Roof Online’s Glossary of Roofing Terms

By Roof Online Staff • Updated May 1, 2024

(On the way to being the most complete roofing glossary we’ve seen on the internet. Please bear with us.)

This is a glossary of roofing terms. It also contains quite a few words that aren’t necessarily specific to roofing which can still be relevant to roofs. We aim to be comprehensive, so if you are looking for a definition and can’t find it, please let us know.

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M – Roofing Terms that Start with “M”

AAMA: American Architectural Manufacturers Association (now the Fenestration & Glazing Industry Alliance)

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. 

ACI: American Concrete Institute

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.

ACIL: American Council of Independent Laboratories

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: 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) Palladium (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.

AdhesiveA 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.

AGC: Associated General Contractors of America

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.

AHA: American Hardboard Association

AIA: American Institute of Architects

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 AsphaltAsphalt 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.

AnodicWhen 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.

ANSIAmerican National Standards Institute

Antioxidant: A substance which inhibits or prevents oxidation.

APA: American Plywood Association (Now known as the Engineered Wood Association).

APPAtactic 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 ShingleShingle 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.

ARMA: Asphalt Roofing Manufacturers Association

ASA: American Subcontractors Association

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

ASCE: American Society of Civil Engineers

ASHI: American Society of Home Inspectors

ASHRAEAmerican Society of Heating, Refrigerating & Air-Conditioning Engineers, Inc.

AsphaltA 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 CementThe 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 PolypropyleneA 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.

AWPA: American Wood Protection Association

AWS: American Welding Society

Backer RodA cylindrical piece of foam material installed in a gap or joint between building materials to provide a substrate for building sealant.

Back Nailing: The technique of fastening the back or top side of a ply of roofing felt, shingle, or other component in a roof system so that the fasteners are covered by the following ply or course and not left exposed to the weather.

Back Surfacing: A fine mineral material applied to the back side of roofing materials such as asphalt shingles or roll roofing to keep the materials from sticking together while packaged.

Back Water Lap: A lap installed in such a way that it obstructs the flow of water.

Bake-out: A method of reducing future VOC emissions from furniture or construction materials in which a building is heated after construction or refurnishing in an attempt to accelerate those emissions before occupancy.

Balanced System: A ventilation system where 50% of the required ventilating area is provided by vents located in the upper portion of the roof with the balance provided by under-eave or soffit vents.

Balcony: A railed platform projecting from a wall.

Ballast: A material installed over the top of a roof membrane to help hold it in place. Ballast is loose-laid and usually consists of stones or pavers.

Balustrade: A railing system including a rail or rails and the supporting posts, or balusters.

Bargeboard: A board, often ornamental, which conceals the projecting roof timbers at gable ends.

Bar Joist: Common term for “Open Web Steel Joist” (which see).

Barrel Roof: A curved roof that has the appearance of a section of the side of a barrel.

Base Coat: The first coat in a multi-coat application.

Base Flashing: Those parts of a roof which are attached to the field membrane and seal the system at vertical intersections, such as at roof/wall and roof/curb junctures. (See also Flashing).

Basement: The below-grade and foundational part of a building containing occupiable space.

Base Ply: The primary layer of roofing material in a roof system. (See also Base Sheet).

Base Sheet: An impregnated and/or coated felt attached to the deck, insulation, or cover board and used as the first ply in some built-up and modified bitumen roof systems.

Batt: A roll or sheet of fibrous material used for stuffing or insulation. See Batt Insulation.

Batten: (1) A strip of solid material such as wood, metal, or plastic usually fastened to the structural deck for use in attaching roof system components such as tiles or metal panels; (2) (Also Batten Bar or Batten Strip) A similar strip of solid material which is used to fasten the roof membrane and/or base flashing in place.

Batten Seam: A seam in a metal roof which is formed around a batten.

Batt Insulation: Fibrous insulation manufactured as sheets or rolls. Typically made from fiberglass or stone wool.

Bay: The space between certain structural components, such as between columns, posts, joists, or rafters.

Beadboard (Insulation): A common term for expanded polystyrene (EPS) foam board insulation.

Beam: A structural member, such as a joist or a rafter, with the primary function of carrying transverse loads.

Bearing Plate: A steel plate placed under a structural member in order to distribute the force on the member to its support.

Bearing Wall: A wall that supports the weight of structural elements above itself in addition to its own weight.

Beaufort Scale: (Beaufort Wind Force Scale) A measurement system that relates wind speed to observable conditions.

Beaverboard: Wood fiberboard.

Bell Roof: A roof with a cross-section similar to that of a bell.

Below Grade Waterproofing: Any of various waterproofing systems applied on below grade walls, such as basement walls, that are intended to resist moisture penetration due to hydrostatic pressure from the surrounding soil, and to last the life of the structure.

Belvedere: Any structure situated so as to provide access to a scenic view. Typically placed on a hilltop or upper portion of a building. 

Bentonite: A highly absorbent clay, which expands when wet, derived from volcanic ash. Often used in below grade waterproofing or in roof coating emulsions.

Bermuda Seam: metal roof in which the roofing panels are installed perpendicular to the roof slope so that the roof has a step profile.

Bird Bath: Trivial amounts of standing water on a roof that completely evaporate relatively quickly. (See also Ponding).

Bird Screen: A mesh, usually wire, installed across vents or other openings in order to prevent birds from entering a building

Bird Stop: A strip of material such as shaped metal, tile, or foam installed under the first course of a tile roof to prevent birds from nesting under the tiles, as well as to align the first course of tile with the subsequent courses.

Bitumen: A general term for mixtures of high molecular weight hydrocarbons and other substances which occur either naturally or as a product of coal or petroleum processing. In roofing and waterproofing, “bitumen” typically refers to asphalt or coal tar pitch.

