Roofing Glossary

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Blanca R.
11/26/2019

Understanding Roofing Terminology

Some companies prefer that their customers know as little as possible about their roofs. But at Tip Top Roofing, Inc. we know that the more information you have, the better decision you will make about your home or businesses roofing system. We are straight forward about our products and processes we use and we want to be your roofing contractor for the long term, not for just one job.

Terms And Phrases You Should Know When Discussing Your Roof

3-tab Shingle: An asphalt shingle comprised of a single layer with the exposed area separated by cut-outs into three tabs that are approximately 12” to 36”.

Abrasion Resistance: The ability to resist being worn away by contact with another moving, abrasive surface, such as foot traffic, mechanical equipment, wind-blown particles, tree limbs, etc.

A-component (A-side): One component of a two-component polymer system; for polyurethane foam and coatings, the isocyanate component.

Acrylic Coating: A coating system based on acrylic binders dispersed in water (occasionally in solvents) with pigments and several proprietary additives that cures by coalescence and air drying.

Adhere: Two types of roofing materials need to stick together or adhere to each other. In the case of built-up roofing, the adhesive material is asphalt, while single-ply membranes uses contact cement.

Adhesion: (1) The degree of attachment between two surfaces held together by interfacial forces—mechanical, chemical or both; (2) The degree of attachment or bonding between application of the same substance; (3) The combined ultimate strength of the molecular forces and the mechanical interlocking achieved between the adhesive and the surface bonded. Adhesion is measured in shear and peel modes.

Adhesive: A cementing substance that produces a steady and firm attachment or adhesion between two surfaces.

Algae: Rooftop fungus that can leave dark stains on roofing.

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.

Architectural Shingle: An asphalt shingle made up of multiple layers. The tabs on these shingles are cut to different sizes and shapes to give the roof a more three-dimensional appearance. Also called dimensional or laminated shingles.

Asphalt: A bituminous waterproofing material applied to roofing materials during manufacture.

Asphalt Emulsion: Asphalt particles mixed with an emulsifying agent such as bentonite clay and water.

Asphalt Primer: A thin liquid bitumen applied to a surface to improve the adhesion of self-adhering membranes and to absorb dust.

Asphalt Roof Cement: An asphalt-based cement used to bond roofing materials. Also known as flashing cement or mastic.

Asphalt Shingle: A shingle created by covering a fiberglass mat with an asphalt-based coating, then adding mineral granules to the surface. One of the most common residential roofing materials, it is known for its durability and ease of installation.

Ballast: Ballast materials (like precast concrete or aggregate) use gravity to hold a single-ply roofing in place.

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 ply.

Base Flashing: That portion of the flashing attached to or resting on the deck to direct the flow of water onto the roof covering.

Base Sheet: A product intended to be used as a base ply in a self-adhering roll roofing system.

Batten: A strip of wood usually fastened to the structural deck for use in attaching a primary roof system such as tile.

B-component (B-side): One component of a two-component polymer system; for polyurethane foam and coatings, the resin component.

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.

Blisters: Bubbles that may appear on the surface of asphalt roofing after installation. These occurrences are usually moisture related.

Bond: (1) The adhesive and/or cohesive forces holding two components in positive contact; (2) A surety; typical types are: bid, performance and payment; (3) A guarantee relating to roof system performance.

Boot: A piece of material preformed to protect roof penetrations from dirt, moisture and other foreign and/or damaging substances.

Built-up Roof (BUR): A flat or low-sloped roof consisting of multiple layers of ply sheets embedded in hot asphalt.

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.

Bundle: A package of shingles. There are typically 3, 4 or 5 bundles per square.

Butt Joint: A joint formed by adjacent, separate sections of material, such as where two neighboring pieces of insulation abut.

Cap Sheet: A mineral surfaced material that is used by itself or as the top layer of multi-layer rolled roof covering system.

Caulking: (1) The physical process of sealing a joint or juncture; (2) Sealing and making weather-tight the joints, seams, or voids between adjacent units by filling with a sealant.

Cement: Adhesives used to adhere or bond roofing components.

Cladding: A material used to cover the exterior wall of a building.

Closed Cut Valley: A method of valley treatment in which shingles from one side of the valley extend across the valley while shingles from the other side are trimmed 2” from the valley centerline. The valley flashing is not exposed.

