Adhesion:
The condition where two surfaces are bonded together by interfacial forces. These forces may involve molecular attraction, mechanical interlocking, or both.
Aggregate:
A collection of materials like rock, stone, crushed slag, water-worn gravel, or marble chips, used to cover or weigh down a roofing system.
Aging:
The natural changes that occur in materials over time when exposed to environmental conditions.
Alligatoring:
Cracking of the surface bitumen on a built-up roof, creating a pattern that resembles an alligator’s hide. These cracks may or may not penetrate the full depth of the surfacing.
Asbestos:
A naturally occurring group of fibrous minerals once commonly used to reinforce roofing products.
Asphalt, Air Blown:
Asphalt modified by blowing air through molten material at high temperatures, raising its softening point and changing other properties.
Asphalt Emulsion:
A mixture of asphalt particles suspended in water with the help of an emulsifying agent like bentonite clay, created through chemical or mechanical blending.
Asphalt Felt:
A felt material saturated or coated with asphalt, commonly used in roofing systems.
Asphalt Roof Cement:
A thick, trowel-applied mix of solvent-based bitumen, mineral stabilizers, and fillers. Classified by ASTM standards for roofing cements.
ASTM:
The American Society for Testing and Materials — an organization that sets technical standards for roofing and construction materials.
Atactic Polypropylene:
A type of polymer created by the polymerization of propylene, often used to modify roofing materials.
Ballast:
Heavy materials like aggregate or concrete pavers used to secure single-ply roofing membranes using the force of gravity.
Base Flashing:
Strips of roof membrane material used to seal areas where the roof meets vertical surfaces like walls. Base flashing covers the edge of the main roof membrane. (See also: Flashing.)
Base Ply:
The bottom layer of a multi-ply roofing system.
Base Sheet:
A saturated, coated, or impregnated felt sheet installed as the first layer in some built-up or modified bitumen roofing systems.
Batten:
(1) A cap or cover; (2) A metal closure that covers joints between roof panels; (3) A wood strip attached to the roof deck to support tiles; (4) A plastic, wood, or metal strip used to fasten roofing membranes or flashings.
Bitumen:
(1) A group of sticky, black, or dark-colored substances (solid, semi-solid, or liquid) made of high-molecular-weight hydrocarbons, found in asphalt, coal tar, and similar materials.
(2) A general term for materials like asphalt or coal tar used in roofing.
Blister:
A trapped pocket of air, water, or solvent vapor between layers of roofing felt, membrane, or between the membrane and its substrate.
Bridging:
(1) When a membrane is unsupported at a joint;
(2) In steep-slope roofing, it refers to installing metric-sized shingles over standard-sized ones without removing the originals.
Buckle:
An upward, tent-like distortion of a roof membrane, often over insulation or deck joints, indicating movement within the roofing system.
Built-Up Roof Membrane (BUR):
A continuous, semi-flexible roofing system made by layering felts or fabrics with alternating layers of bitumen. Typically finished with a mineral surfacing or coating.
Cant:
A beveled edge, typically foam, installed at a right-angle joint to strengthen the transition and allow water runoff.
Cant Strip:
A triangular or beveled strip (wood, perlite, fiberboard, etc.) placed where the roof deck meets a vertical surface, helping ease the transition for roofing membranes.
Cap Flashing:
Usually made of metal, this flashing covers and protects the top edges of membrane flashings or wall flashings from weather exposure. (See also: Flashing and Coating.)
Cap Sheet:
A granule-surfaced roofing sheet used as the top layer of built-up or modified bitumen roof systems.
Caulking:
(1) The act of sealing joints or seams;
(2) Material used to make joints watertight by filling gaps between roofing components.
Chalking:
A powdery residue that forms on surfaces like paints or coatings when ingredients break down and migrate to the surface.
Coated Base Sheet:
A base felt that’s first saturated with asphalt, then coated again with a heavier, more viscous asphalt for better moisture resistance.
Coated Felt (Sheet):
(1) Asphalt-saturated felt that is coated on both sides with harder asphalt;
(2) Glass fiber sheets that are impregnated and coated with asphalt.
Cold Process Built-Up Roof:
A multi-ply roofing system created by applying felts or fabrics with cold (non-hot) adhesive or cement, typically solvent-based and applied at ambient or slightly warm temperatures.
Condensation:
The process where water vapor turns into liquid as temperatures fall or atmospheric pressure increases. (See also: Dew Point.)
Coping:
The protective cap or covering installed on top of a wall, usually made of metal, masonry, or stone, and sloped to direct water back onto the roof.
Counterflashing:
A piece of metal flashing embedded into or attached to a wall, curb, or other structure to cover and protect the top edge of base flashing from weather.
Course:
(1) A single horizontal row of roofing material, like shingles;
(2) A layer in a series of waterproofing or flashing materials.
