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A
Access door or panel:
A means of access for the inspection repair, or service of concealed systems, such as air conditioning equipment.

Active leaf:
In a double-leaf door, the leaf to which the latching or locking mechanism is attached.

Admixture:
An ingredient other than cement, aggregate, or water that is added to a concrete or mortar mix to affect the physical or chemical characteristics of the concrete. The most common admixtures affect plasticity.

Air conditioner:
A system that may control temperature, humidity, and or the cleanliness of air within an enclosure.

Air conditioning:
The process of controlling the temperature, humidity, and cleanliness or air and of distributing it within an enclosure.

Air diffuser:
An outlet in an air-supply duct for distributing and blending air in an enclosure. Usually, a round, square or rectangular unit mounted in a suspended ceiling.

Air entraining agent:
An admixture for concrete or mortar mixes which causes minute air bubbles to form within the mix. Air entrainment is desirable for workability of the mix and prevention of cracking in the freeze/thaw cycle.

Allowable bearing valve, allowable soil pressure:
The bearing capacity of a soil, in pounds per square foot (psf), determined by its characteristics such as shear, compressibility, water content, and cohesion. The higher the allowable bearing valve of a soil, the smaller the footing required to support a structural member.

Allowable load:
The ultimate load divided by a safety factor.

Ampere:
The electromotive force required to move one volt of electricity across an ohm of resistance. A measure of electrical current.

Anchor bolt, foundation bolt, hold-down bolt:
A threaded bolt, usually embedded in a foundation, for securing a sill, framework, or machinery.

Apron:
(1) A piece of finished trim placed under a window stool.
(2) A slab of concrete extending beyond the entrance to a building, particularly at an entrance for vehicle traffic.
(3) The piece of flat wood under the base of a cabinet.
(4) Weather protection paneling on the exterior of a building.
(5) A splashboard at the back of a sink.
(6) At an airport, the pavement adjacent to hangers and appurtenant buildings.

Ash dump:
An opening in the bottom of a firebox or fireplace into which ashes are swept, falling into an asphalt below.

Asphalt felt:
Felt impregnated with asphalt and used in roofing and sheathing systems.

Asphalt shingles, composition shingles, strip slates:
Roofing felt, saturated with asphalt and coated on the weather side with a harder asphalt and aggregate particles, which has been cut into shingles.

Astragal:
A molding attached to one of a pair of doors or casement windows to cover up the joint between two stiles.