Coated Base Sheet: An asphalt-saturated base sheet membrane later coated with harder, more viscous asphalt, thereby increasing its impermeability to moisture.

Coating: A layer of material spread over a surface for protection or decoration.

Collar: Also called “vent sleeve”, is a pre-formed flange placed over a vent pipe to seal the roof around the vent pipe opening.

Condensation: The change of water from vapor to liquid when warm, moisture-laden air comes in contact with a cold surface.

Cool Roof: A roof system that uses products made of highly reflective and emissive materials for its top surface. Cool roof surfaces can remain at markedly lower temperatures when exposed to solar heat in service than surfaces of roofs constructed with traditional non-reflective roofing products.

Cool Roof Shingle: Shingles that are specially designed to remain at lower temperatures than traditional, non-reflective shingles when exposed to the sun's rays, which may reduce attic temperature and help save on cooling costs.

Coping: The covering piece on top of a wall, which is exposed to the weather usually made of metal, masonry, or stone. It is preferably sloped to shed water back onto the roof.

Counterflashing: That portion of the flashing attached to a vertical surface to prevent water from migrating behind the base flashing.

Course: A row of shingles or roll roofing running the length of the roof.

Coverage: The number of layers of material between the exposed surface of the roofing and the deck; i.e., single coverage, double coverage, etc.

Cricket: A device that helps divert water around or away from chimneys and other large roof projections.

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 8″ in height; (2) A raised roof perimeter that is relatively low in height.

Cure: A process whereby a material is caused to form permanent molecular linkages by exposure to chemicals, heat, pressure, and/or weathering.

Cure Time: The time required to effect curing. The time required for a material to reach its desirable long-term physical characteristics.

Decking: The structural material over which roofing is applied. Usually plywood, boards, or planks.

Delamination: Separation of the laminated layers of a component or system.

Dimensional Shingle: Another name for an architectural shingle.

Dormer: A small, raised roof area protruding from the roof plane, usually housing a window.

Downspout: Also called a “leader”, is a pipe for draining water from roof gutters.

Drain: The device that collects and directs the flow of runoff water from a roof area.

Drainage System: Prefabricated materials that facilitate the drainage of water away from the structure.

Drip Edge: Rigid material that is installed at the edge of the roof to keep shingles off the deck, extending them out over eaves and gutters. This helps control the direction of dripping water that could damage underlying components.

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.

Durability: The ability to withstand physical, chemical or environmental abuse.

Eave: The edge of a roof that overhangs the wall.

Eave Flashing: Additional layer of roofing material applied at the eaves to help prevent damage from water back-up.

Elasticity: Properties of a material that will permit it to return to its original shape after being stretched.

Elastomeric Coating: A coating that can be stretched to twice its dimensions and that will return to original when tension is released.

Embedment: To uniformly press one material into another, such as aggregate into bitumen, roofing felt into bitumen, or granules into a coating.

Emulsion: (1) A bituminous emulsion is a mixture of asphalt and water with uniform dispersion of the bitumen or water globules, usually stabilized by an emulsifying agent (clay or soap) or system; (2) A relatively stable mixture of two immiscible liquids held in suspension by small amounts of emulsifiers.

Erosion: (1) Weathering, wearing away or degradation; (2) Wearing a way of a coating by chalking or the abrasive action of water or windborne particles or grit.

Expansion: The increase in length or volume of a material or body caused by temperature, moisture or other environmental conditions.

Expansion Joint: A structural separation between two building elements that allows free movement between the elements without damage to the roofing or waterproofing system.

Exposure: The portion of the membrane that is not overlapped by the succeeding ply or course. Or, the portion of the roofing exposed to the weather after installation.

Extrusion: A manufacturing process which consists of forcing batched and formulated material (which may be molten) through an orifice called a “die.” The shape and dimensions of the orifice determine the shape and dimensions of the finished product. Extrusion is one method by which some single-ply roofing membranes are manufactured.

Fascia OR Fascia Board (pronounced fey-shuh): Horizontal trim at the eaves that covers the rafter ends.

Fasteners: Any of a wide variety of mechanical securement devices and assemblies, including nails, screws, cleats, clips, and bolts, which may be used to secure various components of a roof assembly.

Felt: Fibrous material saturated with asphalt and used as an underlayment or sheathing paper.

