Definition excerpted from the ICBO Uniform Building Code: 1. Material of which no part will ignite and burn when subjected to fire. 2. Material having a structural base of noncombustible material as defined, with a surface not over 1/8" thick that has a flame spread rating of 50 or less. The term does not apply to surface finish materials.

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Noncalcerous Clays

Clays containing silicate of alumina, feldspar, and iron oxide.

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Nonprestressed Units

Concrete structural members in which the reinforcing steel is not subject to prestressing or post-tensioning.

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Nozzle

The part of a heating system that sprays the fuel of fuel-air mixture into the combustion chamber.

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Nonferrous

Metallic materials in which iron is not a principal element.

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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 A caulking material made from hemp fibers treated with tar.

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Occupational Health And Safety Administration (OSHA)

Outlines current indoor air quality guidelines for the workplace. https://healthymaterialslab.org/tool-guides/hml-resources

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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.

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OAC

Owner, Architect, Contractor. Used most often when referring to OAC meetings, or groups of project leads.

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Nylon

A synthetic plastic made from coal, tar, and water.

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Open Drainage

The removal of unwanted water by means of surface devices.

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Opaque Coatings

Coatings that completely obscure the color and much of the texture of the substrate.

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Oil-Based Paint

Paint composed of resins requiring solvent for reduction purposes.

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Off-Gassing

The production of gases from the chemical deterioration of a substance over time, and the release of gases from materials into the air. https://healthymaterialslab.org/tool-guides/hml-resources

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Octave

Interval between two sounds having a basic frequency ratio of two. The formula is 2n times the frequency, where n is the desired octave interval. The octave band frequency given in sound test results is usually the band center frequency, thus the 1000 Hz octave band encompasses frequencies from 707 Hz to 1414 Hz (n = ± 1/2). The 1000 Hz one-third-octave band encompasses frequencies from 891 Hz to 1122 Hz (n = ± 1/6).