Bitumen-Stop: A dam constructed by extending a ply in a built-up roof beyond the other field plies and folding it back onto the top of the system.  Its purpose is to prevent bitumen from leaking down the side of the building or into penetrations within the system.

Blackberry: A small bubble in the flood coat of a built-up roof.

Blanket Insulation: See Batt Insulation.

Bleeder Strip: See Rake-Starter Strip.

Bleeding: The migration of a coloring substance from one material into an adjacent material.

Blind Nailing: The use of fasteners such that they are not visible or exposed to the weather in the finished system. See also Back Nailing.

Blind Rivet: Also called a “pop rivet”. A mechanical fastener with an expandable shank used when only one side of the material to be fastened is accessible. Typically used for securing light-gauge metal components such as flashing or gutters.   

BlisterA pocket of air and/or water vapor trapped between layers of felt or membrane. Blisters typically develop from lamination voids within the system and grow due to thermal expansion and contraction of the gasses within them.

Blocking: Wood components built into a roof assembly and used to strengthen the deck around an opening, to support a curb, or for use as a nailer for the attachment of membranes or flashing.

Bloom: See Efflorescence.

Blower Door: A test equipment assembly used to measure the air-tightness of buildings or ductwork, and to identify locations of air leakage. 

Blowing Agent: A substance used to produce a cellular structure in a variety of materials that harden after application.

Blown Asphalt: See Air Blown Asphalt.

Blueberry: See Blackberry.

Board-foot: A unit of measure of volume equaling 12 inches by 12 inches by 1 inch. (1/12th of a cubic foot.) 

BOCA: Building Officials and Code Administrators International, Inc.

Bolt: A log section cut to size for processing in a shingle brake.

BOMABuilding Owners and Managers Association International

Bond: 1) The force or forces holding two components in positive contact) As a surety, a legally binding promise by one party to assume the obligations of a second party should the second party fail to fulfill a contractual obligation to a third party.

Bonding Agent: A chemical substance used to create a bond between two surfaces.

Boot: A piece of flexible pre-formed material installed in order to seal the roof at a penetration.

Borescope: An optical inspection device used to view the inside of a structure through a hole.

Box Gutter: A gutter, usually rectangular, designed to be installed between two parallel surfaces, as between the edge of a roof and a parapet wall. Also called an internal gutter.

Brake: A device used to bend, shape, or form metal.

Brand: An airborne ember produced by a fire.

Breaking Strain: Percent elongation at which a specimen fails due to tensile force.

Bridging: 1. A characteristic of unsupported areas of membrane at junctures between roof components. 2. In asphalt shingle roofing, a re-roofing technique that typically involves installing metric-sized shingles over standard-sized shingles in a manner that allows the new course of shingles to overlay two courses of the existing shingles.

British Thermal Unit (BTU): Approximately, the quantity of heat energy required to raise the temperature of one pound of water one degree Fahrenheit. Approximately 1055 joules.

Brooming: The use of a broom or squeegee to embed a ply of roofing material into hot bitumen or adhesive, eliminating voids and ensuring adhesion.

Buck: A lap in which the down-slope component laps the up-slope component, causing the edge of the material to obstruct the flow of water. This type of lap is said to “buck water”. See also “Back Water Lap”. 

Buckle: Or BucklingA tented displacement of a roof membrane, typically at insulation and deck joints.

Building Code: A set of rules specifying the minimum acceptable standards for safety in building construction.

Building Envelope: Also referred to as “building shell” or “building enclosure”. The exterior surface which physically separates the interior and exterior environments of a building. It includes the walls, windows, roof, and foundation floor.

Building Inspector: Government official employed to assure compliance with the building and related codes that are in force in the jurisdiction.

Building Paper: A heavy-duty and water-resistant paper used as a vapor barrier and to provide weatherproofing at the sheathing in frame construction.

Built-Up Roof: Often called “BUR”. A flat or low-sloped roof comprising multiple layers of bitumen and reinforcement plies.

Built-Up Roof Membrane: A roof membrane comprising multiple layers of bitumen, which serves as the waterproofing component, with plies of reinforcement fabric installed between each layer. The reinforcement material typically consists of bitumen-saturated or coated cellulose, fiberglass, or polyester felt. A protective surfacing is normally applied consisting of aggregate, emulsion coating, or cap sheet.

Bulb-Tee: A type of steel reinforcing member used in the construction of pre-stressed, poured gypsum decks.

Bulkhead: A structure above the roof of a building which encloses a stairwell or other opening.

Bundle: An individual package of shingles or shakes.

BUR: An acronym for Built-Up Roof.

Butadiene: A colorless, highly flammable hydrocarbon, C4H6, derived from petroleum and used in the manufacture of synthetic rubber.

Butt Edge: The lower edge of a shingle.

Butt Joint: A joint between two separate, adjacent pieces of material, such as insulation boards.

Butyl: A hydrocarbon radical, C4H9, with a rubber-like consistency, formed from the copolymerization of isobutylene and isoprene and used primarily in sealants and adhesives.

Butyl Rubber: A butyl-based synthetic elastomer.

Butyl Tape: A butyl-based sealant tape.

By-product: A product, other than the principal product, generated as a consequence of an industrial process or chemical reaction.

Half-gabled: See Shed Roof.

Half-hipped Roof: See Gambrel Roof.            

Half Principal: A principal rafter that does not go all the way to the ridgepole and is supported by a purlin at its upper end.

Half Slating: See Open Slating.

Half Span Roof: A lean-to roof. A roof that slopes in only one direction, supported by a wall that rises above the roof at the high end.

Half Truss: A jack truss shaped like half of a normal truss, with a vertical member at the high end.

Hammer Beam: Either of a pair of short horizontal members at the top of opposite walls which support a principal rafter in place of a tie beam.

Hammer-beam Roof: A decorative, timber-framed roof supported by hammer beams.