Fiberglass Base Sheet: A fiberglass-reinforced base sheet for built-up roof system construction, impregnated and coated with asphalt and surfaced with mineral matter.

Fiberglass Mat: The core material in an asphalt roofing shingle manufactured from glass fibers.

Field of the Roof: The central or main portion of a roof, excluding the perimeter and flashing.

Flame Retardant: A substance which is added to a polymer formulation to reduce or retard its tendency to burn.

Flange: The projecting edge of a rigid or semi-rigid component, such as a metal edge-flashing flange, skylight flange, flashing boot, structural member, etc.

Flashing: A material installed around a roof penetration or along an edge to help keep moisture from seeping into the layers below. Can be found along the roof's perimeter or at penetrations, walls, expansion joints, valleys, drains, and other places where the roofing is interrupted or terminated.

Flashing Collar: Also called “roof jack” or “flashing boot”, is an accessory flashing used to cover and/or seal soil pipe vents and other penetrations through the roof.

Flashing Cement: As used by the roofing industry, roof cement that is a trowelable mixture of solvent-based bitumen and mineral stabilizers that may include asbestos or other inorganic or organic fibers. Generally, flashing cement is characterized as vertical-grade, which indicates it is intended for use on vertical surfaces.

Foam Stop: The roof edge treatment upon which spray polyurethane foam is terminated.

Gable: The upper triangular portion of a sidewall that comes to a point at the ridge of a double sloping roof.

Gable roof: A traditional roof style in which two roof planes meet at the ridge line.

Granules: Ceramic-coated colored crushed rock that is applied to the exposed surface of asphalt roofing products.

Gutter: The trough that channels water from the eaves to the downspouts.

HVAC: Heating, ventilation and air conditioning systems are referred to as HVAC. It’s an integral component to any residential or commercial structure, as it regulates temperature and provides comfort. These systems can also affect indoor air quality. Air filters must be cleaned and replaced regularly to ensure good performance and durability of the entire system.

Hip: The inclined external angle formed by the intersection of two sloping roof planes. Runs from the ridge to the eaves.

Hip Roof: A roof with four roof planes coming together at a peak and four separate hip legs.

Hood: A cover, usually of light-gauge metal, over piping or other rooftop equipment.

Humidity: The amount of moisture contained in the atmosphere. Generally expressed as percent relative humidity (the ratio of the amount of moisture [water vapor] actually present in the air, compared to the maxi-mum amount that the air could contain at the same temperature.)

Insulation: Any of a variety of materials designed to reduce the flow of heat from or into a building.

Interlocking Shingles: Individual shingles that mechanically fasten to each other to provide wind resistance.

Isocyanate: A highly reactive organic chemical containing one or more isocyanate groups. A basic component in spray polyurethane foam systems and some polyurethane coating systems.

Joist: Metal or wood beams arranged parallel from wall to wall to support a building’s floor, ceiling or roof.

Laminated Shingles: Shingles containing more than one layer to create extra thickness. Also called “3-dimensional shingles” or “architectural shingles”.

Lap: To cover the surface of one shingle or roll with another.

Liquid-applied: Application of bituminous, polymer-modified bitumen or polymeric roof and waterproofing membranes, flashings, cements, adhesives or coatings installed at ambient or slightly elevated temperatures.

Liquid-applied Roof Membrane: A continuous roof membrane constructed in place with a liquid resin and reinforcing material. It is available as a one- or two-component product and typically is applied in two coats.

Mastic: A thick adhesive material used as a cementing agent for holding waterproofing membrane in place.

Mechanically Damage: In roofing, physical damage to a roof system not caused by normal wear and tear.

Membrane: A flexible or semiflexible roof covering or waterproofing whose primary function is to exclude water.

Mil: A unit of measure, one mil is equal to 0.001” or 25.400 microns, often used to indicate the thickness of a roofing membrane.

Mildew: A superficial coating or discoloring of an organic material due to fungal growth, especially under damp conditions.

Modified Bitumen: Rolled roofing membrane with polymer modified asphalt and either polyester or fiberglass reinforcement.

Mortar: Mixture of sand, mortar, limestone and water used in bonding a chimney’s bricks together.

Open Valley: Method of valley construction in which shingles on both sides of the valley are trimmed along a chalk line snapped on each side of the valley. Shingles do not extend across the valley. The valley flashing is exposed.

