| Term | Definition |
| O C, on center | The measurement of spacing for studs, rafters, joists, and the like in a building from the center of one member to the center of the next. |
| O C- On Center | The measurement of spacing for studs, rafters, and joists in a building from the center of one member to the center of the next. |
| O G, or ogee | A molding with a profile in the form of a letter S; having the outline of a reversed curve. |
| O-Ring | A rubber seal used around stems of some valves to prevent water from leaking by it. |
| O/C | See OC. |
| Oak | A strong, hard, heavy wood. |
| Oak Floor | A common type of flooring, usually installed in small tongue and groove strips made of oak. |
| Oak Veneer | A thin layer of oak glued to an interior wood or bonded together to form a protective or ornamental facing; types available are white oak and red oak. |
| Oakum | Loose hemp or jute fiber that's impregnated with tar or pitch and used to caulk large seams or for packing plumbing pipe joints |
| Oakum | Loosely twisted jute or hemp fiber impregnated with tar and used in caulking seams, as in wood shipbuilding or in caulking cast iron bell and spigot piping. |
| Oatmeal Paper | Wallpaper made by sprinkling sawdust over adhesive surface. |
| OB | Octave Band. |
| Obelisk | A tall, slender, tapering, usually 4-sided, stone monument surmounted by a pyramid, of Egyptian origin. |
| Oblique | 1. An angle; neither parallel or perpendicular. 2. Not symmetrical with its base. |
| Oblique Slip Fault | A combination of normal and slip or thrust and slip faults whose movement is diagonal along the dip of the fault plane. |
| Obscure Glass | Ground glass or frosted glass that transmits light but does not allow a view of objects on the other side. |
| Obsolescence | The loss of value due to being no longer useful. |
| Obtuse Angle | An angle of over 90 degrees but less than 180 degrees. |
| Obtuse Triangle | A triangle having one angle over 90 degrees. |
| OC | 1. On center; the designation of spacing for framing members in a building from the center of one member to the center of the next; also shown as O/C. 2..See Oxygen Cutting. |
| Occupancy | A building code term referring to the use of a building, such as school, office, restaurant, warehouse, or residence. |
| Occupancy Importance Factor (I) | A building code term used to identify occupancies of importance. |
| Occupational Safety & Health Administration (OSHA) | U.S. Department of Labor/OSHA, 200 Constitution Avenue, NW, Washington DC, (202) 219-7725. |
| Ochre | An earth pigment, usually red or yellow, made from impure iron ore, used in paint. |
| Octave | Frequency difference between harmonic vibrations; it is the doubling of the frequency of sound. |
| Octyl Alcohol-Ethyl Hexanol | Additive in absorption machines to reduce surface tension in the absorber. |
| Oculus | 1. A circular opening or eye in a dome. 2. Any round window. |
| OD | Outside Diameter. |
| Odor | That property of air contaminants that affect the sense of smell. |
| Off Cycle | That part of a refrigeration cycle when the system is not operating. |
| Off-Site | Anything not on the subject building site. |
| Offer | A promise that is enforceable if accepted. |
| Offeror | A person who makes an offer. |
| Office | A room or building where business activities are conducted. |
| Office Building | A building containing business offices. |
| Office Cubicle | A small compartment unit, surrounded by fixed or movable walls on two or three sides, where an individual works. |
| Office Park | A planned, usually suburban, community of office buildings with common management, parking, landscaping, and other services. |
| Office Partition | Moveableinterior wall, used to partition off an office area, assembled together to create cubicles for employees. |
| Office Safe | A locked receptacle that holds money or valuables in an office; usually rated by the manufacturer to designate fire-worthiness and strength. |
| Office Trailer | A highway vehicle parked on a job site, designed to serve wherever needed, as an office and a place to carry out business. |
| Offset | 1. A combination of elbows or bends which brings one section of pipe out of line and back in line parallel with the original sector. 2. A course of masonry units that sets in from the course that is directly below it; also called Set Back, Set In, or Set |
| Offset Cabinet Construction | A method of building cabinets where the back corners of the doors and drawer fronts are rabbeted so they overlap the face frame, thereby concealing the joint. |
