Roof Online’s Glossary of Roofing Terms
Words that Start with the Letter “A”
Last updated July 7, 2020
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Abate: To remove material. The implication of the word is that the removal will require unusual attention that will cost more than a normal removal. Asbestos removal is an example.
Abatement: (1) A reduction or removal. (2) The removal of something that is against regulation or constitutes a nuisance or danger to others, such as noise or asbestos.
Absolute Humidity: The actual mass of water vapor in a given volume of air. Expressed as a ratio (such as g/kg).
Absorption: The process of taking in or soaking up (as of a liquid or energy) by chemical or physical action, typically gradually.
Accelerated Weathering: A laboratory testing technique in which materials are subjected to various simulated environmental conditions. These conditions are magnified or concentrated to determine the actual effects of natural weathering on the material in a relatively short amount of time.
Acid Etch: (1) The use of a strong acid to remove the surface of concrete, thus exposing the aggregate. (2) The use of a strong acid to etch the surface of material such as metal in order for that material to accept a primer or spray polyurethane foam.
Acid Rain: The precipitation of dilute solutions of strong mineral acids, formed by the mixing in the atmosphere of various industrial pollutants (primarily sulfur dioxide and nitrogen oxides) with naturally occurring oxygen and water vapor.
Acoustical Deck: Metal deck in which the panel or pan is perforated to allow sound to pass through and be trapped in acoustical absorbing material or cavity on the top side of the deck.
Acrylic Coating: A coating system with an acrylic resin base. Acrylic coatings are water-based and cure through evaporation.
Acrylic Resin: Any of a group of thermoplastic resins formed by polymerizing the esters of amides of acrylic or methacrylic acid: used chiefly where transparency is desired, as in the methacrylate resins Lucite and Plexiglas. Often used as a base for coating systems.
Active (Metal): Subject to corrosion in the presence of moisture or a "noble" metal. The activity series of metals lists the metals so as to to predict the products and reactivity of the metals with hydrogen-ion sources such as acids and water. The metals are listed in a decreasing order of their reactivity, with the most reactive metal at the top of the list. The more nonreactive metals are found at the bottom of the list. The list of the activity series of metals: Lithium (Li) Potassium (K) Strontium (Sr) Calcium (Ca) Sodium (Na) Magnesium (Mg) Aluminum (Al) Zinc (Zn) Chromium (Cr) Iron (Fe) Cadmium (Cd) Cobalt (Co) Nickel (Ni) Tin (Sn) Lead (Pb) Antimony (Sb) Arsenic (As) Bismuth (Bi) Copper (Cu) Mercury (Hg) Silver (Ag) Paladium (Pd) Platinum (Pt) Gold (Au). The first five elements (Li through Na) are highly reactive metals. These elements displace hydrogen from water, acids, and steam, and form hydroxides. The four metals from Mg through Cr are known as active metals. The next six metals (Fe through Pb) displace hydrogen from acids only. The metals from Antimony to Copper combine with oxygen to form oxides, and cannot displace hydrogen. The last five elements (Hg through Au) are found free in nature with little oxidation.
Adhere: For one surface to bond with another through the action of a molecular force in the area of contact.
Adhesion: The state of adhering.
Adhesive: A substance used to bond two surfaces together.
Adhesive Failure: Loss of the ability of an adhesive to bond with a surface.
Adiprene: A polyurethane synthetic rubber notable for its strength and abrasion-resistance.
Adjuster: A person who works in the insurance field evaluating property damage.
Adsorbent: Material that is capable of collecting and binding substances or particles on its surface without chemically altering them.
Aesthetic: Having an attractive or acceptable appearance. Usually used in roofing to indicate that something is not necessarily required for a roof to function properly.
AFA: American Fiberboard Association
A-Frame: A rigid structure in the shape of an "A". Uses the structural stability of the triangle to provide strength in construction.
Aggregate: (1) crushed stone, crushed slag, water-worn gravel, crushed lava rock or marble chips used for surfacing a built-up roof; (2) any granular mineral material.
Air Barrier: A material used to prevent the flow of air through a building component, typically preventing outside air from flowing in and inside air from flowing out.
Air Barrier System: Combination of components used to create a state of air tightness throughout the building envelope.
Air Blown Asphalt: Asphalt produced by blowing air through molten asphalt. This procedure is used to raise the softening point and modify other properties of the asphalt.
Air Changes Per Hour (ACH): Number of times per hour a volume of air, equivalent to the volume of space, enters that space.
Air Exchange Rate: The rate at which indoor air is replaced by outside air in a given space.
Air Handling Unit: Equipment that includes a fan or blower, regulator controls, condensate drain pans, heating and/or cooling coils, and air filters.
Air Lance: A device used to direct a stream of pressurized air. Used to remove debris or unwanted accumulations. Also used to test the integrity of membrane seams.
Air Leakage: The uncontrolled flow of interior air through holes in the building envelope.
Air Plenum: Any space used to convey air in a building, furnace or structure. The space above a suspended ceiling is often used as an air plenum.
Albedo: Also known as solar reflectance; the ability to reflect sunlight. It is expressed either as a decimal fraction or a percentage. A value of 0 indicates that the surface absorbs all solar radiation, and a value of 1 represents total reflectivity.
Algae Discoloration: A type of roof discoloration, characterized by black stains and streaks, caused by the cyanobacteria Gloeocapsa magma. Also called fungus growth.
Alkalinity: The capacity of a sample of water to neutralize an acid solution.
Alligatoring: The cracking of the surface bitumen on a built-up roof due to the loss of volatile oils and oxidation from UV exposure over time. The process produces a pattern of cracks that is said to resemble an alligator’s skin.