OSB (Oriented Strand Board): OSB is cheaper than plywood, but not as strong as plywood, and does not hold nails as well as plywood. One side has a slip resistant coating and should be placed facing up.

Overflow Drainage: Emergency or overflow drainage devices, such as drains or scuppers, which provide for drainage relief from a roof system or waterproofing system if primary drains allow water to build up for any reason.

Overhang: That portion of the roof structure that extends beyond the exterior walls of a building.

Overspray: Undesirable depositions of airborne spray.

Parapet Wall: This is a part of a perimeter wall next to and extending above the roof.

Penetration: A penetration can refer to any break in the roofing materials, such as a vent stack, skylight, HVAC and more. It also refers to the hardness of a bituminous material, as shown by the distance a standard needle penetrates vertically into the material under specific conditions of loading, time and temperature.

Phased Application: (1) The installation of a roof or waterproofing system during two or more separate time intervals or different days. Applications of surfacing’s at different time intervals are typically not considered phased application. (2) A roof system not installed in a continuous operation.

Pigment: An insoluble compounding material used to impart color.

Pinhole: A tiny hole in a coating, film, foil, membrane or laminate comparable in size to one made by a pin.

Pitch: The degree of roof incline expressed as the ratio of the rise, in feet, to the span, in feet.

Ply: A layer of roofing (i.e., one-ply, two-ply).

Plywood: A flat panel built up of sheets of wood called veneers, united under pressure by a bonding agent to create a panel with an adhesive bond between plies as strong as or stronger than the wood. Plywood is constructed of an odd number of layers with grain of adjacent layers perpendicular. Layers may consist of a single ply or two or more plies laminated with parallel grain direction. Outer layers and all odd-numbered layers generally have the grain direction oriented parallel to the long dimension of the panel.

Polyurethane: A polymer prepared by the reaction of an organic diisocyanate with compounds containing hydroxyl groups (polyols). Polyurethanes, or urethanes as they are sometimes called, may be thermosetting, thermoplastic, rigid or soft and flexible, cellular or solid; they can be aliphatic or aromatic.

Polyurethane Coating: A one- or two-part solvent-based coating that contains polyisocyanate monomer and a hydroxyl containing resin, that reacts during cure to form elastomeric coating.

Ponding: The accumulation of water after rainfall at low-lying areas on a roof that remains wet when other parts of the roof have dried.

Positive Drainage: This refers to a roof that has been purposefully designed to add additional roof slope to ensure proper drainage of the roof area within 48 hours of a rainfall.

Primer: (1) A thin, liquid-applied solvent-based bitumen that may be applied to a surface to improve the adhesion of subsequent applications of bitumen; (2) A material which is sometimes used in the process of seaming single-ply membranes to prepare the surfaces and increase the strength (in shear and peel) of the field splice.

Radiant Barrier: A low emittance (0.1 or less) surface used in the construction of a radiant barrier system.

Rafter: The supporting framing member immediately beneath the deck, sloping from the ridge to the wall plate.

Rake: The inclined edge of a sloped roof over a wall.

Re-covering: The process of adding an additional layer of roofing over an existing layer. A maximum of two layers of any roofing type are permitted on a roof at any time.

Reflectance: Solar reflectance is the fraction of the solar energy (flux) that is reflected by the surface; reflectance is expressed as a percentage or a decimal value between 0.00 and 1.00.

Reinforced Membrane: A roofing membrane that has been strengthened by adding polyester scrims or mats, glass fibers or other material.

Replacement: The process of removing the existing roof covering, repairing any damaged substrate and installing a new roof covering; also known as "tear-off and replacement."

Re-roofing: The process of removing existing roof coverings and replacing with a new roofing system.

Resin: The “B” component in SPF that is mixed with the “A” component in order to form polyurethane. Resin contains a catalyst, fire retardants, a blowing agent, Polyol, and a surface-active agent.

Ridge: The uppermost, horizontal external angle formed by the intersection of two sloping roof planes.

Ridge Cap: Material specifically made to cover the peak ridge or hips of the roof.

Ridge Vent: An air slot cut into the roof deck at the highest point on the roof. The vent construction protects the inside from the weather while allowing air to flow freely through the attic.

Rise: The vertical distance from the eaves line to the ridge.

Roll or Rolled Roofing: Smooth-surfaced or mineral-surfaced, coated, prepared felts.