| Offset Connector | A fitting that is a combination of elbows or bends which brings one section of pipe out of line with, but into a line parallel with, another section. |
| Offset Hinge | A hinge with a 90 degree offset in one or both legs, designed to shift the center of rotation of the door. |
| Offset Nipple | A fitting, threaded at both ends, that is a combination of elbows or bends which brings one section of pipe out of line with, but into a line parallel with, another section. |
| Offshore | The direction away from the shore, toward a large body of water. |
| OG | Ogee. |
| Ogee | A curved section of a moulding, partly convex and partly concave. |
| Ogee Molding | A molding with a modified S-shaped profile. |
| Ogee Roof | An architectural roof design which is Eastern influenced. |
| Ogive | A pointed arch. |
| Ohm (R) | Unit of measurement of electrical resistance; one ohm exists when one volt causes a flow of one ampere. |
| Ohm's Law | A law in electricity which states the relationship between voltage, amperes, and resistance; equation. Amperes(I) x Ohms(R) = Volts(E). |
| Ohmmeter | Instrument for measuring resistance in ohms. |
| Oil Absorption | A measure of the ability of pigments to absorb oil. |
| Oil Base Caulking | Caulking made with resins and other ingredients made of various oils, dispensed through a tube. |
| Oil Binding | Condition in which an oil layer on top of refrigerant liquid may prevent it from evaporating at its normal pressure-temperature. |
| Oil Burner Nozzle | A spraying device which atomizes fuel oil into a fine spray and increases the combustion characteristics of the fuel. |
| Oil Colors | Colors ground to form of paste in linseed oil. |
| Oil Fired Boiler | A boiler that is heated by a unit that sends oil under high pressure to a nozzle, where it is sprayed as a mist and ignited by an electric spark. |
| Oil Furnace | A furnace that burns heating oil. |
| Oil Length | Oil length in varnish is measured by the oil in gallons per hundred pounds of resin; a long-oil varnish is tougher than a short-oil varnish; rubbing varnish is a typical short-oil varnish and spar varnish is a typical long-oil varnish. |
| Oil of Vitriol | See Sulphuric Acid. |
| Oil Paint | Paint in which a drying oil is the vehicle. |
| Oil Separator | Device used to remove oil from gaseous refrigerant. |
| Oil Soluble | Capable of being dissolved in oil. |
| Oil Stain | A wood stain consisting of oil-soluble dyes and solvents such as turpentine, naphtha, or benzol,; penetrates into pores of wood; has tendency to bleed. |
| Oil Switch | A switch or protector relay installed in a flue pipe, that will shut off a burner in case the stack does not come up to a predetermined temperature within 45 seconds after the motor starts. |
| Oil Tank | The storage canister where heating oil is stored for future use by an oil boiler, or an oil burning furnace system. |
| Oil Varnish | A varnish consisting of a hard resin combined with a drying oil and a drier thinned with a volatile solvent; after application, the solvent dries first by evaporation; then the oil dries by oxidation. |
| Oil, Refrigeration | See Refrigeration Oil. |
| Oil-Canning | Describing the distortion of thin-gauge metal panels that are fastened in a manner restricting normal thermal movement. |
| Oilcloth Varnish | Special highly flexible and elastic varnish. |
| Oilstone | A whetstone used with oil. |
| Oiticica Oil | Drying oil obtained from nut of oiticica tree. |
| Old English Bond | See English Bond. |
| Old Growth | Timber in or from a mature, naturally established forest. When the trees have grown during most if not all of their individual lives in active competition with their companions for sunlight and moisture, this timber is usually straight and relatively free |
| Olefin | Long-chained synthetic polymer composed of at least 85% by weight of ethylene, propylene or other olefin units; currently, only polypropylene has been produced in fiber form for carpet manufacture. |
| Olefin Plastics | Plastics based on resins made by the polymerization of olefins or copolymerization of olefins with other unsaturated compounds, the olefins being in greatest amount by weight; polyethylene, polypropylene and polybutylene are the most common olefin plastic |
| Oleoresin | A solution of resin in an essential oil that occurs in or exudes from many plants, especially softwoods; the oleoresin from pine is a solution of pine resin (rosin) in turpentine. |
| Oleoresinous Varnish | Varnish composed of resin or gum dissolved in a drying oil which hardens as it combines with oxygen from the air. |
| Olive Knuckle Hinge | A paumelle hinge with knuckles forming an oval shape. |