Hammer Brace: A curved brace that supports the interior end of a hammer beam.

Hand-tabbing: An installation technique for improving the performance, appearance, and wind resistance of asphalt shingles, in which roofing cement is applied in spots under the edge of the shingles.

Hatch: Roof Hatch. An opening in a roof with a weathertight, hinged cover which provides access to a roof from the interior of the building.

Header: In framing, a horizontal structural member at the top of an opening such as a door or a window.

Head Flashing: The flashing installed at the top of a window or door to direct water out and away from the opening in the wall.

Headlap: The minimum distance that the topmost course or ply of a multiple-layer roofing application, such as shingles or felts, overlaps the bottommost course or ply.

Heat Aging: A laboratory testing technique in which materials are subjected to elevated temperatures over time to accelerate age-related deterioration.

Heat and Smoke Vents: Covered openings in a roof that function as an active fire protection measure, intended to open during a fire and vent out the heat and smoke resulting from a fire within the building.

Heating Degree Day (HDD): A measurement intended to quantify the energy requirements of heating a building. HDDs are calculated using outside air temperatures by subtracting the mean daily temperature from a base temperature (above which the building should need no further heating) and summing up the positive values over an entire year. The base temperature varies by jurisdiction but is usually set at around 65°F (18°C).

Heat Seaming: See Heat Welding.

Heat Sink: (During the application of sprayed polyurethane foam), a cold substrate that absorbs the heat of the chemical reaction, slowing down the process and the foaming action of the material.

Heat Transfer: The movement of thermal energy from one physical system to another through conduction (direct contact and the exchange of kinetic energy by particles), convection (the movement of a gas or liquid), or radiation (via the photons in electromagnetic waves).

Heat Welding: The process of joining together the overlapping edges of thermoplastic membrane sheets by heating them with hot air until they fuse. Also known as “heat seaming”.

Helm Roof: A steeply pitched pyramid-shaped roof with four gable ends that forms a spire.

Hem: In metalworking, the edge created by folding sheet metal back flush with itself; this is generally done for safety reasons or to improve dimensional stability.

Hex Shingles: Hexagonal shingles: Shingles whose visible areas are hexagonal after installation.

Hidden Nailing: See Blind Nailing.

Hiding Power: Covering power. Refers to coatings. The ability to hide the surface that a coating has been applied to.

Hip: The sloped edge at the intersection of two sloped roof sections.

Hip and Valley Roof: A roof that has both hips and valleys.

Hip Bevel: The angle between two sloped roof sections which are separated by a hip.

Hip Rafter: A rafter situated at the intersection of two roof sections on a hipped roof.

Hip Roof or Hipped Roof: A sloped roof with all (four) sides sloping down at the same angle, with hips where the different roof sections intersect. A hip roof has no gable ends.

Hip Shingles: Hip and ridge shingles. Shingles used to cover the edges formed by the intersection of two sloped roof sections.

Hip Tile: A specially-shaped tile used on the hip of a tiled roof.

Hoist: A device for raising or lowering people, materials, or equipment.

Holiday: An area where someone missed a spot during the application of paint or other coating material.

Honeycombing: Small voids in the surface of concrete due to the failure of the fine material in the mix to fill the spaces around the aggregate.

Horsefeathers: See feathering strip.

Hot: Roofers’ slang for hot roofing asphalt or coal tar pitch.

Hot-dip Galvanization: A galvanization process in which iron or steel is coated by being submerged in a bath of molten zinc.

Hot Stuff: Hot.

Humidity: The amount of moisture in the air, usually expressed as a percentage.

Hung GutterA trough suspended from the edge of the roof to collect and channel water flowing off the roof, usually to a downspout. The most common type of gutter.

HVAC: An acronym for Heating, Ventilation, and Air Conditioning.

Hydration: Mineral hydration of cement. The chemical reaction in which molecular compounds in Portland cement bond with water molecules to form a new crystalline structure, strengthening the material.

Hydrodynamic: Relating to the motion and forces of fluids.

Hydrodynamic Load: Structural load resulting from moving water that is in contact with a building.

Hydrostatic: Relating to the characteristics of fluids at rest.

Hydrostatic Load: Structural load resulting from water that is not moving or is moving very slowly

Hydrostatic Pressure: The pressure exerted by a static fluid due to its weight.

Hygrometer: An instrument used to measure the humidity of the surrounding air.

Hygroscopic: Refers to a material that tends to absorb moisture from the surrounding air.

HypalonDuPont’s trademark name for chlorosulfonated polyethylene (CSPE), which is used as a single-ply roofing membrane material. DuPont ceased production of Hypalon in 2010, although CSPE membrane is still manufactured by others.

I-Beam: A structural steel beam with a cross section resembling the letter I.

IBC: International Building Code. Model building code developed by the International Code Council and adopted, often with local amendments, by most jurisdictions in the United States.

IBHSInsurance Institute for Business & Home Safety

ICAAInsulation Contractors Association of America

ICBO: International Conference of Building Officials, former publisher of the Uniform Building Code. One of the three founding organizations of the International Code Council.

ICC: International Code Council. Publisher of the International Building Code.

Ice and Water Shield: A self-adhered rubberized asphalt underlayment typically applied on sloped roofs under mechanically-fastened roof coverings such as asphalt shingles, tile, or standing seam metal due to its ability to remain watertight when penetrated by fasteners such as roofing nails. “Grace Ice & Water Shield” was and is a trade name, but “Ice and Water Shield” has become genericized and is used to indicate any similar waterproofing membrane. 

Ice Dam: A build-up of ice at the overhanging eaves of a sloped roof where the roof’s surface transitions from warm to cold.  Due to the melting and re-freezing of snow and ice on the overhang, the ice accumulates, blocks drainage, and can force water back up under the shingles, causing leaks.

