Here you can find a comprehensive glossary of roofing terms. Feel free to contact us if you have any questions.
Adhere: The clinging of one surface to another; either molecularly or otherwise.
Aggregate: A surfacing or ballast for a roof system. Aggregate can be rock, stone, crushed stone or slag, water-worn gravel, crushed lava rock or marble chips.
Alligatoring: The cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks that resemble an alligator’s hide.
Application Rate: The rate at which a material is applied per unit area.
Apron Flashing: A flashing located at the low end of a curb or penetration.
Architectural Shingle: Shingle that provides a dimensional appearance. See also Dimensional 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.
Asphalt: A substance left as a residue after evaporating or otherwise processing crude oil or petroleum. Asphalt can be refined to conform to various roofing grade specifications.
Asphalt Felt: An asphalt-saturated and/or an asphalt-coated felt membrane. See also Felt.
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.
Back-Nailing: The method of fastening the back or upper side of a ply of roofing felt or other component in a roof system so that the fasteners are covered by the following ply.
Ballast: A material installed over the top of a roof membrane to help hold it in place. Ballasts are loose laid and can consist of aggregate, or concrete pavers.
Base Flashing (membrane base flashing): Plies of roof membrane material used to seal a roof at the vertical plane intersections, such as at a roof-wall and roof-curb junctures. See also Flashing.
Base Ply: The primary ply of roofing material in a roof system.
Base Sheet: An asphalt-impregnated, or coated felt used as the first ply in some built-up and modified bitumen roof systems.
Bitumen: Any of various flammable mixtures of hydrocarbons and other substances, occurring naturally or obtained by distillation from coal or petroleum, that are a component of asphalt and tar and are used for surfacing roads and for waterproofing.
Bitumen-Stop: A continuous seal for preventing bitumen from leaking down into or off a building. Is constructed by extending the base sheet or other non-porous ply of felt beyond the edge of the field plies. It is then turned back onto the top of the system and adhered.
Blind-Nailing: The use of nails so that they are not exposed to the weather in the finished roofing system. See Back-Nailing
Blocking: Pieces of wood built into a roof assembly used to stiffen the deck around an opening, support a curb, or for use as a nailer for attachment of membranes or flashing.
Brooming: Embedding a ply of roofing material into hot bitumen or adhesive by using a broom, squeegee, or other piece of equipment to eliminate voids and help ensure adhesion.
Built-Up Roof Membrane: A roof membrane consisting of layers of bitumen, which serves as the waterproofing component, with plies of reinforcement fabric installed between each layer. The reinforcement material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate, emulsion or a granule-surfaced cap sheet.
BUR: An acronym for Built-Up Roof. See Built-Up Roof
Cant: (1) Short for Cant Strip; (2) The act of installing foam at a right angle adjunct.
Cant Strip: A triangular-shaped strip of material used to ease the transition from a horizontal plane to a vertical plane. Cant strips can be made of wood, wood fiber, perlite, or other materials.
Cap Flashing: A material used to cover the top edge of base flashings or other flashings. See also Coping.
Cap Sheet: A granule-surfaced membrane often used as the top ply of BUR or modified roof systems.
Caulking: The act of sealing a joint or of material.
Channel Flashing: Flashing with a built-in channel for runoff; used where roof planes intersect other vertical planes.
Closed-Cut Valley: A method of valley application in which shingles from one side of the valley extend across the valley while shingles from the other side are installed over the top of those and then trimmed back approximately 2 inches from the valley centerline.
Coal Tar Pitch: A type of coal tar used in dead-level or low-slope built-up roofs. It is not for use in roofs exceeding ¼" in 12" (2%) slope.
Coal Tar Roof Cement: A trowelable mixture of processed coal tar base, solvents, mineral fillers and/or fibers.
Coated Base Sheet: An asphalt-saturated base sheet membrane later coated with harder, more viscous asphalt, thereby increasing its impermeability to moisture.