| On Center(O/C) | Center to center. |
| On the Stump | See Standing Timber. |
| On-Site | Objects and activities that are on the building site. |
| One Piece Toilet | A toilet where the water tank and bowl are cast in one piece of vitreous china for the purposes of quieter operation and better appearance. |
| One-Family Dwelling | A dwelling containing only one dwelling unit. |
| One-Way | Constructed with reinforcing steel running in one direction only. |
| One-Way Action | The structural action of a slab that spans between two parallel beams or bearing walls. |
| One-Way Concrete Joist System | A reinforced concrete framing system in which closely spaced concrete joists span between parallel beams or bearing walls. |
| One-Way Glass | See Transparent Mirror. |
| One-Way Solid Slab | A reinforced concrete floor or roof slab that spans between parallel beams or bearing walls, with structural reinforcing in the spanning direction only. |
| Onshore | The landward direction, away from the water. |
| Opacity | Hiding power, as of paint. |
| Opaque | Impervious to light; not transparent. |
| Opaque | Term used to describe any product that lets NO light filter through it, like the Graber Cocoon, and the Hunter Douglas Eclipse shades |
| Opaque Glaze | A non-transparent glaze with or without color. |
| Open Circuit | Electric circuit with a physical interruption caused by a switch, a break in a conductor, or an open breaker or fuse. |
| Open Compressor | An external drive compressor; not hermetic. |
| Open Decking | A deck in which the joists on the underside are exposed. |
| Open Display Case | Commercial refrigerator designed to maintain its contents at refrigerating temperatures even though the contents are in an open case. |
| Open Front Seat | A toilet seat with an open gap at the front, usually used in public toilet rooms for improved sanitation. |
| Open Graded Asphalt (Open Graded Friction Coarse) | Asphalt with a high percentage of air voids. Used in the wearing course to reduce surface water and traffic noise and to provide a higher skid resistance. Normally one size. |
| Open hole inspection | When an engineer (or municipal inspector) inspects the open excavation and examines the earth to determine the type of foundation (caisson, footer, wall on ground, etc.) that should be installed in the hole. |
| Open Listing | A listing agreement with one or more real estate brokers to sell or lease one's property on a non-exclusive basis. |
| Open Run-Around | A method of heat recovery from exhaust air in which a fluid is inserted alternately in the supply and exhaust air stream; this system transfers both sensible and latent heat. |
| Open Time | The period of time during which the bond coat retains its ability to adhere to the tile and bond the tile to the substrate. |
| Open Type Compressor | See Compressor, Open Type. |
| Open Type Decking | A deck in which the joists on the underside are exposed. |
| Open-Graded Aggregate | One containing little or no mineral filler and in which the void spaces in the compacted aggregate are relatively large. |
| Open-Graded Asphalt Friction Course | A pavement surface course that consists of a high-void, asphalt plant mix that permits rapid drainage of rainwater through the course and out the shoulder. The mixture is characterized by a large percentage of one-sized coarse aggregate. This course preve |
| Open-Grained Wood | Woods with large pores, such as oak, ash, chestnut, and walnut; also known as Coarse-Grained or Coarse Textured. |
| Open-Web Steel Joist | A prefabricated, welded steel truss used at closely spaced intervals to support floor or roof decking. |
| Operable Door | A door, of a pair, that is normally operable. |
| Operable Part | A part of a piece of equipment or appliance used to insert or withdraw objects, or to activate, deactivate or adjust the equipment or appliance, such as a coin slot, pushbutton, or handle. |
| Operating Instructions | The written explanations and descriptions furnished by manufacturers and fabricators of building equipment and components for the proper operation of their products. |
| Operating Leverage | The ratio of the percentage change in profit to the percentage change in sales. |
| Operating Pressure | Actual pressure at which a refrigerating system works under normal conditions; this pressure may be positive or negative (vacuum). |
| Operating Profit | Revenue of the business less the total of all costs of the operation. |
| Operating Room | A room in a hospital for surgical operations. |