Ice Guard: Or snow guard. A device installed on a roof to prevent snow or ice from falling and hurting people, plants, or objects below.

Ignition Temperature: The minimum temperature to which a material must be heated for it to spontaneously ignite without an external ignition source such as a flame.

IIPLR: The Insurance Institute for Property Loss Reduction (now the Insurance Institute for Business & Home Safety).

Imbricate: Overlapping in a regular fashion, as with shingles or tiles.

Impact: A force or shock applied over a short period of time when two bodies collide.

Impact Load: A dynamic structural load on a building caused by an impact.

Impact Resistance: The resistance of a roofing material to a shock, such as from the impact of hail or foot traffic; the ability to resist damage from such a shock.

Impermeable: Not allowing water to pass through.

Impervious: Impermeable.

Imposed Load: All loads, except dead load, that are to be sustained by a structure.

Impregnate: To saturate and coat the fibers of (roofing felts, reinforcement mats, fabrics, etc.).

Inclination: The angle formed by a line or a surface by its intersection with the horizontal, the vertical, or another line or surface.

Incline: The steepness of a roof expressed as a ratio of vertical change to horizontal change such as rise/run or as a percentage (where 12/12 = 100%).

Indoor Air Quality (IAQ): a term that refers to the composition of the air inside and around buildings as it relates to the health and comfort of the occupants. ASHRAE Standard 62.1 defines acceptable IAQ as “Air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction.”

Infrared: Infrared radiation is electromagnetic radiation with longer wavelengths than those of visible light. Most thermal radiation emitted by objects near room temperature is infrared.

Infrared Thermography: Also thermal imaging. The use of an infrared camera to detect infrared radiation and produce images of that radiation. The amount of radiation given off by an object increases with temperature, so infrared thermography allows the detection of differences in temperature. Infrared cameras are typically used in non-destructive roof moisture surveys to identify wet areas of roof insulation, as wet insulation retains heat longer than dry insulation after the sun goes down.

Inorganic: Not composed of organic life nor the products of organic life (such as wood or cellulose); relating to compounds not containing hydrocarbon groups.

Insect Screen: A material, such as wire mesh, used to keep insects from entering a building through vents or other openings.

Inset Dormer: Also Recessed Dormer. A dormer which is partially set back from the surface of a sloped roof rather than projecting entirely beyond the sloped roof surface.

Insulating Concrete: Concrete with low thermal conductivity.

Insulation: (Thermal insulation.) Material used to help maintain a desired temperature by reducing the flow of heat.

Intake: An opening designed to allow the entry of air into an HVAC system.

Intake Ventilation: The elements of a ventilation system used to bring fresh air into a building. In a passive ventilation system, these are usually vents installed in the soffit or eaves of a building.

Integral Waterproofing: The improvement of the ability of concrete to resist water absorption by the addition of a admixture during the mixing of the concrete.

Interlaminar Adhesion: Refers to the adhesive bond between passes, or layers, of sprayed polyurethane foam.

Interlayment: A waterproofing material, such as roofing felt or sheet membrane, installed between adjacent courses of a steep-slope roof covering such as wood shakes to improve the roof’s waterproofing ability during periods of wind-driven rain or snow.

Interlocking Shingles: Individual shingles designed to mechanically attach to each other to improve the wind resistance of the roof covering. Also see T-Lock Shingles.

Intermediate Rafter: See Common Rafter.

Internal Pressure: Atmospheric pressure inside a building which is a function of external wind-speed, the ventilation system, and the number and location of openings in the building envelope.

International System of Units: Abbreviated “SI” for “Système International D’unités”. The metric system.

Intersecting Gable: See Cross Gable.

Interstitial Condensation: Also Concealed Condensation. Water vapor condensation within a building element, as within a roof assembly.

Intumescent: Describes a substance that swells up (increases in volume) as a result of heat exposure. Intumescent coatings are typically used in passive fire protection systems.

Inverted Roof Membrane Assembly (IRMA®): A type of protected membrane roof assembly in which Styrofoam® brand extruded polystyrene insulation is used. IRMA® and Styrofoam® are registered trademarks of the Dow Chemical Company.

IR: Abbreviation for “inside radius”.

IR: Abbreviation for “infrared”.

Irregular Pitch: Describes a roof with a slope that is not constant.

IRWC: Institute of Roofing and Waterproofing Consultants.

ISANTAInternational Staple, Nail, and Tool Association.

ISO: The International Organization for Standardization. “ISO” is not an acronym; rather, it’s a standardized short form of the name.

Iso: Also polyiso. Short for polyisocyanurate insulation.

Iso Board: Short for polyisocyanurate board insulation.

Isocyanate: Isocyanates are a family of highly reactive, low molecular weight chemicals. They are widely used in the manufacture of flexible and rigid foams, fibers, coatings such as paints and varnishes, and elastomers, and in the production of building insulation materials. They are a basic component of sprayed polyurethane foam.

Isolator: See Vibration Isolator.

Italian Roof: See “Hip Roof”.

Italian Tile: Mission tile.

Jack: See Roof Jack.

Jack Beam: A beam which supports a truss, beam, or other member, dispensing with the need for a supporting column.

Jack Rafter: A rafter which is shorter than the other rafters in the same assembly, typically found in hip or valley locations, where it butts into the hip or valley rafter.

Jack Truss: A truss which supports a beam, truss, or other member, dispensing with the need for a supporting column.

Joggle Cleat: A type of continuous metal cleat used to secure the ends of standing seam metal roof panels at the eave, valley, or other location where flat metal panels terminate longitudinally on a metal roof. The end of the metal panel is bent double and hooked over the joggle cleat.

Joint: A location where adjacent surfaces or components meet or are joined together, whether with fasteners, mortar, or in some other way.

