Roofing Dictionary

The following is a dictionary of basic roofing terms from the NRCA Roofing and Waterproofing Manual.
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ICBO: International Conference of Building Officials.
Ice dam: a mass of ice formed at the transition from a warm to a cold roof surface, frequently formed by refreezing meltwater at the overhang of a steep roof, causing ice and water to back up under roofing materials.

Ice dam protection membrane: a continuous membrane installed under steep slope roofing materials in areas subject to ice damming that prohibits water which gets through the roof covering from getting into the structure.
Must also seal the fasteners that penetrates it.

Ignition temperature: the lowest temperature at which combustion will occur spontaneously under specific conditions.

Impact resistance: resistance to fracture under the sudden application of an exerted force.

Impregnate: In roofing materials manufacture, to completely surround the fibers in a felt or mat with bitumen, with the spaces between the fibers partially or completely filled without a continuous coating of bitumen on the surface.

Infrared thermography: The process of displaying variations of apparent temperatures (variation of temperature or emissivity or both) over the surface of an object by measuring variations in infrared radiance.

Inorganic: being or composed of materials other than hydrocarbons and their derivatives, or matter that is not of plant or animal origin.

Insect screen: wire mesh used to prevent insects from entering the building through ventilators, louvers, or other openings.

In-service R-value: thermal resistance value established under installed conditions and measured over the expected service life of the material.
The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 989

Insulation: any of a variety of materials designed to reduce the flow of heat, either from or into a building. (see also Thermal insulation.)

Intake ventilation: the fresh air that is drawn into a passive ventilation system through vents typically installed in the soffit or eave of a roof.

Interlayment: a felt, metal, or membrane sheet material used between courses of steep-slope roofing to improve the weather- and water-shedding characteristics of the primary roof covering during times of wind-driven precipitation. Typically used with wood shakes.

Interlocking shingles: individual shingles that mechanically attach to each other to provide enhanced wind resistance without reliance on sealing strips.

Inverted roof membrane assembly (IRMA™): a patented, proprietary variation of the “protected membrane roof assembly” in which Styrofoam® brand insulation and ballast are placed over the roof membrane. IRMA™ and Styrofoam® are registered trademarks of the Dow Chemical Company.

ISANTA: International Staple, Nail & Tool Association

Isocyanate: a highly reactive organic chemical containing one or more isocyanate (-N=C=0) groups. A basic component in SPF based systems and some polyurethane coating systems.

Isolation sheet: refer to slip sheet.


Joist: any of the small timbers, metal or wood beams arranged parallel to each other and spanning from wall to wall to support a floor, ceiling, or roof of a building.

Joule: a unit of energy or work; equals the work done by a force of 1 newton which acts over a distance of 1 meter in the direction of the force.


k or k-Value: thermal conductivity; the time rate of heat flow through a unit area of a homogeneous material in a direction perpendicular to isothermal planes induced by a unit temperature gradient. In English (inch-pound) units of measurement, it is the number of BTUS that pass through a 1 inch (25 mm) thickness of a 1 square foot (0.09 m2) sample of material in 1 hour with a temperature difference between the two surfaces of 1° F. It is expressed as Btu•inch/h•ft2•°F.

Kerf: (1) a slit or notch made by a saw or cutting torch; (2) the width of cut made by a saw or cutting torch.

Kesternich test: simulates acid rain conditions by subjecting test specimens to a sulfur dioxide atmosphere as well as condensing moisture for the purpose of evaluating rust/corrosion characteristics.

Knee cap: a metal cover trim that fits over a panel rib after it has been cut and bent.

Knee joints: see Knuckle.

Knuckle: a metal closure, either shop-or pre-fabricated, installed over the cut seam of a continuous metal roof panel at the transition from a steep-slope roof to a vertical roof or wall.


Laitance: a weak layer of cement and aggregate fines on a concrete surface that is usually caused by an overwet mixture, overworking the mixture, improper or excessive finishing or combination thereof.

Laminate: to join layers of materials together using fusion; the process of joining layers of materials together using adhesion.

