Abutment - The lateral supporting structure of an arch, bridge or similar pressure; that part of a pier or wall from which an arch springs, specifically the support at either end of an arch, beam or bridge; that part of a structure which takes the thrust of a beam, arch, vault, truss or girder; the part of a bridge that supports the end of the span and prevents the bank from sliding under it; a foundation that carries gravity and also thrust loads.

A/C - An abbreviation for air conditioner or air conditioning.

A/C - An abbreviation for alternating current.

A/C Circuit - (Alternating Current) - The flow of current through a conductor first in one direction then in reverse. It is used exclusively in residential and commercial wiring because it provides greater flexibility in voltage selection and simplicity of equipment design.

A/C Condenser - The outside fan unit of the Air Conditioning system. It removes the heat from the freon gas and "turns" the gas back into a liquid and pumps the liquid back to the coil in the furnace.

A/C Disconnect - The main electrical ON-OFF switch near the A/C Condenser.

Accelerator - Any material added to stucco, plaster or which speeds up the natural set.

Accordion Folding Door - A folding, hinged, or creased door with rollers, which run along a track.

Accordion Partition - A folded, creased, or hinged interior dividing wall.

Acre - A plot of land 180 by 242 feet is equal to one acre or 43,560 square feet.

Active Door - In a pair of doors, the leaf that opens first and the one to which the lock is applied.

Actual Dimensions - The exact measurements of a piece of lumber. For instance, a 2x4 (nominal dimensions) is actually 1 1/2 inches thick by 3 1/2 inches wide.

Adfreezing - Means the adhesion of soil to a foundation unit resulting from the freezing of soil water.

Aerator - The round screened screw-on tip of a sink spout. It mixes water and air for a smooth flow.

A-Frame - A roof shape with a very steep pitch forming a gable or "A" shape.

Aggregate - A mixture of sand and stone and a major component of concrete.

Air Barrier System - The assembly installed to provide a continuous barrier to the movement of air.

Air-Conditioning - The process of treating air to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the comfort requirements of the occupants of the conditioned space.

Air Diffuser - Air distribution outlet or grille designed to direct airflow into desired patterns.

Air Gap - Means the unobstructed vertical distance through air between the lowest point of a water supply outlet and the flood level rim of a fixture or device into which the outlet discharges.

Air Source Heat Pump - A heating-cooling unit that transfers heat in either direction between the air outside and inside a home.

Air Space - The area between insulation facing and interior of exterior wall coverings. Normally a 1" air gap.

Alcove - A recessed space connected at the side of a larger room.

Allen Wrench - An L-shaped hexagonal rod designed to fit into a hexagonal hole in a bolt head; also called an Allen Key.

Allowance(s) - A sum of money set aside in the construction contract for items, which have not been selected and specified in the construction contract. For example, selection of tile as a flooring may require an allowance for an underlay material, or an electrical allowance which sets aside an amount of money to be spent on electrical fixtures.

Ambient Temperature - The temperature, usually of the air, that surrounds operating equipment.

American Wire Gauge - A standard measure, which represents the size of wire. The larger the number, the smaller the wire. Abbreviated AWG.

Amortization - A payment plan by which a loan is reduced through monthly payments of principal and interest.

Anchor Bolts - Bolts to secure a wooden sill plate to concrete, or masonry floor or wall.

Angle Iron - L-shaped metal piece commonly used as a masonry lintel.

Angle of Repose - A measurement of the steepest angle of a surface at which loose material such as soil will remain in place rather than sliding or crumbling.

Angle Stop - A shutoff valve between the water pipes and a faucet. Its inlet connects to the water supply pipe in a wall, and its outlet angles up 90 degrees toward the faucet. These are usually used to shut off water to a fixture in case of an emergency repair rather than daily usage.

Annealing - In the manufacturing of float glass, it is the process of controlled cooling done in a lehr to prevent residual stresses in the glass. Re-annealing is the process of removing objectionable stresses in glass by re-heating to a suitable temperature followed by controlled cooling.

Annual Percentage Rate (APR) - Annual cost of credit over the life of a loan, including

interest, service charges, points, loan fees, mortgage insurance, and other items.

Anode Rod - A sacrificial rod installed in a water heater that protects the tank from corrosion, helping to extend the life of the tank.

Appliance - A device to convert fuel into energy and includes all components, controls, wiring and piping required to be part of the device by the applicable standard referred to in the Ontario Building Code

Appraisal - An expert valuation of property.

Apron - A trim board that is installed beneath a window sill.

Apron Flashing - A term used for a flashing located at the juncture of the top of the sloped roof and a vertical wall or steeper-sloped roof.

Aquastat - A thermostat that controls the water temperature in a boiler.

Architect - An Architect is a licensed individual who leads a design team in the planning and design of buildings and participates in oversight of building construction .

Architectural Technologist - The Architectural Technologist , also known as a Building Technologist, provides building design services and solutions and is trained in architectural technology, building design and construction.

Area Wells - Corrugated metal or concrete barrier walls installed around a basement window to hold back the earth.

Armoured/BX Cable - Cable with a flexible metal covering that is often used with appliances.

As-Built Drawing - A drawing detailing the works as completed, detailing all changes made from the original drawings.

Assessment - A tax levied on a property, or a value placed on the worth of a property.

Assumption - Allows a buyer to assume responsibility for an existing loan instead of getting a new loan.

Astragal - A moulding, attached to one of a pair of swinging double doors, against which the other door strikes.

Atrium - An open court within a building.

Attic Access - An opening that is placed in the drywalled ceiling of a home providing access to the attic. 

Attic or Roof Space - The space between the roof and the ceiling of the top storey or between a dwarf wall and a sloping roof.

Attic Ventilators - In houses , screened openings to ventilate attic spaces.

Awning - A roof-like covering to shelter people or protect parts of a building from the effects of the sun or rain.

Awning Window - A window hinged along the top edge.

Axial Force - A push (compression) or pull (tension) ·acting along the length of a member,
expressed in kilonewtons (pounds).

Axial Stress - The axial force acting at a point along the length
of a member divided by the cross-sectional area of a member, expressed in kilopascals (pounds per square inch).