Glossary of roofing terms

KETTLE A portable device for heating asphalt.

LAP That part of a roofing membrane which overlaps or covers any portion of another section of membrane which is then sealed to form a watertight connection.

LOOSE-LAID MEMBRANE A ballasted, single ply roofing membrane that is attached to the substrate only at the building edges and penetrations through the roof.

LUGGER A device for moving hot asphalt across a roof surface.

MAT A thin layer of woven, non-woven, or knitted fiber which serves as reinforcement to the membrane.

MB Abbreviation for "Modified Bitumen."

MESH The square opening of a sieve. Also, an open weave material used as a reinforcement in bituminous, cold process applications.

METAL FLASHING See FLASHING; frequently used as through-wall, cap, or counterflashing.

MIL A unit of measure used to indicate the thickness of a roofing membrane. One rail is equal to 0.001 inches or 25,400 microns (0.0254 ram).

MINERAL GRANULES Opaque, natural, or synthetically colored aggregate commonly used to surface cap sheets, granule-surfaced sheets and roofing shingles.

MINERAL STABILIZER A fine, water-insoluble, inorganic material, used in admixture with solid or semi-solid bituminous materials.

MINERAL-SURFACED ROOFING Built-up roofing whose top ply consists of a granule-surfaced sheet.

MINERAL-SURFACED (CAP) SHEET A felt that is coated on one or both sides with asphalt and surfaced with mineral granules.

MODIFIED BITUMEN A material consisting of asphalt which has been modified through the inclusion of one or more polymers and may contain stabilizers and other additives. Modified bitumen roofing membranes may also contain a reinforcing material.

MOLE RUN A meandering ridge in a membrane not associated with insulation or deck joints.

MOP-AND-FLOP A procedure in which roofing elements (insulation boards, felt plies, cap sheets, etc.) are initially placed upside down adjacent to their ultimate locations, are coated with adhesive, and are then turned over and adhered to the substrate.

MOPPING The application of hot asphalt with a mop or mechanical applicator to the substrate or to the plies of a bituminous roof. There are four types of mopping:
(1) Solid - a continuous coating;
(2) Spot- asphalt is applied in spots, leaving a grid of unmopped, perpendicular areas;
(3) Strip - asphalt is applied in parallel bands, generally 8 inches (203 ram) wide and 12 inches (305 mm) apart; (4) Sprinkle - asphalt is shaken onto the substrate from a broom or mop in a random pattern.

MUD CRACKING Surface cracking resembling a dried mud flat. Alligatoring

NAILER A piece of dimension lumber or plywood secured to the structural deck or walls, which provides a receiving medium for the fasteners used to attach the membrane or flashing. Nailers must be the same thickness as the insulation, and should be treated with a non-oil-borne preservative.

NEOPRENE Elastomeric membranes made by the polymerization of chloroprene (polychloroprene).

NIGHT SEAL A material used to temporarily seal a membrane edge during construction to protect the roofing assembly in place from water penetration. (Also CUTOFF.)

NINETY-POUND A prepared roll roofing with a granule-surfaced exposure that has a mass of approximately 90 Ibs./108 ft2 (4.05 kg/m2).

NON-VULCANIZED MEMBRANE A membrane manufactured from thermoplastic compounds that has not been heat cured and retains its thermoplastic properties throughout the life of the membrane.

NON-WOVEN A term used to describe the random arrangement of reinforcing fibers (glass, polyester, etc.) in a mat or scrim.

NRCA Abbreviation for "National Roofing Contractors Association."

OPEN TIME The period of time during which an effective bond can be achieved by joining two surfaces after a contact adhesive has been applied and allowed to dry.

ORGANIC Any chemical or chemical compound which is composed of, or which contains carbon.

PARTING AGENT A material applied to one or both surfaces of a sheet to prevent sticking.

PEEL STRENGTH The average force (or force per unit width) required to peel a membrane from the substrate to which it has been bonded.

PERLITE BOARD An insulation board containing perlite, a volcanic ore which when heated, expands and becomes a good insulator.

PHASED CONSTRUCTION The installation of a roofing or water proofing system during two or more separate time intervals; a roofing system not installed in a continuous operation. Also known as PHASE APPLICATION, PHASING.

PIB Abbreviation for "polyisobutylene."

PIPE BOOT Prefabricated flashing used to flash around circular pipe penetrations.

PICTURE FRAMING (1) A rectangular pattern of ridges in a membrane over insulation or deck joints. (2) A method of providing additional attachment around the perimeter of a building, usually on SPM mechanically attached systems.

PINHOLE A tiny hole in a film, foil, or laminate comparable in size to one made by a pin.

PITCH POCKET An enclosure made of sheet metal, rubber, or other material, used to flash penetrations through a roof system. Also known as pitch pan and PENETRATION PAN.

PLASTIC CEMENT A generic term used to describe a utility asphalt roof cement intended for use on low slopes.