| Operation Expenses | Total of all expenses including cost of sales, general and administrative expenses as well as indirect operating expenses. |
| Opposed Blades | Two sets of blades in a damper, linked so that the adjacent blades can open and turn in opposite directions. |
| Option | 1.Something that may be chosen. 2. A right given for a consideration to keep an offer to purchase or lease open for a specific time. |
| Optionee | 1. One who receives an option. 2. The prospective purchaser or lessee in a real estate option. |
| Optionor | 2. One who gives an option. 2. The owner-seller or lessor in a real estate option |
| Or Equal | The phrase used in specifications providing that substitutions must be equal in all relevant respects and usually subject to the approval of the architect. |
| Oral Agreement | A contract in words that are not reduced to writing. |
| Orange Mineral | Red lead prepared by roasting basic carbonate white lead; used mainly in printing ink for its characteristic color. |
| Orange Peel | 1. A pitted texture of a fired glaze resembling the surface of rough orange peel. 2. Spray painting defect in which the lacquer coat does not level down to a smooth surface but remains rough, like the peeling of an orange. |
| Orbital Sander | A hand-held platform sander that moves rapidly in a circulatory movement. |
| Ordinance | A law enacted by a city or a county. |
| Ore | Rock or earth containing workable quantities of a mineral or minerals of commercial value. |
| Organic | 1. Any chemical compound containing carbon. 2. Being or composed of hydrocarbons or their derivatives or matter of plant or animal origin. 3. Pertaining to or derived from living organisms. |
| Organic Adhesive | A prepared organic material, ready to use with no further addition of liquid or powder, used for bonding tile to back-up material by the thinset method; cures or sets by evaporation. |
| Organosol | Film former containing resin plasticizer and solvent; colloidal dispersion of a resin in plasticizer containing more than 5 percent volatile content. |
| Oriel Window | A bay window projecting from a wall and supported on corbels or brackets. |
| Oriented Strand Board (OSB) | A type of particle panel product composed of strand-type flakes which are purposefully aligned in directions which make a panel stronger, stiffer, and with improved dimensional properties in the alignment directions than a panel with random flake orientat |
| Oriented Strand Board or OSB | A manufactured 4' X 8' wood panel made out of 1"- 2" wood chips and glue. Often used as a substitute for plywood. |
| Orifice | 1. An opening through which something may pass. 2. Attachment to the nozzle on the hose of a plastering machine, of various shapes and sizes, which may be changed to help establish the pattern of the plaster as it is projected onto the surface being plast |
| Original Contractor | In the law of mechanics liens, a contractor who contracts directly with an owner of real property. |
| Ormolu | A gilded bronze or gold-colored alloy of copper, zinc, and tin used to decorate furniture and make ornaments. |
| ormolu | Pale yellow gilt or bronzed metallic ware normally covered with a protective coat of clear lacquer. |
| Ornament | A thing used or serving to adorn; a decoration added to embellish. |
| Ornamental | Serving as an ornament; decorative. |
| Ornamental Facing | In masonry, a design formed by the laying of stone, brick, tile or other masonry units so as to produce a decorative effect. |
| Ornamental Metal | A detail that is added to a building constructed of metal, with the purpose of embellishment or decorating the structure. |
| Ornate | Elaborately adorned; highly decorated. |
| Orthogonal | Of or involving right angles. |
| Orthographic Projection | Projection of a single view of an object on a drawing surface that is perpendicular to both the view and the lines of projection; floor plans, elevations, and sections of buildings are orthographic projections. |
| Orthotropic | Having unique and independent properties in three mutually orthogonal (perpendicular) planes of symmetry; a special case of anisotropy. |
| OS&Y Valve | A type of valve, with external exposed threads supported by a yoke, indicating the open or closed position of the valve. |
| OSB | Oriented Strand Board. |
| Osborne & Little | English high-end fabric vendor. All exclusive fabrics, and very traditional. (90 Commerce Rd., Stamford, CT 06902) |
| Oscillation | A repeated back and forth movement, from one extreme to another, periodically from a maximum to a minimum. |
| Oscillograph | A device for recording oscillations. |