Coated Felt: An asphalt-saturated ply sheet that has also been coated on both sides with harder, more viscous asphalt.
Composition Shingle: A type of shingle used in steep-slope roofing and generally comprised of weathering-grade asphalt, a fiber glass reinforcing mat, an adhesive strip, and mineral granules.
Coping: The piece of material used to cover the top of a wall and protect it from the elements. It can be constructed from metal, masonry, or stone.
Curb: (1) A raised member used to support skylights, HVAC units, exhaust fans, hatches or other pieces of mechanical equipment above the level of the roof surface, should be a minimum of eight inches (8") in height; (2) A raised roof perimeter that is relatively low in height.
Cut-off: A detail designed to seal and prevent lateral water movement in an insulation system, and used to separate different sections of a roofing system.
Cutout: The open area between shingle tabs. Also known as a "throat".
Dampproofing: Treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.
Dead Level: Refers to a roof with no slope or pitch.
Dead Loads: Permanent, non-moving loads on a roof resulting from the weight of a building’s components, equipment, and the roof system
Deck: The structural component of the roof of a building which provides the substrate to which the roofing system is applied.
Decking: See Deck.
Degradation: A decline in the appearance, structure, or properties, of a material or substance.
Diffusion: The movement of a substance such as water vapor from regions of high concentration to regions of lower concentration
Dimensional Shingle: A shingle that is textured, or laminated to produce a three-dimensional effect. Also known as Laminated and Architectural Shingles. Please be aware that there are also shingles being produced that can be classified as Dimensional but not as Laminated. These shingles are comprised of a single piece of material rather than two different materials laminated together.
Dimensional Stability: The ability of a material to retain its current properties and to resist a change in size resulting from exposure to temperature changes and moisture.
Dome: A roof with a partial-spherical shape.
Double Coverage: Installing roofing so that there is twice the materials used resulting in a double layer of roofing.
Double Graveling: Installing one layer of gravel in a flood coat of hot bitumen, removing the excess gravel and then installing a second layer of gravel in another flood coat of hot bitumen.
Downspout: A conduit for carrying water from a gutter, scupper, drop outlet or other drainage unit from roof to ground level. Also known as a Leader Pipe.
Drain: A device used to carry water off of a roof.
Drip Edge: A steel flashing bent at a 90º angle that is placed along the outer perimeter of steep sloped buildings; used to help direct runoff water away from the building. Drip Edge resembles nosing except that it has an outwardly-angled bottom edge (preferably hemmed).
Dry-In: (1) The process of installing the underlayment in steep slope roofing; (2) Making a low-slope roof watertight. Does not always mean getting all of the required plies installed.
Dry Rot: Wood rot caused by certain fungi. Dry rot can result from condensation build-up, roof leaks that go untended, or from other problems. Dry rot will not remain localized. It can spread and damage any lumber touching the affected area.
Eave: A roof edge that extends out past the exterior wall line.
Eaves-Trough: Another name for Gutter.
Edge Stripping: Roofing material used to seal perimeter edge metal and the roof itself.
Embedment: In roofing, to uniformly press one material into another, such as aggregate into bitumen, roofing felt into bitumen, or granules into a coating.
Envelope: A continuous seal for preventing bitumen from leaking down into or off a building. Is constructed by extending the base sheet or other non-porous ply of felt beyond the edge of the field plies. It is then turned back onto the top of the system and adhered. See also Bitumen-Stop.
EPDM: Ethylene Propylene Diene Monomer.
Epichlorohydrin (ECH): A synthetic rubber material similar to EPDM with a stronger resistance to animal fats and oils than EPDM.
Epoxy: A type of synthetic, thermosetting resins that produce tough, hard, chemical-resistant coatings and adhesives.
Eyebrow: A small, shed roof protruding from the main roof or located on the side of a building below the level of the main roof.