Laminated shingles: see Dimensional shingles or Architectural shingles.

Lap: that part of a roofing, waterproofing, or flashing component that overlaps or covers any portion of the same or another type of adjacent component.

Lap cement:
an asphalt-based roof cement formulated to adhere overlapping plies or asphalt roll roofing. The NRCA Roofing and Waterproofing Manual—Fifth Edition 990 Glossary

Lap seam: occurs where overlapping materials are seamed, sealed or otherwise bonded.

Latex: a stable dispersion of polymeric substance in an essentially aqueous medium.

Lead: a soft malleable, heavy metal; has low melting point and a high coefficient of thermal expansion.

Leader head: see Conductor head.

Lift: the sprayed polyurethane foam that results from a pass. It usually is associated with a certain pass thickness and has a bottom layer, center mass and top skin in its makeup.

Liquid-applied: application of bituminous cements, adhesives or coatings installed at ambient or slightly elevated temperatures.

Liquid-applied built-up roof: a continuous, semi-flexible roof membrane, consisting of multiple plies of felts, mats or fabrics laminated together with alternate layers of roof cements and surfaced with a liquid -applied coating with or without aggregate surfacing.

Live loads: temporary loads that the roof structure must be designed to support, as required by governing building codes. Live loads are generally moving and/or dynamic or environmental, (e.g., people, installation equipment, snow, ice or rain, etc.).

Loose-laid membrane: a ballasted roofing membrane that is attached to the substrate only at the edges and penetrations through the roof.

Low-slope roofs: a category of roofs that generally include weatherproof membrane types of roof systems installed on slopes at or less than 3:12 (14 degrees).

Low temperature flexibility: the ability of a membrane or other material to resist cracking when flexed after it has been cooled to a low temperature.


Mansard: a decorative steep-sloped roof on the perimeter of a building.

Mansard roof: a steeper roof that terminates into a flat roof at its high point.

Masonry: construction, usually set in mortar, of natural building stone or manufactured units, such as brick, concrete block, adobe, glass block, tile, manufactured stone or gypsum block.

Mastic: a thick adhesive material used as a cementing agent for holding waterproofing membrane in place. (see Asphalt roof cement).

Mat: a thin layer of woven, non-woven, or knitted fiber that serves as reinforcement to a material or membrane.

Mat slab: a concrete slab designed with reinforcement to resist the uplift forces created by hydrostatic pressure.

Material safety data sheets (MSDS): a written description of the chemicals in a product and other pertinent data, including such things as safe handling and emergency procedures. In accordance with OSHA regulations, it is the manufacturer’s responsibility to produce an MSDS and the employers responsibility to communicate its contents to employees.

Mechanical damage:
in SPF-based roofing, physical damage to a completed SPF-based roof system not caused by normal wear and tear.

Mechanically fastened membranes: generally used to describe membranes that have been attached at defined intervals to the substrate.

Membrane: a flexible or semi-flexible roof covering or waterproofing whose primary function is to exclude water.

Metal: any of various opaque, fusible, ductile and typically lustrous substances that are good conductors of electricity and heat. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 991

Metallic waterproofing: consist of finely graded iron particles combined with an oxidizing catalyst. When mixed with water (or water, cement, and sand), the finely distributed particles expand, creating a waterproof layer that becomes a part of the surface to which it is applied.

Metal rain collar: a metal counterflashing used to wrap a penetration and prevent water infiltration though the top of the penetration base flashing.

Meter: unit of length measurement in the metric system; 1 meter is equal to 39.37 inches.

Metal roof panel: an interlocking metal sheet having a minimum installed weather exposure of 3 square feet (279000 mm2 or 0.28 m2) per sheet.

Metal roof shingle: an interlocking metal sheet having an installed weather exposure less than 3 square feet (279000 mm2 or 0.28 m2) per sheet.

Mil: a unit of measure, one mil is equal to 0.001 inches, or 25.4 micrometers (µm), often used to indicate the thickness of a roofing membrane.

Mildew: a superficial growth produced on organic matter or living plants by fungi.