Roof Covering: The exterior roof cover or skin of the roof assembly consisting of membrane, panels, sheets, shingles, tiles, etc.

Roof Curb: Raised frame used to mount mechanical units such as air conditioning units, exhaust fans, skylights, etc., on a roof.

Roof Deck Protection: Also known as underlayment, are often synthetic or fiberglass-reinforced felts. They provide a water-shedding secondary layer of protection under the final roof covering.

Roofing System: A system of interacting roof components generally consisting of a membrane or primary roof covering and roof insulation (not including the roof deck) designed to weatherproof and sometimes improve the building's thermal resistance.

R-Value: This insulation metric is used to measure thermal resistance per unit area to determine flow of heat performance. R-value is added to material layers for walls, windows and doors to improve performance. This value is determined by dividing the warm and cold temperature differences of the surface by the amount of heat flux within the barrier.

Saddle: A relatively small raised substrate or structure constructed to channel or direct surface water to drains or off the roof. A saddle may be located between drains or in a valley, and is often constructed like a small hip roof or like a pyramid with a diamond-shaped base.

Saturated Felt: An asphalt-impregnated felt used as an underlayment between the deck and the roofing material.

Scarifying: In spray polyurethane foam roof systems, shaping by grinding.

Scupper: A drainage device in the form of an outlet through a wall, parapet wall or raised roof edge typically lined with a sheet-metal sleeve.

Sealant: (1) A material that has the adhesive and cohesive properties to form a seal; (2) A mixture of polymers, fillers and pigments used to fill and seal joints where moderate movement is expected; unlike caulk, it cures to a resilient solid.

Seam: Especially with large commercial roofs, the roofing materials cannot all be installed in one big sheet, so there will be seams where sheets or types of material overlap. Seams are the most common places for leaks to happen.

Self-Adhering: A term used to describe materials that have the ability to adhere to a variety of surfaces when contact is promoted by application of pressure but that require no substances to form the bond.

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-Adhering Shingle Underlayment: A self-adhering waterproofing underlayment designed to protect against water infiltration due to ice dams or wind driven rain.

Shading: Slight differences in shingle color that may occur as a result of normal manufacturing operations.

Sheathing: The structural material over which roofing is applied. Usually plywood, boards, or planks.

Shingle: A small piece of roofing material designed to be installed in overlapping rows or courses.

Siding: The finish covering of an exterior wall of a frame building; the siding may be a cladding material such as wood, aluminum or vinyl (but not masonry).

Silicone Coating: A liquid-applied elastomeric coating; the principal polymer in the dispersion contains more than 95% silicone resin.

Single-Ply Membranes: Roofing membranes that are applied in one layer. Thermoplastic and thermoset membranes are usually single-ply membranes. single-ply membranes come in five basic types: (1) Ballasted; (2) Fully-adhered; (3) Mechanically-fastened; (4) Partially-adhered and (5) Self-adhered. Seams of single-ply membranes can be heat welded, solvent welded, and adhered using seam tape or other adhesives.

Single-Ply Roofing: Roofing systems where the principal component consists of a single-ply membrane.

Skylight: A roof accessory designed to admit light into a living space.

Slate: A hard rock consisting mainly of clay minerals.

Slope: The steepness of the roof expressed as a ratio. For example, a 4:12 slope means there are 4" of vertical rise for every 12" of horizontal length.

Smooth-surfaced Roof: A membrane roof system that includes a weathering surface without mineral granule or aggregate surfacing.

Soffit: The exposed area under a roof eave or overhang.

Specification: A precise statement of a set of requirements to be satisfied by a material, product, system or service.

Sprayed Polyurethane Foam (SPF): A monolithic sprayed-on roofing material with a high R-value; formed when isocyanate (“A” component) and resin (“B” component) are mixed at a 1:1 ratio.

Sprayed Polyurethane Foam Alliance (SPFA): Sprayed Polyurethane Foam Alliance; a trade association of spray polyurethane foam applicators, manufacturers and distributors of polyurethane foam, equipment and protective coatings and providers of inspections, surface preparations and other services. It is an educational and technical resource and voice of the spray polyurethane industry.

Split: A membrane tear resulting from tensile stresses.

Square: A measurement of roof area equal to 100 square feet or enough roofing material to cover 100 square feet of a roof deck.

