 configuration.
OrientationThe compass direction that a structure faces. To optimize heat-gain, the major facade of a building should face South (a variation as much as 30 degrees east or west of south will not seriously affect performance).
Outer Frame MemberThe exterior protruding portion of a window frame which has no exterior casing.
OvalA fixed lite window in the shape of an oval.