Alternative Energy: Energy from a source other than the conventional fossil-fuel sources of oil, natural gas and coal (i.e., wind, running water, the sun). Also referred to as "alternative fuel."
Aluminized Steel: Sheet steel with an aluminum coating on the surface which enhances the steel’s ability to withstand weathering.
Aluminum: a silvery white member of the boron group of chemical elements. It has the symbol Al, with atomic number 13. It is not soluble in water under normal circumstances.
Aluminum is noted for its low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural components made from aluminum and its alloys are vital to the aerospace industry, as well as to many areas of construction and other manufacturing. The most useful compounds of aluminum, at least on a weight basis, are the oxides and sulfates.
Aluminum is the most abundant metal, and the third most abundant element after oxygen and silicon, in the Earth's crust. It makes up about 8% by weight of the Earth's solid surface. Aluminum metal is too reactive chemically to occur natively. In combination it is found with 270 different minerals. The chief ore of aluminum is bauxite. Despite its prevalence in the environment, aluminum salts are not known to be used by any form of life. In keeping with its pervasiveness, it is well tolerated by plants and animals.
Ambient Air: The surrounding air.
Ambient Temperature: The temperature of the surrounding air.
American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE): ASHRAE is an international organization that establishes standards for the uniform testing and rating of heating, ventilation, air conditioning, and refrigeration equipment. It also conducts related research, disseminates publications, and provides continuing education to its members.
Anchor Bolt: A bolt with its head embedded in masonry or concrete and its threaded portion exposed. Used to attach various things to a structure.
Angled Fasteners: Nails and staples that are driven into the roofing deck at an angle, not perpendicular to the deck.
Anneal: To heat and slowly cool a material (glass or metal) in order to remove existing internal stresses, thereby toughening it.
Anodic: When two metals are connected in an electrolyte, they will form a galvanic cell, with the higher metal in the galvanic series being the anode. The anodic metal will oxidize and produce an electrical current which protects the other (cathodic) metal from corrosion.
Anodized Aluminum: Aluminum that has been coated by an electrolytic process to produce an oxide film that is corrosion-resistant.
ANSI: American National Standards Institute
Antioxidant: A substance which inhibits or prevents oxidation.
APP: Atactic Polypropylene
Application Rate: The rate at which a material is applied per unit area.
Apron Flashing: A term used for a flashing located at the juncture of the top of a sloped roof and a vertical wall, chimney or steeper-sloped roof.
Architectural Panel: A metal roof panel, typically a double standing seam or batten seam; usually requires solid decking underneath and relies on slope and gravity to shed water.
Architectural Shingle: Shingle that provides a dimensional appearance. Also see Dimensional Shingle and Laminated Shingle.
Area Divider: A flashed assembly, usually extending above the surface of the roof, that is anchored to the roof deck. It is used to relieve thermal stresses in a roof system where an expansion joint is not required, or to separate large roof areas.
Asbestos: An incombustible fibrous mineral form of magnesium silicate formerly used for fireproofing and sometimes used for the reinforcement of roofing materials.
ASC: Associated Specialty Contractors
ASHRAE: American Society of Heating, Refrigerating & Air-Conditioning Engineers, Inc.
Asphalt: A dark brown to black cementitious material in which the predominating constituents are bitumens, which occur in nature or are obtained in petroleum processing. Asphalt can be refined to conform to various roofing grade specifications:
Dead-Level Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type I. This asphalt is for use in roofs which do not exceed a ¼ in 12 slope (2%).
Flat Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type II. This asphalt is for use in roofs which do not exceed a ½ in 12 slope (4%).
Special Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type IV. This asphalt is for use in roofs which do not exceed a 6 in 12 slope (50%).
Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type III. This asphalt is for use in roofs which do not exceed a 3 in 12 slope (25%).
Asphalt Emulsion: A mixture of asphalt particles and an emulsifying agent, such as bentonite clay, and water.
Asphaltene: Crude oil components of high molecular weight precipitated by a low-boiling paraffin solvent at a specified temperature and solvent-to-crude-oil ratio.
Asphalt Felt: An asphalt-saturated and/or an asphalt-coated felt membrane. (See also "Felt")
Asphalt Mastic: A mixture of asphaltic material and mineral aggregate that becomes fluid when heated but requires mechanical manipulation to apply when cool.
Asphalt Primer: Asphalt thinned by mixing with a solvent; typically hand-applied to a surface to ensure the adhesion of hot asphalt. Also see "Primer".
Asphalt Roof Cement: The proper name for Plastic Cement and Flashing Cement. Asphalt roof cement consists of solvent-based bitumen, mineral stabilizers, and other fibers (sometimes asbestos). Asphalt roof cement is categorized by ASTM standard D 2822-91 (1997) or for non-asbestos, ASTM standard D 4586-93.
Flashing Cement can be used on vertical surfaces and has a high softening point, low ductility and conforms to the requirement of ASTM Specification D 312, Types II or III; or Specification D 449, Type III.
Plastic Cement is for use on low-slope surfaces, conforms to ASTM Specification D 312, Type I; Specification D 449, Types I or II; or Specification D 946. Plastic Cement is self-sealing, adhesive and ductile and is classified by ASTM Standard D 2822-91 Asphalt Roof Cement, and D 4586-92 Asphalt Roof Cement, Asbestos-Free, Types I and II.
Asphalt Spreader: A wheeled device used to apply hot asphalt at a controlled rate.
ASTM International: (until 2001 the American Society for Testing and Materials or ASTM) an international organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services.
Atactic Polypropylene: A group of high molecular weight polymers formed by the polymerization of propylene. It can be mixed with asphalt to produce APP modified bitumen.
Attic: The area between the ceiling and the roof deck of a steep-sloped roof.