Access, Hatch – See “Hatch”.

Aerated Concrete – A lightweight concrete containing minute air filled voids that account for a large part of its mass. Its sound and heat transmission properties are lower than those of ordinary concrete. See “Cellular Concrete”.

Aggregate – Material, such as gravel, broken stone or sand, with that, cements and water is mixed to form concrete. Crushed stone is usually designated as coarse aggregate and sand as fine aggregate.

Air-Conditioning – Defined under “Heating”.

Air-Dried – A condition of lumber resulting from seasoning under natural atmospheric conditions.

Air Duct – A pipe, tube or passageway for conveying air, normally associated with heating, ventilating and air conditioning.

Air-Entrained Concrete – Concrete in that air in the form of minute bubbles has been occluded during the mixing period as a result of the use of an air-entraining agent as an admixture.

Air Gap – Defined under “Plumbing Terms”.

Air Pocket – A space or void created by trapped air that accidentally occurs in concrete work or in a pipeline.

Air Space – A cavity or space in walls, windows or other enclosed parts of a building between various structural members.

Air Supported Structure – A Structure consisting of a pliable membrane that achieves and maintains its shape and support by internal air pressure.

Airway – The space left been roof insulation and roof decking to allow free movement of air.

Air Well – A space within the building, enclosed by walls, partially or totally open to the outside air at the roof and intended solely as a means of ventilation for bathrooms, kitchens, and like service rooms.NHD

Alternating Current – Defined under “Electrical Terms”.

Amenity Area – An area or areas within the boundaries of a project intended for recreational purposes that may include landscaped site areas, patios, common areas, communal lounges, swimming pools and areas used for similar purposes.

Ampere – Defined under “Electrical Terms”.

Anchor Bolt – A steel bolt used to secure a structural member against uplift. It is usually deformed at one end to ensure a good grip in the concrete or masonry in that it is embedded.

Angle Bead – A small moulding placed at an external angle formed by plastered surfaces in order to preserve the corner from accidental fracture.

Angle Iron – An L-shaped steel section frequently used to support masonry over a window or door opening.

Anhydrous Lime – Quicklime.

Annual Growth Ring – The ring seen on the transverse section of a piece of wood indicating yearly growth. Also referred to as a grain.

Apartment – A room or suite of rooms used as living quarters. A dwelling unit of a multi-family house. See “Dwelling, multiple”.

Apartment Building – A type of multiple dwelling comprising three or more dwelling units with shared entrances and other essential facilities and services with shared entrances and other essential facilities and services and with shared exit facilities above the first storey.

Apron – A plain or moulded finish piece below the stool of a window, installed to cover the rough edge of the wall finish. Also the extension of the concrete floor of a garage or other structure beyond the face of the building.

Arch – An arch is a mechanical arrangement of building materials that are put together, generally along a curved line, in such a way that, supported by piers, abutments or walls, they carry the weight and resist the pressure.

Arch Brick – a brick having a wedge shape, also one with a curved face suitable for wells and other circular work.

Architrave – Mouldings around openings and certain other locations to conceal joints or for decorative purposes.

Area – The surface within specific boundaries.

Area of Building – The maximum projected horizontal area of the building at or above grade within the outside perimeter of the exterior walls or within the outside perimeter of exterior walls and the center line of fire walls.

Area, Floor – The space on any storey of a building between exterior walls and required firewalls, including the space occupied by interior walls and partitions, but not including exits and vertical service spaces that pierce the story.

Area, Gross – In reference to a structural unit, shall mean the total area within the outer periphery of any section perpendicular to the stress to be resisted.

Area, Net – In reference to a structural unit, shall mean the minimum effective load-bearing area of the material composing the unit, included in any section perpendicular to the direction of the stress to be resisted.

Area, Net Room – The floor area of a room measured from finished wall to finished wall.

Areaway – An open sub-surface space, adjacent to a building, used to admit light or air, or as a means of access to an area or floor level below grade.

Artificial Stone – A special concrete unit, sometimes artificially coloured, intended to resemble natural stone, made by mixing chippings and dust of natural stone with Portland Cement and water. This mixture is placed in moulds and cured before use.

Asbestos Cement – A fire-resisting weatherproof building material made from Portland Cement and asbestos. It is manufactured in various forms such as plain sheets, corrugated sheets, shingles, pipes, etc.

Ashlar – Defined under “Stonework, Kinds of”.

Asphalt – A dark substance that is insoluble in water and used extensively in building for waterproofing, roof coverings, in the manufacture of shingles and floor tiles and in paints.

Astragal – A small plain or ornamental moulding.

Attic or Roof Space – The space between the top floor ceiling and roof, and between a dwarf partition and sloping roof.

Awning Window – Defined under “Window Types”.