PLASTICIZER A chemical substance (e.g., an organic compound) added to natural or synthetic resins for the purpose of increasing flexibility, and facilitating processing and workability.

PLY A layer of felt in a bituminous roofing membrane; a four-ply membrane has at least four plies of felt at any vertical cross section cut through the membrane.

POLYISOCYANURATE INSULATION A rigid foam roof insulation board produced from polyisocyanurate based chemicals. Also commonly referred to as isocyanurate or "iso".

PONDING The surface accumulation of water in low-lying or poorly drained areas of a roof. If ponding is excessive, the weight may result in a load which exceeds the design capacity of the structure, or possibly cause premature deterioration of the membrane.

POURABLE SEALER A specific type of sealant used at difficult-toflash penetrations, typically in conjunction with "pitch pockets" to form a weathertight seal.

PRIMER A thin liquid applied to a surface to improve the adhesion of heavier applications of hot or cold adhesives and to absorb dust.

PROTECTED ROOFING MEMBRANE ASSEMBLY (PRMA) An insulated, and ballasted roofing assembly, in which the insulation and ballast are applied on top of the membrane. Sometimes called an "inverted assembly" or an "upside down roof."

PVC Abbreviation for "polyvinyl chloride."

RACKING To stretch or strain by force. Also diagonal wrinkles in flashing materials which indicate differential movement between deck and wall.

RAG FELT Now, a generic term referring to an organic felt. Formerly, a roofing felt composed of mainly cotton rag fibers.

RAGGEL A groove or slot, often cut in a masonry wall or other vertical surface adjoining a roof, for inserting an inset flashing component such as a reglet.

RASPBERRY See STRAWBERRY.

REGLET A groove in a wall or other surface adjoining a roof surface for the attachment of counterflashing.

RELEASE AGENT See PARTING AGENT.

REROOFING The process of replacing an existing roofing system.

RETRO-FIT ROOFING The process of recovering an existing roofing system. Also - OVERLAY

RESISTANCE, THERMAL The measurement of the resistance to heat flow.

RIDGING An upward, tenting displacement of a membrane, frequently over an insulation joint.

RIEI Abbreviation for "Roofing Industry Educational Institute," a non-profit educational institute dedicated to increasing and disseminating knowledge about roofing technology.

ROLL ROOFING Coated felts, either smooth or mineral-surfaced.

ROOF CEMENT See FLASHING CEMENT, PLASTIC CEMENT.

ROOF VENT A vertical outlet in a built-up roofing system to relieve the pressure exerted by water vapor between the roofing membrane and the vapor retarder or deck.

ROOFING SYSTEM An assembly of interacting components designed to weatherproof, and normally to insulate, a building's top surface.

RUBBER A material that is capable of recovering from large deformations quickly and forcibly, and can be, or already is, modified to a state in which it is essentially insoluble (but can swell) in boiling solvent such as benzene, methyl ethyl ketone, and ethanol-toluene azeotrope.

SADDLE A small structure that helps to channel surface water to drains. Frequently located in a valley, a saddle is often constructed like a small hip roof, or like a pyramid with a diamondshaped base. (Also CRICKET.)

SATURATED FELT A felt that that has been immersed in hot asphalt and has absorbed as much asphalt as it can retain under the processing conditions.

SCRIM A woven, non-woven, or knitted fabric, composed of continuous strands of material used for reinforcing or strengthening felts or membranes. Scrim may be incorporated into the membrane by laminating, coating or extruding.

SCUFFING IN The practice of sealing the edges of a bituminous cap sheet by applying foot pressure along the lap.

SCUTTLE A hatch that provides access to the roof from the interior of the building.

SEAM A joint formed by mating together two separate sections of single ply roofing membrane. Seams may be sealed in a variety of ways, including hot-air welding, solvent welding and adhesive bonding.

SEAM STRENGTH The force or stress required to separate or rupture a seam in the membrane material.

SEAM TAPE Cured or uncured synthetic rubber tape used for splicing in lieu of "contact adhesives."

SELF-ADHESIVE MEMBRANE Single ply membrane which can adhere to a substrate and to itself at overlaps without the use of a field-applied adhesive.

SELVAGE A specially defined edge of a material designed for some special purpose such as overlapping or seaming.

SHARK FIN An upward-curled felt sidelap or endlap.

SHEAR STRENGTH The stress (pounds [N] or pounds per inch width) required to disrupt a lap seam or bonded joint or attachment by forcing the substrates to slide over each other,

SHINGLE (1) A small unit of prepared roofing designed for installation with similar units in overlapping rows on inclines normally exceeding 25%; (2) To cover with shingles; (3) To apply any sheet material in overlapping rows like shingles.

SINGLE PLY ROOFING A roofing system in which the principal roofing component is a single ply flexible membrane.

SLAG A grayish, porous aggregate left as a residue from blast furnaces and used as surfacing aggregate.