| Oscilloscope | A cathode ray tube that shows the changing voltage of an electrical signal as a curved line on a screen. |
| OSHA | Occupational Safety & Health Administration. |
| Osmosis | The passage of a solvent through a semi-permeable membrane into a more concentrated solution. |
| Ottawa Sand | A sand used as a standard in testing hydraulic cements by means of mortar test specimens; produced by processing silica rock particles obtained by hydraulic mining of the orthoquartzite situated in open pit deposits near Ottawa, Illinois; naturally rounde |
| ottoman | Available in cotton, silk, and synthetic yarns, it has a horizontal rib pattern, the stripes of which can be in different colors. It is hardwearing and suitable for upholstery. |
| Out of Phase | The state wherein a structure in motion is not at the same frequency as the ground motion; or where equipment in a building is at a different frequency from the structure. |
| Out of Square | The variation from true square. |
| Outdoor Exposure | Plastic pipe placed in service or stored so that it is not protected from the elements of normal weather conditions, the sun's rays, rain, air, and wind. |
| Outfall Sewer | A large sewer leading from the lower end of the collecting system to the place of disposal. |
| Outlet | 1.An electrical receptacle into which appliances may be plugged. 2. A way out; an exit. |
| Outlet Box | A box or container which houses an electrical outlet and its connections. |
| Outline Lighting | An arrangement of incandescent lamps or gaseous tubes to outline and call attention to certain features such as the shape of a building or the decoration of a window. |
| Outline Specifications | An abbreviated form of specifications normally produced with schematic design or design development drawings. |
| Outrigger | A structural member projecting from a main structure to provide additional stability or to support something, such as an outside scaffold. |
| Outrigger | An extension of a rafter beyond the wall line. Usually a smaller member nailed to a larger rafter to form a cornice or roof overhang. |
| Outrigger Scaffold | A work scaffolding supported on outrigger beams cantilevered out from the building or structure being worked on. |
| Outrigger, Flagpole | See Flagpole Outrigger. |
| Outside corner | The point at which two walls form an external angle, one you usually can walk around. |
| Outside Four Inches | The single tier of stretcher courses on the face of the wall. |
| Oven, Bake | See Bake Oven. |
| Oven, Convection | See Convection Oven. |
| Oven, Wall Mounted | See Wall Mounted Oven. |
| Ovendry Wood | Wood dried to a relatively constant weight in a ventilated oven at 102 to 105° C. |
| Overatomized | Dispersed too finely by use of excessive atomizing air pressure. |
| Overbank drainage | Water flow over top bank and down the slope. |
| Overcertification | The process of an architect or engineer certifying more than the proper amount to be paid to a contractor. |
| Overcoat | Second coat; topcoat. |
| Overcurrent | An electrical current that is in excess of the capacity of the wiring and devices. |
| Overcurrent Device | Any device that limits the current in a wire to a predetermined number of amperes. |
| Overflow | An opening to allow rainwater to overflow after it reaches a predetermined height, commonly 2 inches in the case of roof drains. |
| Overflow System | Surface water collection or draw-off arrangement. |
| Overglaze Decoration | A ceramic or metallic decoration applied and fired on the previously glazed surface of ceramic ware. |
| Overhand Work | A complete wall that is built from a scaffold that is located only on one side of the wall; the outside or farther face brickwork is laid by reaching over the wall. |
| Overhang | 1. The part of a roof that extends beyond the exterior walls of the building. 2. An overhead projection from the wall. 3. A leaning of the wall face away from the vertical. |
| Overhang | Outward projecting eave-soffit area of a roof; the part of the roof that hangs out or over the outside wall. See also Cornice. |
| Overhang Beam | A beam that is supported by two or more supports and has one or both ends projecting beyond the support. |
| Overhead | All of the indirect costs which can not be directly related to a unit of production and which must be included in the cost of the sale by some allocation method. |
| Overhead Concealed Closer | A door closer concealed in the head frame with an arm connecting with the door at the top rail. |
| Overhead Door | A door, commonly used in garages and warehouses, that opens upward from the ground. |