Joint MovementThe difference between the minimum and maximum widths of a joint as dictated by building or component movement. This movement is frequently due to thermal expansion and contraction. 

Joint Residue: Accumulated detritus, such as deteriorated masonry or old sealant, that should be removed from a joint prior to the application of sealant.

Joint Sealant: A weatherproof sealant typically used to fill the joints between masonry building components such as tilt-wall sections or expansion joints.

Joint Tape: Tape used to seal joints between insulation boards.

Joist: Any of the parallel horizontal beams set from wall to wall to support the boards of a floor, ceiling, or roof of a building.

Joist Hanger: A metal bracket or strap used to secure the end of a joist.

Kerf: The width of a cut made by the blade of a saw.

Kesternich Test: Common name for various tests which use sulfur dioxide, a significant component of acid rain, in order to measure the resistance to corrosion of industrial products.

Kick-out: A section of a downspout assembly which typically uses an elbow piece to divert out-flowing water away from a building.

King-post: A vertical support post which extends from the apex to the tie-beam within a triangular roof-truss. (Also see Queen-post).

King-post Truss: A type of triangular roof truss which incorporates a vertical support member, at the apex of the truss, connecting the tie-beam and the rafters.

Knee Brace: A brace placed across the angle formed by two connected members, such as a joist and a rafter, in order to strengthen the assembly. Also called a corner brace.

Knee Cap: During metal roofing installation, in order for a metal roof panel to be bent to conform to a plane change in the substrate, the panel’s rib must be cut or notched at the location of the transition. A knee cap is the sheet metal cover piece that fits over the rib at the location of this cut.

Knee Rafter: A principal rafter which is bent at the lower end.

Knee Roof: see Curb Roof

Knee Wall: A wall which functions as a knee brace, extending from the rafters to the ceiling joists.

Knot: In membrane production, the presence of an imperfection that causes a surface irregularity.

Kraft Paper: see Building Paper.

K-ValueAlso called k-factor, or lambda value, λ. A measure of a material’s thermal conductivity regardless of the amount of the material. Thermal conductivity is defined by ASTM Standard C168 as “the time rate of steady state heat flow through a unit area of a homogeneous material induced by a unit temperature gradient in a direction perpendicular to that unit area”. K-value is calculated using watts per meter-kelvin (W/(m⋅K)).

Kynar: Kynar 500® is the Arkema, Inc. trade name for a polyvinylidene fluoride (PVDF) resin-based metal coating considered to be a premier coating for metal roofing materials.

Laitance: A layer of fine, powdery cement and aggregate particles on the surface of newly-cured concrete caused by the outward movement of water. The presence of laitance points to the use of too much water in the concrete mix. Laitance is a defect and prevents the proper adhesion of other materials, such as waterproofing, to the concrete.

Laminate: To create a product by bonding together two or more layers, or plies, of a material.

Laminated Shingles: Premium-grade asphalt-based strip shingles having more than one layer of tabs, giving them extra thickness and a textured appearance. Also called three-dimensional or architectural shingles.

Lap: 1.The part of a basic roofing material unit (shingle, felt, membrane sheet, roofing roll, etc.) that covers part of the preceding or adjacent course in an overlapping roofing application. 2. To cover part of one roofing course with another.

Lap Cement: An asphalt-based roofing adhesive used to adhere overlapping plies of asphalt roll roofing.

Lap Joint: A joint where the units of the material(s) overlap and are bonded or fastened together.  

Lap Seam: An area where two roofing material units that overlap are heat-seamed, adhered, or otherwise bonded together.

Latent Heat: Heat transferred during a phase change without a change in the substance’s temperature. Water vapor transfers heat to its surroundings as it condenses and absorbs heat from its surroundings as it vaporizes.

Latex: A stable emulsion of polymer microparticles in a water-based solution. After application, the latex coalesces into a film as the water evaporates. As in latex paint.

Lead:  A soft, heavy, malleable, bluish-white to dull graymetal that in sheet form is used as a roof flashing material. Lead is also a component of the solder typically used in copper roofing seams.

Leader: A leader pipe. Also called a conductor or downspout.

Leader Head: roof plumbing component used to direct water from a roof scupper or gutter to a downspout. Also known as a conductor head or a collector head.

Leader Pipe: A pipe for carrying water from a gutter, scupper, or other drainage system component from the roof to the ground or a sewer system. Also known as a downspout or conductor.

Leno Fabric: Atype of fabric used as scrim reinforcement in laminated roofing membranes. Leno fabric is marked by weft threads that are each wrapped by two warp threads to ensure stability by preventing the threads from moving relative to each other.

Life Cycle Cost Analysis (LCCA): An economic evaluation tool that assists in determining the most cost-effective option among different alternatives in the purchasing, owning, operating, maintaining, and disposing of an asset, when each is equally appropriate on technical grounds. For a roof, in addition to the initial installation cost, LCCA accounts for all owner costs including warranty fees, scheduled maintenance or cleaning costs, reductions or increases in building heating and cooling costs associated with the roof, expected repair costs, and removal cost.  

Lift: A device used for raising or lowering people, equipment, or materials.

Lift: The thickness of a layer of spray polyurethane foam after a pass.

Lifting: The swelling or separation from the substrate of a dried layer of coating as the result of the application of a subsequent coat.

Light Reflectance Value (LRV): On a scale of 0% to 100%, a measure of the visible and usable light reflected from a surface when illuminated by a light source. The higher the LRV, the more reflective a surface is, with bright white being around 85%, and dark black being around 5%.

Lightning Protection System: A system of strike termination devices, conductors, grounding electrodes, interconnecting conductors, surge protection devices, and connectors designed to protect structures from fire or mechanical damage due to lightning strikes

Lightning Rod: A metal rod that serves as a strike termination device in a lightning protection system.