Fascia: Vertical roof trim located along the perimeter of a building, usually below the roof level. Its use can be either decorative or for waterproofing.
Fasteners: Devices used to secure roof system components.
Felt: A roofing sheet made of interwoven fibers. The fibers can be wood or vegetable for Organic Felts, glass fibers for fiberglass felts, polyester, or asbestos.
Field Seam: A non-factory material seam made by joining overlapping seams together with adhesives, heat welders, or other means.
Flame Retardant: A substance used to impede a material’s tendency to burn or ignite.
Flashing: Components used to seal the roof system at areas where the roof covering is interrupted or terminated. For example, pipes, curbs, walls, etc. all have special components that, when correctly installed, will help prevent moisture entry into the roof system or building.
Gable: A triangular-shaped portion of the endwall of a building directly under the sloping roof and above the Eave line.
Galvanize: To coat with zinc.
Galvanized Steel: Steel that is coated with zinc to aid in corrosion resistance. Galvanized steel for use in roofing should be Hot-Dipped Galvanized with a G-90 coating.
Granules: A small aggregate, naturally or synthetically colored, used to surface cap sheets, shingles, and other granule-surfaced roof coverings.
Gravel Stop: A flanged, sheet metal edge flashing with an upward projection installed along the perimeter of a roof to stop the flow of bitumen over the edge.
Gutter: A channel (usually sheet metal) installed along the downslope perimeter of a roof to convey runoff water from the roof to the drain leaders or downspouts.
Hand-Tabbing: Applying spots of adhesive to shingle tabs.
Hatch: A unit used to provide access to a roof from the interior of a building.
Headlap: The distance that the topmost ply of roofing felt overlaps the undermost ply or course.
Hip: The angle formed by the intersection of two sloping roof planes.
Hoist: A mechanical lifting device. A hoist can be hand or electrically operated.
HVAC: Acronym for Heating, Ventilating, and Air Conditioning.
Insulation: Material used to help maintain a certain temperature in a building by reducing the flow of heat to and from that building. See also Thermal Insulation.
Intake Ventilation: The part of a ventilation system used to draw fresh air in. Usually vents installed in the soffit or along the eaves of a building.
Interlayment: A waterproof material usually installed between adjacent rows of wood shakes to help with the roof’s waterproofing characteristics.
Interlocking Shingles: Shingles that lock together to provide wind resistance.
Inverted Roof Membrane Assembly (IRMA®): A variation of the "Protected Membrane Roof Assembly" in which Styrofoam® brand insulation is used. IRMA® and Styrofoam® are registered trademarks of the Dow Chemical Company.
Isocyanate: A highly reactive organic chemical containing one or more Isocyanate groups. A basic component in Sprayed Polyurethane Foam systems and some polyurethane coating systems.
Joint Tape: Tape used to seal joints between insulation boards.
Knee Cap: Sheet metal trim that fits over a panel rib after it has been cut and bent.
Laminated Shingles: See Dimensional Shingles or Architectural Shingles.
Leader Head: A component used to direct water from a through-wall scupper to a downspout. Also known as a Collector Head.
Leader Pipe: A conduit for carrying water from a gutter, scupper, drop outlet or other drainage unit from roof to ground level. Also known as Downspout.
Loose-Laid Roof Membranes: Roofing material attached only at the perimeter and at penetrations and held in place by ballast, pavers, or other materials.
Mansard: (1) A steep-sloped roof located at the perimeter of a building and usually used for decorative purposes. (2) The upper story formed by the lower slope of a mansard roof.
Mansard Roof: A steeper roof that terminates into a lower sloped roof at its high point.
Masonry: Refers to bricks, concrete, or concrete blocks.
Mastic: See Asphalt Roof Cement.
Mechanical Fasteners: Devices such as screws, plates, battens, nails, or other materials that are used to secure roofing materials.
Membrane: The portion of the roofing system that serves as the waterproofing material. Can be composed of one material or several materials laminated together.