| Overimprovement | An improvement of excessive size or cost in comparison with similar properties particularly when it is not the highest and best use of the land. |
| Overlap | 1. The width of fresh paint covered by next layer. 2. Protrusion of weld metal beyond the bond at the toe of the weld. |
| Overlay | 1. A drawing on a thin layer of paper superimposed over a base drawing. 2. A thin layer of paper, paper, plastic, film, metal foil, or other material bonded to one or both faces of wood panel products or to lumber to provide a protective or decorative fac |
| Overlay | The addition of a layer over an existing pavement. Can be asphalt or crushed rock. Also referred to as resheeting. |
| Overlay Cabinet Construction | A method of building cabinets where the doors and drawer fronts are in front of the face frame. |
| Overload | Load greater than that for which system or mechanism was intended or designed. |
| Overload Protector | Device, either temperature, pressure or current operated, which will stop operation of unit if dangerous conditions arise; see Overcurrent Device. |
| Oversized Brick | A brick with dimensions greater than 2-1/2"x 3-1/2"x 7-1/2". |
| Overspray | See Drift, 2. |
| Overtopping | The passing of water over the top of a natural or man-made structure as a result of wave runup or surge. |
| Overvibration | Excessive vibration of freshly mixed concrete during placement causing segregation. |
| Ovolo | A quarter round molding. |
| Owner | 1. Any person or entity having some title or interest in a parcel of real property. 2. A person or entity who contracts for construction. |
| Owner's Overall Budget | A budget prepared by the owner of all of the project costs including land acquisition, construction, financing, professional fees, and all other incidental costs of the project. |
| Owner's Right to Stop Work | The owner has the right to stop the work of a construction contract only if the contract so provides and only for the reasons stated therein. |
| Owner-Builder | An owner of property who undertakes to construct improvements without the services of a general contractor. |
| OX, OXO, OXXO | Designations of the arrangement of sliding and fixed panels in sliding glass doors and windows; X indicates a sliding panel; O indicates a fixed panel; see also XO, XOO, XOOX. |
| Oxalic Acid | A poisonous strong organic acid, usually a solid white granular substance; used to dissolve iron rust stains on pool walls and floors, to clean iron rust from filter septa, and as a wood bleach. |
| Oxidation | The process of combining with oxygen. |
| Oxidize | To combine with oxygen; to become rusty. |
| Oxidized Sewage | Sewage which has been exposed to oxygen which causes organic substances to become stable. |
| Oxidizing Flame | A gas flame wherein the portion used has an oxidizing effect by an excess of oxygen. |
| Oxy-Acetylene | A mixture of oxygen and acetylene, used as a fuel in cutting or welding metals. |
| Oxygen | A colorless tasteless odorless gaseous element, occurring naturally in air, water, and most minerals and organic substances, and essential to plant and animal life. |
| Oxygen Cutting (OC) | A group of cutting processes wherein the severing or removing of metals is effected by means of the chemical reaction of oxygen with the base metal at elevated temperatures; in the case of oxidation-resistant metals the reaction is facilitated by the use |
| Oxygen-Acetylene Cutting | An oxygen-cutting process wherein the severing of metals is effected by means of the chemical reaction of oxygen with the base metal at elevated temperatures, the necessary temperature being maintained by means of gas flames obtained from the combustion o |
| Oxygen-Acetylene Welding | A gas welding process wherein coalescence is produced by heating with a gas flame or flames obtained from the combustion of acetylene with oxygen with or without the application of pressure and with or without the use of filler metal. |
| Oxygen-Arc Cutting | An oxygen-cutting process where in the severing of metals is effected by means of the chemical reaction of oxygen with the base metal at elevated temperatures the necessary temperature being maintained by means of an arc between an electrode and the base |
| Ozalid | Tradename of a system of drawing reproduction based on the ammonia vapor process; the prints consist of purple lines on a white background; other colors of line and background are also available. |
| Ozone | A form of oxygen, O3, a faintly blue unstable gas with a pungent odor and powerful oxidizing properties; used in disinfection, deodorization, oxidation, and bleaching. |