Coverage:
The area that a specific amount of roofing material will cover, usually expressed in square feet.
Cricket:
A small, elevated roof structure built to divert water around chimneys, curbs, or other roof projections. (See also: Saddle.)
Curb:
(1) A raised structure supporting roof penetrations like skylights or HVAC units;
(2) A low raised perimeter on a roof.
Deck:
The structural surface under the roofing system that must support the weight of the roof, foot traffic, and environmental loads. Can be metal, wood, or concrete.
Deflection (Bowing, Sagging):
The downward bending or sagging of a structural member or roof system under load.
Degradation:
Deterioration of a material’s chemical structure, physical properties, or appearance due to exposure to environmental factors like sunlight, moisture, or pollution.
Delamination:
The separation of bonded layers within a material or roof system.
Drain:
An outlet device installed on a roof to collect and channel rainwater away from the roof surface. (See NRCA Construction Detail “W-1.”)
Drip Edge:
A metal flashing with a projecting lower edge that directs water away from the underlying building components and helps prevent water from creeping back under the roofing.
Eave:
The edge of a roof that extends beyond the exterior wall.
Efflorescence:
White, chalky deposits formed on masonry surfaces when water evaporates and leaves behind mineral salts.
Elastomeric:
A material with elastic, rubber-like properties that can stretch and return to its original shape.
End Lap:
The area where one roofing piece overlaps the end of another.
EPDM:
Ethylene Propylene Diene Monomer — a type of durable synthetic rubber commonly used in single-ply roofing membranes.
Exhaust Ventilation:
Ventilation systems that allow warm or moist air to exit the attic or roof space, typically installed near the ridge or high points of a roof.
Expansion Joint:
A structural separation between building sections that allows movement without causing damage to the roofing or waterproofing system.
Fabric:
A woven cloth (organic or synthetic) used as reinforcement in roofing membranes and flashings.
Fascia:
The vertical board installed along the roof edge (eave or rake) that often caps the ends of rafters or provides support for gutters.
Fasteners:
Mechanical devices like nails, screws, clips, and bolts used to secure roofing materials to the deck or structural members.
Felt:
A flexible roofing sheet made from fibers (organic, fiberglass, or polyester) that are interlocked through mechanical processing, moisture, and heat. Felts are typically saturated or coated with asphalt.
Field of the Roof:
The main central area of a roof, excluding perimeter edges, curbs, and flashings.
Field Seam:
The joint created when two pieces of roofing membrane are overlapped and bonded together on-site, typically with adhesive, splicing tape, or heat welding.
Fishmouth:
A half-conical opening or wrinkle in a lap joint, often caused by shifting or wrinkling of roofing materials during installation.
Flange:
The projecting edge on components like metal flashings, skylight frames, or structural members that overlaps or fastens to adjacent surfaces.
Flashing:
Material (typically metal or membrane) used to waterproof and seal edges, penetrations, and transitions on a roof, such as around walls, chimneys, and valleys.
Gable:
The triangular upper part of a wall located between the edges of intersecting roof slopes.
Gable-Shaped Roof:
A roof that has a single ridge and slopes downward on two sides, ending in vertical gable walls.
Galvanized Steel:
Steel that has been coated with a layer of zinc to protect it from corrosion.
Gauge:
The thickness measurement of sheet metal used in roofing systems.
Glass Felt:
A roofing sheet made from bonded glass fibers, commonly used for reinforcement in bituminous roofing materials.
Granule:
Crushed rock or ceramic particles that are applied to the surface of roofing products like shingles or cap sheets to provide color and protection from UV rays.
Heat Welding:
A method of fusing thermoplastic or elastomeric roofing membranes together by applying heat (usually with hot air or open flame) and pressure to create a strong bond.
Hip:
The external angle formed where two sloping roof planes meet. It runs from the eave to the ridge.
Humidity:
The amount of moisture present in the air, typically expressed as a percentage called relative humidity (RH), which compares the current moisture level to the maximum possible at a given temperature.
HVAC:
An acronym for Heating, Ventilation, and Air Conditioning — mechanical systems that control indoor climate and air quality.
Inorganic:
Materials that originate from minerals and do not contain carbon, such as concrete or metals. Inorganic materials are not derived from plant or animal sources.
Insulation:
Materials installed within a building envelope to slow the transfer of heat, improving energy efficiency and indoor comfort. (See also: Thermal Insulation.)
Intake Ventilation:
The fresh air brought into an attic or roof cavity, usually through soffit or eave vents, that helps balance airflow in a passive ventilation system.
Lap:
The overlapping portion where roofing or waterproofing components cover part of an adjacent piece to maintain weatherproof integrity.