Metal Flashing: Roof components made from sheet metal that are used to terminate the roofing membrane or material along roof edges. Metal flashings are also used in the field of the roof around penetrations.
Meter: Metric unit of length measurement equal to 39.37 inches.
Millimeter: Metric unit of measure equal to one thousandth (0.001) of a meter, or 0.03937 inches.
Mineral Granules: See Granules.
Mineral-Surfaced Roofing: Roofing materials with a top surface consisting of mineral granules.
Moisture Relief Vent: A vent installed through the roofing membrane to relieve moisture vapor pressure that has been trapped within the roofing system.
Moisture Scan: A survey of a roof specifically to detect the amount of moisture present in the roof system. Devices used in moisture surveys can be capacitance meters, infrared cameras, and nuclear scanners. Infrared scans can be done from the air or on the surface of the roof. Capacitance and nuclear scans are done on the roof surface. It is argued that the most accurate scans are done from the surface of the roof with the most accurate of these being nuclear scans.
Mole Run: A term used to describe a ridge in a roof membrane that is not the result of improper deck or insulation joints.
Monomer: A simple molecule that can combine with other to form a polymer.
Mop-and-Flop: A roofers’ term where the back side of a roofing material is mopped, then the piece is turned over and set in place.
Nailing Pattern: Refers to a specific method or pattern at which nails are applied. For instance, a nailing pattern for base sheets on plywood roof decks can be "Nine and Eighteen". This means one row of nails on the outside edge of the sheet set at nine inches (9") on center, and two rows in the center of the sheet, each set at eighteen inches (18") on center.
Nesting: To overlay existing shingles with new shingles and butt the top edge of the new shingle up against the bottom edge of the existing shingles.
Night Seal: To temporarily seal the edge of a roof membrane in order to protect it from moisture entry. A.K.A. Night Tie-Off and Water Cut-Off.
Ninety-Pound: Granule-surfaced or fiber glass or organic felt roll roofing that has a mass of approximately 90 pounds per 100 square feet.
No-Cutout Shingle: A shingle made of one solid strip of material.
Non-Breathing Membrane: A membrane that does not permit water vapor or air to permeate it.
Non-Flammable: Material with no measurable flash point.
Nonwoven: Random arrangement of the reinforcement fibers of a scrim sheet or mat.
Open Valley: A valley where both sides of the roof are trimmed back from the centerline to expose the valley flashing material beneath.
Overlay: See Re-Cover.
Overspray: The loss of spray particles (from coatings, SPF, etc.) in the air.
Pan: (1) The concave piece of "Pan and Cover" tile whose rounded surface touches the top side of the roof substrate. (2) The flat part of a roofing panel located between the ribs.
Pan Flashing: A sheet metal flashing that covers an equipment platform and is designed to counter flash the base flashings surrounding the platform.
Pass: The term used to describe the application of one layer of Spray Polyurethane Foam (SPF). The speed of a pass will determine foam thickness.
Pass Line: The distinct line formed between two passes of SPF. This line is the top skin of the bottom pass of the SPF.
Penetration: Any object that pierces the surface of the roof.
Permeability: The rate of flow of a liquid or gas through a porous material.
Phasing: Installing roof system components in separate time intervals. For instance, installing a base sheet, and then two plies of roofing one day, and coming back and installing the remaining two plies one or more days later. It is generally not considered Phasing if the surfacing is applied at a later date.
Pipe Boot: A prefabricated flashing piece used to flash around circular pipe penetrations. Also known as a Roof Jack.
Pitch: Term used to describe Roof Slope and also short for Coal Tar Pitch.
Pitch Pocket (A.K.A. Pitch Pan): A flanged piece of flashing material placed around irregularly shaped roof penetrations and filled with grout and a pourable sealer to seal around the penetration in order to seal it against moisture entry. Pitch pockets are a good source of leaks and should be avoided if possible.