Lightweight Concrete: Concrete that is of a significantly lower density than normal concrete due to the addition of an air-entraining agent or lightweight aggregate such as vermiculite, perlite, gypsum, or cellulosic fibers. Its equilibrium density tend to be between 70 and 120 lb/ft3 (1120 and 1920 kg/m3). Used as a poured deck fill on roof decks.

Lightweight Insulating Concrete (LWIC): A roof deck systemin which lightweight concrete is used in conjunction with a structural deck and, typically, expanded polystyrene insulation boards to increase the roof assembly R-value and create a contoured, monolithic substrate for the roof system.

Lintel: A horizontal structural member over a window or door which carries the weight of the wall above it.

Live Loads: Also called imposed loads. Temporary loads on a roof such as people, equipment, stored materials, or snow which the structure must be designed to support as required by code.

Load Deflection: See Deflection.

Loads: Or structural loads. Forces that act on structures or their members.

Loose-Laid: Of single-ply roof membranes and insulation boards. Not adhered or mechanically attached to the substrate.

Loose-Laid Roof Membrane: A roofing membrane (such as an EPDM membrane) that is attached to the substrate only at the perimeter and at penetrations, and is typically held in place by stone ballast or pavers.

Louver: A opening with angled, horizontal slats designed to admit light or air but not precipitation or direct sunlight.

Low Balling: Deliberately bidding low on a project, often with the intention of increasing the project’s total billable amount later through cost overruns and change orders.

Low Slope Application: Method of installing asphalt shingles on roofs with slopes that are between 2/12 and 4/12.

Low Slope Roof: A roof with a maximum slope of less than 3 inches vertical rise for every 12 inches of horizontal run. A roof with a slope of less than 14 degrees.

O.C.: On Center

Off-Ratio Foam: Polyurethane foam which has been improperly mixed during application.

Oil Canning: Slight physical distortions of flat metal panels that appear as ripples in the metal and detract from a desirable flat and uniform appearance of the panels.

Olefin: A relatively stable, unsaturated chemical compound, such as ethylene or propylene, containing at least one carbon-to-carbon double bond. Widely used as a basic material in the petrochemical industry. See TPO.

On Center: Refers to measurements being made from the center of the members (studs, rafters, joists, etc.).

Open Time: The time after an adhesive has been applied to a substrate during which a proper bond can be made.

Open Valley: A roof valley construction technique in which the shingles on each side are cut back, so that the shingles do not cover the valley, and the valley flashing material is exposed. Also see “Woven Valley”.

Open Web Steel Joist:  A lightweight steel truss with a triangulated web and parallel chords, typically used to support floors and roof decks. Also called a “bar joist”.

Orange Peel Surface Texture: Typically used in reference to spray polyurethane foam. A surface texture similar to that of the outside of an orange, acceptable as a surface to which a protective coating may be applied.

Organic: 1. Formed from material that was once part of a living organism. 2. Containing hydrocarbons.

Organic Felt: A substrate, produced in sheets, made from cellulose fibers and used in the production of roll roofing, asphalt shingles, base sheets, and reinforcement plies in built-up roofs.

Organic Shingle: An asphalt shingle manufactured with organic felt.

Oriented Strand BoardEngineered wood panels produced by compressing layers of wood strands and adhesive, with the wood strands of each layer being at right angles to those of the next layer. It is commonly used as an alternative to plywood in structural sheathing applications. Also called OSB.

Original Construction: The parts of a building that date from the time the building was first constructed.

ORNL: Oak Ridge National Laboratory

OSB: Oriented Strand Board

OSHA: (U.S.) Occupational Safety and Health Administration

Overhang: A part of a building that protrudes beyond the exterior walls and protects the area below it. When the overhang is an extension of the roof, it is referred to as the “eaves”.

Overlay: The installation of new material over existing material. See Recover.

Overnight Tie-in: A temporary waterproofing application at the edge of a section of newly-installed roofing to prevent water from infiltrating the area while the installers are away. 

Overspray: The unintended loss or misapplication of spray-applied material during application.

Ozone:  (O3). A highly reactive gaseous molecule present in the atmosphere and having a corrosive effect on virtually all roofing material.

Ozone Resistance: The ability of a material to remain unreactive in the presence of ozone.

Qualitative Test: A test that determines whether or not a specific substance is present in the sample.

Quality Assurance: (Abbreviated QA.) Observation and documentation of construction activity with the goal of ensuring that the outcome of the project is a product that is in accordance with industry standards, the project specifications and other contract documents, and any other relevant standards.

Quantitative Test: A test that determines the amount of a specific substance present in the sample.

Quarry Tile: Unglazed tile produced by extrusion from natural clay or shales.

Queen-post: Either of two vertical support posts which are set at an equal distance from the apex of the roof within a triangular roof truss. (Also see King-post).

Queen-post Roof: A roof supported by queen-posts.

Queen-post Truss: A type of triangular roof truss which incorporates two vertical support members, on each side of the apex of the truss, connecting the tie-beam and the rafters.

Quick-setting cement: A type of fast-drying asphalt-based or asphalt-compatible cement used to adhere the butt edge of shingles or roll roofing to the course below.

Quonset Hut: A prefabricated building, semi-circular in cross-section, typically consisting of a corrugated metal roof, which also functions as the walls of the structure, with vertical closure pieces at either end.

Quotation: (Or Quote.) A vague term in the construction industry that may or may not be the same thing as an estimate or a proposal. It generally indicates a good faith price for work to be performed by a contractor, or for material to be provided by a supplier.

QTR: Quarry Tile Roof

QUV: A laboratory testing technique which simulates weathering effects on a material at accelerated rates.

UBC: Uniform Building Code.

UL: Underwriters Laboratories Inc. (which see).

UL Label: See UL Mark.