Millimeter: a unit of measure equal to one thousandth (0.001) of a meter, or 0.03937 inches.

Mineral fiber: insulation composed principally of fibers manufactured from rock, slag or glass, with or without binders.

Mineral granules: see Granules.

Mineral stabilizer: a fine, water-insoluble inorganic material, used in a mixture with solid or semi-solid bituminous materials.

Mineral-surfaced roofing: roofing materials whose surface or top layer consists of a granule-surfaced sheet.

Mineral-surfaced sheet: a roofing sheet that is coated on one or both sides with asphalt and surfaced with mineral granules.

Miter joint: a joint between two members at an angle to each other; each member is cut at an angle equal to half the angle of the junction; usually the members are at right angles to each other.

Model (building) codes: a compilation of standards or codes established to provide uniformity in regulations pertaining to building construction.

Modified bitumen: (1) a bitumen modified by including one or more polymers (e.g., atactic polypropylene, styrene butadiene styrene, etc.); (2) composite sheets consisting of a polymer modified bitumen often reinforced with various types of mats or films and sometimes surfaced with films, foils or mineral granules.

Moisture contour map: a map used to graphically define the location of moisture within a roof assembly after a moisture scan has been performed.

Moisture relief vent: a venting device installed through the roofing membrane to relieve moisture vapor pressure from within the roofing system.

Moisture scan: the use of a mechanical device (capacitance, infrared, or nuclear) to detect the presence of moisture within a roof assembly. (see Non-destructive testing.)

Mole run: a meandering ridge in a roof membrane not associated with insulation or deck joints.

Monolithic: formed from or composed of a single material; seamless.

Monomer: a low-molecular-weight substance consisting of molecules capable of reacting with like or unlike molecules to form a polymer.
The NRCA Roofing and Waterproofing Manual—Fifth Edition
992 Glossary

Mop-and-flop: an application procedure in which roofing elements (insulation boards, felt plies, cap sheets, etc.) are initially placed upside down adjacent to their ultimate locations; coated with adhesive or bitumen; and turned over and adhered to the substrate.

Mopping: the application of hot bitumen with a mop or mechanical applicator to the substrate or plies of a bituminous
membrane. There are four types of mopping.

• Solid mopping: a continuous coating.

• Spot mopping: bitumen is applied roughly in circular areas, leaving a grid of unmopped perpendicular areas.

• Sprinkle mopping: bitumen is shaken onto the substrate from a broom or mop in a random pattern.

•Strip mopping: bitumen is applied in parallel bands.

Mud cracking: surface cracking resembling a dried mud flat.

Mud slab: a layer of concrete, typically 2 inches (50 mm) to 6 inches (150 mm) thick, used as the substrate for membrane waterproofing.


Nailer: (sometimes referred to as blocking) a piece or pieces of dimensional lumber and/or plywood secured to the structural deck or walls, which provide a receiving medium for the fasteners used to attach membrane or flashing.

NBP: acrylonitrile butadiene polymer blend. One proprietary NBP membrane is commonly referred to as nitrile butadiene copolymer.

Negative side waterproofing: an application wherein the waterproofing system and source of hydrostatic pressure are on opposite sides of the structural element.

Neoprene: a synthetic rubber (polychloroprene) used in liquid and sheet-applied elastomeric roof membranes or flashings.

Nesting: (1) the installation of new metal roof deck directly on top of existing metal roof deck; (2) a method of reroofing with new asphalt shingles over existing shingles in which the top edge of the new shingle is butted against the bottom edge of the existing shingle.

Net free vent area: the area (measured in square inches) open to unrestricted air flow and commonly used as a yardstick to measure relative vent performance; the area of the opening of a vent minus the area displaced by the screening material.

Newton (N): SI unit of measure for force.

Night seal (or night tie-in): a material and/or method used to temporarily seal a membrane edge during construction to protect the roofing assembly in place from water penetration. Usually removed when roofing application is resumed.

NIST: National Institute of Standards and Technology

Nitrile alloy: an elastomeric material of synthetic nonvulcanizing polymers.