Ply: A layer of felt or other reinforcement material in a roof system.
Polymer: Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule.
Polymer Modified Bitumen: See Modified Bitumen.
Ponding: The accumulation of water at low-lying areas on a roof.
Pop Rivet: A small metal pin having a head on one end, inserted through aligned holes in pieces of light gauge metal to be joined and then the head is expanded to join the metal.
Pourable Sealer: A type of sealant that is initially in liquid form commonly used in conjunction with pitch pans to form a water-tight barrier around penetrations that are difficult to flash.
Primer: A material that is applied to a surface in order to increase that surface’s ability to adhere to or work in conjunction with a subsequently applied material.
Protected Membrane Roof (PMR): A roof assembly in which the insulation and ballast are placed on top of the membrane component. Commonly referred to as an "inverted roof assembly."
Puncture Resistance: The ability of a material to withstand being pierced by a sharp object.
PVC: Polyvinyl Chloride.
Racking: The method of installing asphalt shingles where the shingles are installed straight up to the ridge rather than horizontally. If this method is used with 3-tab shingles, the throats of every other course will line up.
Rafter: The structural member extending from the downslope perimeter of a roof to the ridge or hip and is designed to support the roof deck and roof system components.
Re-Cover (Overlay): The installation of a new roof system over an existing system without removing an existing system.
Reinforced Membrane: A roofing membrane that has been strengthened by adding polyester scrims or mats, glass fibers or other material.
Relative Humidity: The amount of water vapor in the air compared to the amount of water vapor that the air can hold at a given temperature. For example, if the relative humidity is 50 percent, then the amount of water vapor in the air is half of what the air could actually hold at that temperature.
Reroofing: The procedure of installing a new roof system.
Ridge: The line where two planes of roof intersect, forming the highest point on the roof that runs the entire length of the roof.
Ridge Cap: Material applied over the ridge or hip of a roof.
Ridge Course: The final course of roofing applied that covers the area where two or more roof planes intersect.
Ridge Vent: An exhaust venting device located at the ridge of a roof that works in conjunction with a starter or under eave soffit vent and is used to ventilate attics. Ridge vents and their cooperative starter or soffit vents should be installed at a 1:1 ratio in order to function properly.
Roof Assembly: A term used to describe all of the roof components including structural roof deck.
Roof Cement: See Asphalt Roof Cement and Coal Tar Roof Cement.
Roof Covering: The outermost reinforced layer of the roof assembly. In BUR it’s the multiple-ply membrane, in Thermoplastic roof systems it’s the thermoplastic sheet, etc.
Roof Curb: A frame used to structurally mount rooftop equipment such as HVAC units, exhaust fans, skylight, etc.; may be pre-constructed or constructed on site.
Roof Overhang: That portion of the roof that extends beyond the exterior wall line of the building.
Roof Seamer: (1) A mechanical device used to crimp metal roof panels and make the seams watertight. (2) A machine used to weld membrane laps of PVC (Thermoplastic) roofing material.
Roof Slope: The angle made by the roof surface plane with the horizontal plane and expressed as the amount of vertical rise for every twelve inch (12") horizontal run. For instance, a roof that rises four inches (4") for every twelve inch (12") horizontal run, is expressed as having a "four in twelve" slope; often written as "4:12." Expressed as a percentage, the slope would be 33%, which is equal to 4 divided by 12. Also known as the Pitch of a roof.
Roof System: Multiple roof components assembled to provide waterproofing (and sometimes insulating) capabilities for a structure.
Run: The horizontal dimension of a slope.
Sag: Settling or drooping of base flashings that have not been properly secured to a surface.
Saturated Felt: Felt that has been saturated with bitumen.
Scrim: Woven or nonwoven material used to reinforce membranes; it is usually laminated or coated to produce the membrane.
Scuttle: A unit that provides access to the roof from the interior of the building. See also Hatch.