SLIP SHEET Sheet material, such as reinforced kraft paper, polyester scrim, or polyethylene sheeting, placed between two components of a roofing system (such as membrane and insulation) to ensure that no adhesion occurs between them, and to prevent possible damage from chemical incompatibility.

SLOPE The angle of incline of a roof surface as measured in inches per foot (mm/m).

SOFTENING POINT The temperature at which asphalt becomes soft enough to flow as determined by an arbitrary, closely defined test method.

SOLID MOPPING See MOPPING.

SOLVENT CLEANERS Heptane, hexane, white gas, and unleaded gas, used to clean the membrane prior to applying the splicing adhesive in some single ply roofing systems.

SOLVENT WELDING A process used to chemically weld or join together two or more layers of certain membrane materials (usually thermoplastic) by applying a solvent, such as tetra-hydrofuran (THF), to the overlapping surfaces and mating them when the bonding surfaces become tacky. Used most often in welding or sealing seams.

SPLICE See SEAM.

SPLIT A membrane rupture resulting from tensile stress.

SPOT MOPPING See MOPPING.

SPRINKLE MOPPING See MOPPING.

SPUD To remove the roofing aggregate and most of the bituminous top coating by scraping and chipping.

SQUARE A roof area of 100 ft2 (9.29 m2), or enough material to cover 100 ft2 (9.29 m2) of substrate.

STEEP ASPHALT A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type III.

STRAWBERRY A small bubble or blister in the flood coating of a gravel-surfaced membrane.

STRIP MOPPING See MOPPING.

STRIPPING (1) The technique of sealing a joint between metal and membrane with one or two plies of felt, fabric or membrane and hot- or cold-applied adhesive; (2) The technique of taping joints between insulation boards or deck panels.

STYRENE-BUTADIENE-STYRENE RUBBER (SBS) High molecular weight polymers having rubber-like properties, formed by the random copolymerization of styrene and butadiene monomers. Polymers of this type are often crosslinked to give maximum rubberlike properties in service. These polymers are sometimes used as the modifying compound in certain modified bitumen roofing membranes.

SUBSTRATE The surface upon which the roofing or waterproofing membrane is placed.

SUMP A depression in the surface of a roof around the opening to a drain, which serves to promote drainage.

SUPER-STEEP ASPHALT A roofing asphalt conforming to requirements of ASTM Specification D 312, Type IV. Also known as SPECIAL STEEP ASPHALT.

TAPERED EDGE STRIP A tapered insulation strip used to elevate the roofing at the perimeter and at penetrations of the roof.

TAR See COAL TAR PITCH.

TAR BOLLS Bubbles of moisture vapor encased in a thin film of asphalt. Also blueberry, strawberry or raspberry.

TEAR OFF To remove an existing roofing system down to the structural deck.

TEAR RESISTANCE The load required to tear a material when the stress is concentrated on a small area of the specimen by the introduction of a prescribed flaw. Expressed in pounds force (N) or pounds per lineal inch.

TENSILE STRENGTH The maximum force or stress required to break a membrane sample during a tensile test.

THERMAL INSULATION A material applied to retard the flow of heat.

THERMAL SHOCK The stress-producing phenomenon resulting from sudden temperature drops in a roof membrane when, for example, a rain shower follows brilliant sunshine.

THERMOPLASTIC Polymers which soften when heated and harden when cooled. This process is reversible provided the material is not heated above the point at which decomposition occurs.

THERMOSET A material that solidifies or "sets" irreversibly when heated. This property is usually associated with crosslinking of the molecules induced by heat or radiation.

THROUGH-WALL FLASHING A water-resistant membrane or material assembly extending totally through a wall and its cavities, positioned to direct any water within the wall to the exterior.

ULTIMATE ELONGATION The amount a material stretches during tensile testing before it ruptures, usually expressed as a percentage of the original length.

UMBRELLA See BONNET.

UNDERWRITERS LABORATORIES (UL) An independent, non-profit agency which functions as the testing arm of the National Board of Fire Underwriters. It maintains laboratories for the examination and testing of various devices, systems, and materials to determine their safety against the hazards of fire and accident. UL is organized around a number of separate departments, including "Chemical Hazards," "Electrical Hazards," and "Fire Protection."

VAPOR RETARDER Sheet material installed to impede or restrict the passage of water vapor through a roofing assembly.

VENT An opening designed to convey water vapor or other gas
from inside a building or a building component to the atmosphere. (Also ROOF VENT.)

VERMICULITE An aggregate used in lightweight insulating concrete, formed by heating and expanding a micaceous mineral.

VOID An absence of adhesive between two layers of membrane.

WALK IN To embed insulation panels in hot asphalt or
adhesive by walking on them immediately after application.

WATER CUTOFF MASTIC A thermoset material used to form a seal between single ply membrane sheets at indicated termination points.

WATER VAPOR TRANSMISSION A measure of the rate of transmission of water vapor through the membrane material under controlled laboratory conditions of temperature and humidity.

WIND SCOURING Erosion of ballast or surfacing due to wind.

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