Lap Seam:
A seam formed when overlapping roofing materials are bonded together using adhesives, tape, heat, or solvents.
Lead:
A soft, workable metal used primarily for flashing details, particularly around penetrations.
Life Cycle Costing:
An economic analysis method that considers the total cost of a product or system over its expected useful life, including installation, maintenance, repairs, and disposal.
Mansard:
A decorative steeply sloped roof that encircles the perimeter of a building, often designed to improve aesthetics or create additional usable attic space.
Mansard Roof:
A type of roof with two slopes on each side — the lower slope is steeper and almost vertical, while the upper slope is much shallower and often flat at the top.
Mat:
A thin layer of woven, non-woven, or knitted fibers used as reinforcement within roofing membranes or other construction materials.
Material Safety Data Sheets (MSDS):
Documents provided by manufacturers that outline the chemical composition, hazards, safe handling practices, and emergency measures related to a product, as required by OSHA regulations.
Mechanically-Fastened Membranes:
Roof membranes that are secured to the substrate using mechanical devices like plates, battens, screws, or nails at specified intervals.
MIL:
A unit of measurement equal to one-thousandth of an inch (0.001 inches), commonly used to describe the thickness of roofing membranes.
Mineral-Surfaced Roofing:
Roofing materials where the surface layer is covered with mineral granules, providing durability and UV protection.
Mineral-Surfaced Sheet:
A sheet of roofing material, often asphalt-based, that is surfaced with mineral granules for added protection and appearance.
Modified Bitumen:
A type of asphalt that has been enhanced with polymers (such as Atactic Polypropylene [APP] or Styrene-Butadiene-Styrene [SBS]) to improve flexibility, durability, and resistance to extreme temperatures.
Moisture Scan:
A diagnostic technique using devices like capacitance meters, infrared cameras, or nuclear gauges to detect trapped moisture within a roof system without invasive procedures.
Mopping:
The application of hot bitumen to a roof surface or membrane using a mop or mechanical applicator.
Types of Mopping:
- Solid Mopping: A continuous, uniform application of bitumen across the surface.
- Spot Mopping: Bitumen is applied in circular spots, leaving unmapped areas between.
- Sprinkle Mopping: Bitumen is sprinkled randomly across the surface.
- Strip Mopping: Bitumen is applied in straight, parallel strips.
Mud Cracking:
The pattern of surface cracking that resembles dried, cracked mud, often occurring when a roofing material shrinks or degrades.
Net Free Vent Area:
The total area of unobstructed vent openings, measured in square inches, allowing unrestricted airflow into or out of a space.
NRCA (National Roofing Contractors Association):
A leading trade association for roofing professionals, providing industry standards, educational resources, and advocacy.
Organic:
Materials composed of carbon-based compounds originating from living organisms, such as plant fibers.
Penetration:
(1) Any object that passes through the roof, like pipes or vents.
(2) A measure of the hardness of bitumen, expressed as how far a standard needle can penetrate into the material under specific conditions.
Permeance:
The rate at which water vapor passes through a material. It’s typically measured in grains per square foot per hour per inch of mercury (grain/ft²·h·inHg).
Phased Application:
The process of installing components of a roofing or waterproofing system in stages over time, rather than all at once. (Note: Surfacing applied at different times usually isn’t considered phased.)
Picture Framing:
The visible pattern of insulation boards or deck joints telegraphing through the roof membrane, often caused by movement of the underlying materials.
Plastic Cement:
A thick, trowelable asphalt-based compound used for sealing and repairing roofs, typically on low-slope surfaces.
Ply:
A single layer of felt, sheet, or reinforcement within a built-up roof membrane.
Polyester:
A synthetic fiber material used to reinforce roofing membranes, valued for its strength and flexibility.
Polyurethane Foam (SPF): A spray-applied roofing material that expands into a solid, seamless surface, providing insulation, waterproofing, and durability in a single system.
Primer:
(1) A thin, liquid layer (often solvent-based) applied to a surface to improve adhesion of subsequent materials.
(2) Used in seaming single-ply membranes to enhance bond strength.
PVC (Polyvinyl Chloride):
A type of durable, flexible plastic material often used for single-ply roofing membranes.
Rake:
The inclined edge of a roof that runs from the eave up to the ridge, typically at the gable end of a building.
RCI (Roof Consultants Institute):
A professional organization for roofing, waterproofing, and building envelope consultants. (Now called IIBEC – International Institute of Building Enclosure Consultants.)
Re-Cover:
Adding a new roof membrane over most or all of an existing roof without removing the old roofing materials.
Reroofing:
The complete removal and replacement of an existing roof system.
Reglet:
A slot or groove (usually in masonry or concrete) designed to receive and hold counterflashing.
Reflective Humidity:
The ratio (expressed as a percentage) of the moisture content of air to the maximum moisture the air could hold at the same temperature.