Sealant: Generic term for a multitude of materials used to seal joints or junctures against moisture or weather.
Sealer: Coating designed to prevent bleedout or bleed-through.
Seam: A line, ridge, or groove formed from fitting, joining, or lapping two sections together.
Self-Adhering Membrane: A type of membrane whose bottom surface will stick or adhere to a substrate without the use of an additional adhesive material.
Self-Sealing Shingle: Asphalt shingles with adhesive strips that will soften and stick to the following course of shingles when heated by the sun; used to help against wind uplift.
Selvage Edge: That portion of a granule-surfaced membrane that is designed to be overlapped by the following membrane course; usually two, four, or nineteen inches in width.
Shed Roof: A roof with only one sloping plane. Also known as Half Gable.
Shingle: (1) A single piece of prepared roofing material, either asphalt or wood, for use in steep slope roof systems. (2) To install a wood or asphalt shingle roof system.
Tab: The portion of an asphalt shingle that is outlined by the cutouts.
Tapered Edge Strip: Tapered insulation strip used to ease transitions from one substrate elevation to another and to provide slope along roof perimeters.
Tape: See Joint Tape
Tar: A brown or black bituminous material, liquid or semi-solid in consistency.
Tar Boil: A small bubble found in the flood coat of an aggregate-surfaced built-up roof; usually the result of trapped moisture vapor. Tar Boils are also known as blueberries or blackberries.
Tear-Off: To remove a roof system down to the structural substrate.
Tear Strength: The strength necessary to tear a material.
Tensile Strength: The amount of longitudinal pulling stress that a material can withstand before being pulled apart.
Termination: The sealed edges of a roof membrane.
Termination Bar: A bar, usually metal or vinyl, used to seal and anchor the free edges of a roof membrane.
Terne: Sheet iron or steel plated with an alloy of three or four parts of lead to one part of tin, used as a roofing material.
Terra Cotta: A semifired ceramic clay used in building construction.
Thatch Roof: A roof covering made with straw, palms, reeds or other natural growths that are bound together in order to shed water.
Thermal Barrier: Material used in conjunction with polyurethane foam that is designed to inhibit the rise in temperature of the foam during a fire in order to delay the foam’s involvement in the fire. Time ratings for thermal barriers should exceed 15 minutes.
Thermal Insulation: A material used to reduce heat flow.
Thermal Movement: Movement of a material resulting from temperature changes.
Thermal Resistance (R): The measure of a material’s ability to resist heat flow. The formula for Thermal Resistance is R = L / k where (L) is the material’s thickness and (k) is the material’s Thermal Conductivity constant. The higher a material’s R-value, the better it insulates, and conversely.
Thermal Shock: The damage to a roof resulting from expansion and contraction which are the result of sudden extreme temperature changes. Thermal Shock often occurs when a cold rain shower suddenly cools a roof during a hot day.
Thermoplastic: (1)Becoming soft when heated and hard when cooled. (2)A thermoplastic resin, such as polystyrene or polyethylene.
Thermoset: A material that cannot be reshaped or formed by heating. EPDM and Butyl are thermosets.
Throat: (1) The cutout of a shingle. (2) The narrowing passage located between a fireplace and smoke chamber or flue.
Tie-In: The joining of two different roof systems.
Tie-Off: A watertight seal used to terminate roof membranes at system adjuncts, terminations, flashings, or substrates. Can be temporary or permanent.
Toggle Bolt: A bolt with a separate toggle end that can be flattened to fit through a pre-drilled hole and that springs outward to provide securement when the bolt is tightened.
Tongue and Groove: Premanufactured materials with a convex "tongue" on one side and a concave "groove" on the other so that pieces of material can be joined together by placing the tongue of one piece into the groove of an adjacent piece so that the pieces fit more securely together.
Torque: Force applied to an object, particularly, to screw a mechanical fastener into a roof deck or substrate.
