Architectural and Engineering Glossary


O And M Manual

Short for “operations and maintenance” manual for a building. Also see owner’s manual.

O.c., Oc, OC

Abbr. for on center.occupancy The use, or intended use, of a building.

O.g., O.G.

Abbr. for “ogee.”


Abbr. for “on approval.”


Abbr.for “overhead.”


On drawings, abbr. for “overall.”


Abbr. for outside air intake.


A tough, hard, high density wood of the temperate climates; rather coarse textured, ranging in color from light tan to pink or brown; used for both structural and decorative applications, such as framing timbers, flooring, and plywood.


A caulking material made from old hemp rope fibers that have been treated with tar oak varnish A long oil varnish for indoor use; contains pigment which gives it a light yellow tan color.


On drawings, abbr. for “obscure.”


1.A monumental, four sided stone shaft, usually monolithic and tapering to a pyramidal tip. 2.In Egyptian art, such a shaft mostly  covered with hieroglyphs; originally erected as a cult symbol to the sun god.

Oblique Butt Joint, Oblique Joint

A butt joint which does not form a 90 angle to the axis of the piece.

Oblique Section

n a mechanical drawing, a section taken through an object at an angle (other than 90) to its longest axis.

Oblique Vault

A vault that is supported by two walls which are parallel but not directly opposite each other. Also called a skew vault.

Obscure Glass, Visionproof Glass

Translucent sheet glass, usually having one face roughened. 

Obscuring Window

A window glazed with frosted or stippled glass or the like; used to provide privacy.

Observation Of The Work

A function of the architect in the construction phase, during his periodic visits to the site, to familiarize himself generally with the progress and quality of the work, 1 and to determine in general if the work is proceeding in accordance with the contract documents.


1.A structure, generally with a rotatable dome, in which astronomical observations are carried out. 2.A place, such as an upper room, which affords a wide view; a lookout.


A natural volcanic glass,usually black, with a bright luster; has relatively low water content.

Obtuse Angle Arch

A type of pointed arch, formed by arcs of circles which intersect at the apex; the centers of the circles are nearer together than the width of the arch.

Occupancy Permit

Same as certificate of occupancy.

Occupancy Rate

The total number of persons per room, housing unit, etc.

Occupancy Sensor

An electrical switching device that turns on the lights in a room when an occupant enters and turns them off when the occupant leaves.

Occupant Load

The total number of persons that may occupy a building (or portion thereof), an elevator, etc., at any one time.

Occupational Safety And Health Administration (OSHA

An organization within the US Department of Labor, whose responsibilities include safety in the workplace; publishes standards in the US Code of Federal Regulations that govern safety in buildings during construction and during occupancy. These regulations may be obtained directly from OSHA: Occupational Safety and Health Administration, US Depart- ment of Labor, 200 Constitution Avenue, NW, Washington, DC 20210.

Occupiable Room

A space for short term human occupancy as distinct from a space for human habitation.


In insurance terminology, an accident or a continuous exposure to conditions which result in injury or damage, provided the injury or damage is neither expected nor intended.

Ocher, Ochre

A naturally occurring yellow- brown hydrated iron oxide; used as a pigment in paint and a filler in linoleum.


On drawings, abbr. for “octagon.”

Octagon Barn

A barn having an eight sided plan; relatively few of such structures were built prior to 1880, stimulated by interest in octagon houses.

Octagon House

An eight sided house, usually two to four stories high, built primarily in the  last half of the 19th century, although the octagon plan was employed in some classical buildings.Often characterized by: a large porch; exterior walls usually of wood or concrete; a low pitched roof, often topped with an eight sided cupola; occasionally a raised basement.


A temple façade or portico having eight columns in the front or end row.


The interval between two frequencies having the ratio of 2:1.

Octave Band

The frequency range between two frequencies whose ratio is exactly 2:1.

Octave Band Sound Pressure Level

The sound pressure level of the sound within a specified octave band.

Octave-band Analyzer.

An electronic instrument for measuring octave band sound pressure level; consists of a microphone, amplifier, electric filters, an indicator, and appropriate controls.

Octopartite Vault

One of the vaults covering a square space, enclosed by walls, with eight oblique cells.


1.See  roundel.2.See bull’s eye, 2.3.An opening at the crown of a dome.


On drawings, abbr. for “outside diameter.”


Same as odeum.

Odeum, Odeon

A small ancient Greek or Roman theater, usually roofed, for musical performances.

Odor Test

Same as scent test.

Odorless Mineral Spirit

A thinner composed of branch chained aliphatic hydrocarbons; used in paints because of its exceptionally low odor level.

Odorless Paint

A paint such as a water base latex paint or an oil or alkyd base paint which contains an odorless mineral spirit as a thinner; produces a minimum amount of odor during application.


In a house in the ancient Roman empire, an apartment, hall, or large room.

Off Countmesh

In a wire cloth, a count which is not the same in both directions.


1.Having an axis not along the geometric center line. 2.Not at the center point.


White containing a slight amount of gray,yellow,or other light color.


On drawings, abbr. for “office.”

Office Building

A building used for professional or clerical purposes, no part of which is used for living purposes, except by the janitor’s family.