UL Mark: (From the UL website): The UL Mark on a product means that UL has tested and evaluated representative samples of that product and determined that they meet UL requirements. On roofing materials, the UL mark is typically found on a label that has been affixed to the material’s packaging.

Ultraviolet Light (UV): A range of electromagnetic radiation with a frequency higher than visible light, but lower than X-rays. UV rays contribute to the breakdown of chemical bonds, and thus can cause the deterioration of many types of roofing materials. Asphalt is at particular risk of UV degradation due to the length and instability of the molecular chains comprising the material. The prevention of UV degradation is the primary reason for the protective surfacing applied to bitumen-based roofing materials.

Undereave: See Soffit.

Underlayment: A sheet material applied directly over the roof deck before the installation of the roof system. Underlayments function in various roles, including as air barriers, as vapor retarders, as protection against ice dams, and as a secondary water barrier.   

Underwriters Laboratories (UL): An OSHA-approved independent product safety certification organization. It operates laboratories devoted to the testing, evaluation, and certification of a wide range of commercial products, assemblies, systems, and materials.

Uplift: In the context of roofing, wind uplift (which see).

Urban Heat Island Effect: From the EPA website: “The urban heat island effect is a measurable increase in ambient urban air temperatures resulting primarily from the replacement of vegetation with buildings, roads, and other heat-absorbing infrastructure. The heat island effect can result in significant temperature differences between rural and urban areas.”

Urethane: See Polyurethane.

U-Value: A term used in building science to refer to the overall heat transfer coefficient of a building component, i.e., a description of how well the component conducts heat.

UV Degradation:  Damage done to a material at the molecular level by ultraviolet light.

Valley: A trough or gutter formed by the angle of two sloped roof sections intersecting at less than 180 degrees (when viewed from outside of the building). The opposite of a hip. Valleys are channels for water run-off and are usually subjected to greater hydrodynamic forces than other sloped roof areas.

Valley Flashing: The (typically) sheet metal material used to line a roof valley.

Valley Gutter: A specially-formed roof component installed in a roof valley to carry water down the roof while withstanding the greater hydrodynamic forces a valley normally experiences.

Valley Jack: A rafter that is attached to the ridge at one end and a valley rafter at the other. Shorter than a common rafter.

Valley Rafter: The rafter that follows and supports the line of a roof valley, connecting the ridge to the wall plate where two sloped roof sections intersect.

Valley Roof: A roof that has at least one valley.

Vane: See Weather Vane.

Vapor Barrier:  Vapor Retarder. A material, such as a waterproof coating or a sheet membrane, installed to prevent or reduce the movement of water vapor into a building component, such as a roof assembly, in order to prevent interstitial condensation.

Vapor Flow: The movement of water vapor from areas of high water content to areas of low water content as a function of temperature and relative humidity.

Vapor Migration: See Vapor Flow.

Vapor Pressure: Or equilibrium vapor pressure. The pressure at which a liquid and its vapor are in equilibrium at a specific temperature; the pressure of the vapor resulting from evaporation of a liquid in contact with the liquid in an enclosed area.

Vapor Retarder: See Vapor Barrier.

Variance: Authorization from the responsible authority permitting construction that deviates from the rules set out in the governing code.

Veneer: 1. Masonry Veneer: A non-structural facing layer of (usually) brick. 2. Wood Veneer: A thin layer of wood glued to a substrate such as particle board to give the appearance of solid wood. One of the thin layers of wood which are glued together to create plywood, each with the grain at a right angle to the next to improve structural strength and stability.  

Veneer Tie: A strip of metal used to hold a masonry veneer to the wall that it covers.

Vent: An opening or device designed to transfer air, heat, water vapor, or exhaust gases from an enclosed structure into the atmosphere. Also see Intake Ventilation.

Vent Cap: A piece that protects the open end of a vent stack from precipitation or debris while still permitting air flow.

Ventilation: The process of intentionally allowing or forcing air to enter and exit an enclosed space.

Ventilator: A device that forces the intake and expulsion of air in an enclosed space.

Vent Pipe: A pipe that serves as a vent.

Vent Sleeve: A pre-formed flashing unit designed to fit around a vent pipe.

Vent Stack: A plumbing vent that typically penetrates the roof.

Verge: The projecting edge of the roofing material (such as tiles) above a gable.

Vergeboard: See Bargeboard.

Verge Trim: Roof component which protects and secures the verge of a roof.

Verge of Popcorn Texture: The roughest surface texture of a spray polyurethane foam roof that is considered acceptable for receiving the protective waterproof coating. Extra coating material is required for proper coverage and this texture is therefore considered undesirable.

Vermiculite: A hydrous phyllosilicate mineral which undergoes significant expansion when heated. Vermiculite is used as an aggregate in some lightweight insulating concretes and as a loose-fill insulation.

Vibration Isolator: A support for rooftop equipment designed to reduce the amount of vibration transmitted from the equipment to the building structure.

Viscosity: The measure of a fluid’s resistance to flow.

Viscous: Highly resistant to flow.

Visor Roof: See Pent Roof.

Visual Inspection: Inspection by sight alone, without the use of any testing devices.

Vitrified Brick: Glazed brick that is impervious to water penetration.

VOC: Volatile Organic Compounds.

Void: An empty space or break in continuity. In a built-up roof, an area between two felts that has no bitumen.

Volatile: Describing something which easily vaporizes or evaporates quickly.

Volatile Organic Compounds: Organic chemicals having a high vapor pressure at room temperature, causing them to easily transform from liquid or solid into vapor at an ordinary temperature and pressure.

Vulcanization: A chemical process that improves the strength and resiliency of natural or synthetic rubber by combining the material with sulfur or similar additives under heat and pressure.

Wagon Roof: See Barrel Roof.

Walkway Pads: Durable pieces of material that can resist physical damage that are installed on top of the roof covering to form walkways in high foot traffic areas on a roof, such as from an access point (like a hatch) to items (like HVAC units) which require regular maintenance.

