Glossary – O

Oil Tank:   A tank used to supply oil burning appliance such as a furnace, boiler or water heater. Oil tanks are frequently buried underground.

On Center ( Abbreviated By O.C.):   The measurement of spacing for framing members, fasteners, etc., which designate the distance from the center of one member or component to the center of the next. Also called center to center spacing.

On-Site Water Supply Quantity:  Water quantity is the rate of flow of water. Refer to water flow – 3 G.P.M. minimum.

Open Beam Construction:   Frame construction in which the ceiling and ceiling joists are eliminated, leaving the beams and deck of the roof exposed and treating them as an element of the interior finish of the room. In this type of construction the structural members or the roof are usually heavier and may be on wider centers.

Open Valley:   Method of valley construction in which shingles on both sides of the valley are trimmed along a chalk line snapped on each side of the valley. Shingles do not extend across the valley. Valley flashing is exposed.

Open Web Joists:  Lightweight, parallel trusses of prefabricated metal.

Organic Felt:   An asphalt roofing base material manufactured from cellulose fibers.

Oriel Window:   A window that projects from the outer face of a wall, especially from an upper story, and is supported by brackets or a cantilever, as distinguished from a bay window, which is at first-floor level and usually supported by a foundation.

Outward:   Directed toward the outside, usually at a 90 degree angle (perpendicular to) the exterior surface.

Overhang:   That portion of the roof structure that extends beyond the exterior walls of a building.

Oversized Fuse:   A fuse which does not provide adequate protection for an electrical circuit.