Staining: Temporary or permanent discoloration to the surface of a roof membrane, coating or other covering caused by foreign material on the surface.

Standing Seam: In metal roofing, a type of seam between adjacent sheets of material made by turning up the edges of two adjacent metal panels and then folding or interlocking them in a variety of ways.

Starter Strip or Starter Course: The first row of roofing that is installed at the edge of the eave. They are also installed along the rakes to improve the wind resistance of the roof.

Substrate: In construction a substrate has a few different meanings. It’s commonly used to refer to a material surface, such as an underlying layer, in which other substances are added. It can also be a material from the ground such as sand or materials which make up a building’s foundation. A substrate is often the base material for a protective layer.

Surfacing: (1) The top layer or layers of a roof covering specified or designed to protect the underlying roofing from direct exposure to the weather; (2) The wearing or top layer of a traffic-bearing waterproofing membrane.

Styrene: A colorless oily liquid, C6H5CH:CH2, the monomer for polystyrene.

Styrene Butadiene Styrene (SBS): The modifying agent used in SBS modified asphalt roofing materials that gives the material a rubber-like quality.

Synthetic Underlayment: An underlayment product that is typically manufactured using polypropylene and is used as an alternative to felt underlayment.

Tab: The bottom portion of a shingle, where the material is separated by the shingle cut-outs.

Tear Off: To remove an existing roofing system down to the structural deck.

Thermal Barrier: In torched membrane applications over combustible substrates, an above-deck barrier incorporated into a roof system before torching as a fire-safety practice. Acceptable thermal barriers include: minimum ¾”-thick perlite board insulation, minimum ¾”-thick fiberglass or mineral wool board insulation or minimum ¼”-thick glass-faced gypsum board.

Thermal Resistance: The quantity determined by the temperature difference at steady state between two defined surfaces of a material or construction that induces a unit heat flow rate through a unit area. (1) A thermal resistance (R) value applies to a specific thickness of a material or construction; (2) The thermal resistance (R) of a material is the reciprocal of the thermal conductance (C) of the same material (i.e., R = 1/C); (3) Thermal resistance (R) values can be added, subtracted, multiplied and divided by mathematically appropriate methods.

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.

Thermal Stress: Stress to a roof system or component caused by expansion and / or contraction from temperature change.

Tie-in: In roofing and waterproofing, the transitional seal used to terminate a roofing or waterproofing application at the top or bottom of flashings or by forming a watertight seal with the substrate, membrane, or adjacent roof or waterproofing system.

Torch-down: Designed with modified bitumen, this roofing system includes layers of fiberglass installed with a flame torch. It’s used exclusively for flat or low-slope roofs. The roofing specialist heats the rolled layer of roofing material with a hand-held propane torch to attach it to the surface. It involves melting seams together, which creates a tight seal. A torch-down roof can expand or contract without cracking.

Tongue & Groove Planks: One of the oldest types of dimensional structural wood used as roof decking. The sides are cut with convex and concave grooves so adjacent planks may join in alignment with each other to form a uniform roof deck.

Two-component System: In spray polyurethane foam roofing, a coating of polyurethane foam formed by the mixing and reaction of two different materials.

Underlayment: Also called “felt underlayment” Asphalt saturated felt or specially engineered synthetic material used beneath roofing to provide additional protection for the deck.

Unforeseen Conditions: (1) Unusual situation not reasonably anticipated based on contract documents; (2) unknown physical condition of an unusual nature that differs materially from those ordinarily encountered.

Water-shedding: The ability of individual, overlapping components to resist the passage of water without hydrostatic pressure.

Waterproof: The quality of a membrane, membrane material or other component to prevent water entry.

Waterproofing: Treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.

Valley: The place where two downward-sloping sections of a roof join, creating a "V" shaped depression.

Valley Flashing: Flashing that is used in open valleys of the roof.

Vent: An opening that allows air, heat, and water vapor from inside a building to escape to the outside.

Ventilation: The term used in roofing for the passage of air from an exposed space.

Warranty: The written promise to the owner of roofing materials for material related problems.

Waterproof Underlayment: Modified bitumen based roofing underlayment. Designed to seal to wood decks and waterproof critical leak areas.

Yield: In spray polyurethane foam roofing, the volume of foam per unit weight normally expressed as board ft per lb or board feet per 1,000 lbs.

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