TPA: Tri-Polymer Alloy.
Traffic: Any rooftop activity that can potentially damage the roof surface.
Transverse Seam: The joint between the top of one metal roof panel and the bottom of the next panel, which runs perpendicular to the roof slope.
Underlayment: A material installed over the roof deck prior to the application of the primary roof covering. Usually consists of fifteen (15#) or thirty (30#) pound organic felt but can also be self-adhering such as an ice and water protection membrane.
Uplift: See Wind Uplift.
Valley: The internal intersection of two sloping roof planes that runs from the eaves to the ridge. This intersection collects the most water run-off. See Open Valley, Closed-Cut Valley and, Woven Valley
Vapor Migration: The natural movement of water vapor from regions of higher vapor pressure to regions of lower vapor pressure.
Vapor Pressure: The pressure at which a liquid and its vapor are in equilibrium at a definite temperature.
Vapor Retarder: A material used to restrict the passage of water vapor through a roof assembly.
Veneer: Any of the thin layers of wood glued together to make plywood.
Vent: An opening or device used to permit air or vapors to exit an enclosed structure.
Ventilation Short Circuit: The disruption of air flow in an intake-exhaust ventilation system. For instance, if vents such as turbine vents or gable vents are placed in between the intake vents and exhaust vents (such as soffit and ridge vents) then the draw created by the Stack Effect will be disrupted and the ventilation system will be much less effective.
Ventilator: A device that circulates fresh air and expels stale air.
Verge of Popcorn Texture: A rough surface texture of Sprayed Polyurethane Foam generally considered unsuitable to receive a base coating. Nodules on this surface are larger than the valleys and an additional 50% or more of coating material is necessary to properly cover and protect the surface.
Viscosity: The resistance of a material to heat flow.
Viscous: Having a fairly high resistance to heat flow.
Void: An open space or a break in continuity; a gap.
Volatile: That which readily vaporizes; evaporates quickly.
Vulcanize: To improve the strength, resiliency, and freedom from stickiness and odor of rubber, for example, by combining with sulfur or other additives in the presence of heat and pressure
Water Absorption: The increase in weight of a test specimen expressed as a percentage of its dry weight after being immersed in water for a specified time at a given temperature.
Water Guard: A turned up edge on valley metal or continuous wall flashing; used to prevent water migration under the roof system.
Water Stop: Material placed over a joint and used to prevent water entry.
Waterproof: Being resistant to moisture infiltration.
Waterproofing: The treatment of a surface or structure in order to prevent the passage of water under hydrostatic pressure.
Weather: To undergo degradation in quality and appearance which is caused by exposure to the sun, wind, rain, etc.
Wind Clip: A clip that slips over the ends of tile, slate and other steep slope roofing materials in order to help prevent wind uplift damage.
Wind Uplift: (1) The upward displacement of a section of a roof system or component caused by movement of air from a location of higher air pressure, such as inside a building, to an area of lower air pressure, such as the surface of a roof during a windy day. Strong wind across the surface of a roof, especially at corners and along perimeters, creates low air pressure above the surface of the roof. Nature will automatically try to compensate for this by moving air from an area of higher pressure such as inside a building. If all penetrations and perimeters are not properly sealed, then "blow-off" can occur.
(2) Displacement or blow-off of shingles or other roofing caused by the wind.
Windward: Facing into the wind..
Woven Valley: A valley construction whereby the valley has a woven look which is effected by overlapping alternate courses of shingles from both sides of the valley.
Z Bar or Z Section: A piece of steel formed in the shape of a "Z."
Zinc: A bluish-white, lustrous metallic element that is brittle at room temperature but malleable with heating. It is used to form a wide variety of alloys including brass, bronze, various solders, and nickel silver, in galvanizing iron and other metals, for electric fuses, anodes, and meter cases, and in roofing, gutters, flashings, edge metals and also for various household objects.
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