Replacement:
The removal of the existing roofing system down to the deck and installation of a completely new system.
Ridge:
The highest horizontal point where two sloping roof planes meet, running along the roof’s peak.
Ridge Vent:
A ventilation product installed at the roof ridge that allows warm, moist air to escape from the attic or rafter space.
Roof Curb:
A raised frame installed on the roof to support mechanical equipment, skylights, or other rooftop structures.
Roof Jack:
A metal bracket used to secure toe boards (safety boards) on steep-slope roofs during installation.
Roof Overhang:
The portion of the roof that extends beyond the exterior walls of a building, providing shade and protection from rain.
Roof Slope:
The angle of the roof surface compared to a horizontal plane. It’s usually expressed as a ratio, like 4:12 (4 inches of rise for every 12 inches of horizontal run).
Roof System:
The complete assembly of interacting roof components — usually including a membrane or primary covering and insulation — designed to protect a building from the elements.
Saddle:
A small, raised structure (similar to a miniature roof) built between drains or behind projections to divert water toward drainage points. (Also called a cricket.)
SBS (Styrene-Butadiene-Styrene):
A rubber-like polymer added to asphalt to create flexible, durable modified bitumen roofing materials.
Sealant:
A material (often rubber or bitumen-based) used to seal joints where slight movement is expected, providing waterproofing and weatherproofing protection.
Seam:
A joint where two separate pieces of roofing material are joined together, typically using adhesives, heat welding, solvent welding, or tapes.
Selvage Edge:
The unsurfaced portion along the edge of certain roofing sheets (like mineral-surfaced sheets) that allows for better adhesion during overlapping installation.
Side Lap:
The overlap along the sides (lengthwise) of two adjacent roofing sheets or panels.
Single-Ply Membranes:
Roofing systems that use just one layer of flexible membrane (either homogeneous or composite) instead of multiple layers.
Single-Ply Roofing:
A roofing system with a single flexible membrane layer, often made of thermoset, thermoplastic, or modified bitumen materials.
Skylight:
A transparent or translucent roof accessory that admits natural light into the building’s interior, typically mounted on a raised frame or curb.
Slip Sheet:
A protective sheet (like kraft paper or polyethylene) placed between two roof components to prevent sticking, chemical damage, or abrasion.
Smooth Surfaced Roof:
A roof surface without any embedded mineral granules or aggregate — usually coated with a smooth asphalt or other membrane.
Soil Stack:
A vertical pipe that vents plumbing fixtures through the roof to the outside air.
Solvent:
A liquid used to dissolve or thin other materials (like adhesives or coatings) that evaporates during the drying or curing process.
Split:
A straight-line rupture or tear in roofing material, typically caused by tensile (pulling) forces.
Square:
A common roofing measurement equal to 100 square feet of roof area.
Standing Seam:
A type of metal roof where adjoining panels are joined by raised, interlocking seams that stand vertically above the roof surface.
Substrate:
The surface over which the roofing or waterproofing system is applied — often a structural deck, insulation layer, or existing roof.
Sump:
A recessed area around a roof drain or scupper, designed to help funnel and promote proper water drainage off the roof.
Surfacing:
The top layer of a roofing system, installed to protect the underlying materials from weather, UV radiation, and physical damage.
Test Cut:
A small section cut out of an existing roof system to inspect and diagnose its condition — checking for membrane type, number of plies, moisture presence, and bitumen application rates.
Thermal Shock:
Stress and potential damage caused by sudden, extreme temperature changes — for example, a roof surface exposed to hot sunlight followed by a cold rain.
Thermoplastic:
A type of material that becomes soft and flexible when heated and hardens when cooled, without losing its chemical properties. This heating and cooling process can be repeated.
Thermoset:
A material that permanently hardens when heated. Unlike thermoplastics, once set, it cannot be remelted or reshaped.
UL (Underwriters Laboratories, Inc.):
An independent organization that tests and certifies the safety and performance of building products, including roofing materials.
UN Label:
A certification label, authorized by Underwriters Laboratories, indicating that a roofing product meets specific performance and safety standards.
Underlayment:
A layer of material (typically asphalt-saturated felt or synthetic sheet) installed between the roof deck and the roof covering, providing a secondary barrier against water intrusion.
Valley:
The internal angle formed where two sloping roof planes meet, creating a channel for water runoff.
Vent:
An opening in the roof or wall of a building that allows air, moisture, or gases to escape to the outside atmosphere.
Void:
An open space or gap within roofing materials that can lead to weak points or potential leaks.
Waterproof:
The quality of a material or membrane that prevents the passage of water under normal conditions.
Wind Uplift:
The upward pressure on a roof caused by wind blowing over and around it, which can lift roofing materials if they aren’t properly secured.