Wall Dormer: A dormer whose face is an unbroken continuation of the face of the wall below.

Wall Plate: A horizontal structural member at the top of a wall that supports the members, such as the rafters, that support the roof.

Warp: In weaving, the lengthwise yarns that are held in place on a frame while the weft yarns are inserted through them crosswise during the weaving process.

Warranty:  A written, legally-binding guarantee or promise issued by a manufacturer or roofing contractor to the end consumer of roofing materials or services that the materials or installed system will perform as expected under the stated conditions. A warranty is generally an element of the roofing contract, expires after a stated period of time, and requires the roofing manufacturer or roofing contractor to repair or replace, at no charge, a roof system or the part of a roof system which does not perform as promised.  

Wash: The slope of the upper surface of a building element such as wall coping or a window sill designed to shed water away from the building.

Water Absorption: A physical property of a material, indicating the amount of water that will be absorbed by the material when immersed in water. Typically expressed as the weight increase of the material, as a percentage of its dry weight, after the material has been immersed in water for a specified time at a given temperature.

Water Cure: A technique for controlling the rate of cure of a material, such as concrete, by applying water in the form of a fine mist to the surface to regulate moisture evaporation from the material.

Water Cut-off: See Overnight Tie-in.

Water Cut-off Mastic: A mastic intended to be used as a sealing agent between various membranes and substrates and typically applied at membrane terminations using a compression-type seal.

Waterproof: Impervious to water.

Waterproofing: 1. The process of making a surface or structure impervious or resistant to water. 2. The material applied during this process.

Water Resistant: Able to withstand light or temporary exposure to water but not impervious to water.

Water Stop: Material installed over a joint in a concrete structure to prevent water from entering the joint.

Water Testing: A method of identifying leaks in the building envelope through the controlled application of water to the surface of a building component. Also see Flood Testing. 

Water Trough: The part of a roof valley that channels the water running down it.

Water Vapor: The gaseous phase of water.

Water Vapor Transmission Rate: A measure of the passage of water vapor through a material under specific conditions of temperature and humidity.

WBT: Wet Bulb Temperature.

Wear Course: Or wearing course. The top layer of a surfacing application designed to withstand foot or vehicle traffic.

Weather: The exposed part of an installed wood shingle.

Weather Block: Mortar used to fill openings in tile roofs to prevent infiltration by water or debris.

Weathering: The degradation in quality and appearance which is caused by normal exposure to the atmosphere, sunlight, and living things.

Web: The interior members of a truss.

Weep Holes: Small holes designed to allow the drainage of water that has entered a building component such as a cavity wall or a skylight frame.

Weft: See Warp.

Weld: To join metal or thermoplastic components together by heat fusion.

Wet Bulb Temperature: The temperature of the air as measured by a thermometer with a bulb covered by a damp wick.

Wet Film Thickness: The thickness of a coating after it is applied but before it cures.

Wicking: The movement of a liquid by capillary action.

Wind Clip: A device that secures the butt end of an individual piece of a steep-slope roof covering such as tile or slate to prevent wind uplift damage.

Wind Load: A type of structural load. The force exerted on a structure by wind.

Wind Scour: The erosion of the protective surfacing on a roof due to the action of the wind. Usually occurs in the corner of a roof, where wind vortices form.

Wind Uplift: The force that acts on a roof assembly due to the drop in air pressure above the surface of the roof when wind blowing across the roof is deflected upward by the side of the building or other obstruction. Air pressure below the roof tends to increase at the same time due to air infiltration into the building through openings such as doors, windows, or cracks, creating a pressure differential that forces the roof membrane upwards.

Windward: Facing the prevailing wind.

Wire Tie System: An attachment system for heavy steep-slope roof covering units such as slates or tiles that uses wire in addition to nails or screws.

Withe: A continuous vertical section of a masonry wall, one unit wide.

Woven Valley: A method of installing asphalt shingles in a roof valley in which the shingles from each side of the valley extend across the valley and are woven together by having the shingles from one side overlap the shingles from the other side in alternating courses. In a woven valley, the valley flashing is not exposed and the shingles form the surface of the water trough.

X-brace: (Or cross brace). Braces which cross each other in the form of the letter X.

Yellowing: The process whereby a white or clear coating becomes yellow as a result of aging.

Yelm: A bundle of combed straw or reeds used as thatch.

Yield: The amount of finished product produced from a known quantity of ingredients.

Yield Point: The level of stress at which a material undergoes a non-reversible change in shape, or permanent deformation.

Yield Strength: The amount of stress a material can undergo before achieving a non-reversible change of shape, or permanent deformation. Prior to the yield point, stress may result in elastic behavior, where the material will return to its previous shape after the stress is removed.

Zax: A multi-purpose hand tool used by slaters to shape and punch holes in roofing slates.

Z Bar: A type of metal counterflashing formed in the shape of a “Z” and typically used on stucco or wood-clad walls.

Zinc: A bluish-white, lustrous metallic element that is brittle at room temperature but malleable when heated. It is generally not subject to corrosion. It is used to form a wide variety of alloys including brass, bronze, various solders, and nickel silver; it is used to galvanize iron and steel, and for electric fuses, anodes, and meter cases, and in roofing, gutters, flashings, edge metals and also for various household objects. Atomic number 30; atomic weight 65.37; melting point 419.4 °C; boiling point 907 °C; specific gravity 7.133 (25 °C); valence 2.

Zinc Oxide: A white powder, ZnO, which is insoluble in water and used as an additive in a number of industrial applications. Paints containing zinc oxide are commonly used as anti-corrosive coatings on metal surfaces.

Zoning: The regulation by a municipality of the use of land and buildings in order to direct, control, promote, or restrict development.