Nitrile rubber: a membrane whose predominant resinous ingredient is a synthetic rubber made by the polymerization of acrylonitrile with butadiene.

Noble metal: a metal that readily receives electrons from an anodic metal (see Galvanic series).

No-cutout shingles: shingles consisting of a single solid strip with no cutouts.

Nondestructive testing (NDT): a method to evaluate the disposition, strength or composition of materials or systems without damaging the object under test. Typically used to evaluate moisture content in roofing assemblies, the three common test methods are electrical capacitance, infrared thermography and nuclear back-scatter. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 993

Nonflammable: not easily ignited and not burning rapidly if ignited.

Nonfriable: a material that, when dry, cannot be crumbled, pulverized or reduced to powder by hand pressure.

Nonoxidizing: a material which resists oxidation in exterior exposures or accelerated weathering.

Non-traffic bearing: for waterproofing purposes, a membrane system requiring some form of protection barrier and wearing surface.

Nonvolatile content: the portion of a coating that does not evaporate during drying or curing under specified conditions, comprising the binder and, if present, the pigment. (The percent volatile content is obtained by subtracting the nonvolatile content from 100.).

Nonwoven fabric: a textile structure produced by bonding or interlocking of fibers, or both, accomplished by mechanical, chemical, thermal, or solvent means and combinations thereof.

NRCA: National Roofing Contractors Association.

Nuclear hydrogen detection (NHD) meter: a device that contains a radioactive source to emit high velocity neutrons into a roof system. Reflecting neutrons are measured by a gauge that is used to detect hydrogen; the quantity of hydrogen detected may be linked to the pressure of water.

Nylon: generic name for a family of polyamide polymers, used as a scrim in some fabric-reinforced sheeting.


Off-ratio foam: SPF that has excess isocyanate or resin. Off-ratio will not exhibit the full physical properties of normal SPF.

Open time: the period of time after an adhesive has been applied and allowed to dry, during which an effective bond can be achieved by joining the two surfaces.

Open valley: a method of valley construction in which the steep-slope roofing on both sides are trimmed along each side of the valley, exposing the metal valley flashing.

Orange peel surface texture: in SPF roofing, a condition of the foam in which the surface shows a fine texture and is compared to the exterior skin of an orange. This surface is considered acceptable for receiving a protective coating.

Organic: being or composed of hydrocarbons or their derivatives, or matter of plant or animal origin.

Organic felt: an asphalt roofing base material manufactured from cellulose fibers.

Organic shingle: an asphalt shingle reinforced with material manufactured from cellulose fibers.

ORNL: Oak Ridge National Laboratory.

Osmosis: movement of a solvent through a semipermeable membrane into a solution of higher solute concentration that tends to equalize the concentration of solute on the two sides of the membranes.

Overflow drainage: component in a roof drainage system used to protect the roof against damage from a water load imposed by blocked or partially blocked primary drainage system; e.g., overflow scupper, overflow interior

Overspray: undesirable depositions of airborne spray.

Overspray surface texture: in SPF roofing, a condition of the foam in which the surface shows a linear coarse textured
pattern and/or a pebbled surface. This surface is generally downwind of the sprayed polyurethane path and, if severe, unacceptable for proper coating coverage and protection.

Ozone: a triatomic form of oxygen that is a bluish gas of pungent odor; is formed naturally in the upper atmosphere by a photochemical reaction with solar ultraviolet radiation. The NRCA Roofing and Waterproofing Manual—Fifth Edition 994 Glossary

Ozone resistance: the ability of a material to resist the deteriorating effects of ozone exposure.


Pallet: a platform (typically wooden) used for storing and shipping materials.

Pan: the bottom flat part of a roofing panel that is between the ribs of the panel.

Pan former: power roll-forming equipment that produces a metal roofing panel from a flat sheet.

Parapet wall: the part of a perimeter wall that extends above the roof.

in masonry construction, a coat of cement mortar on the face of rough masonry, the earth side of foundation and basement walls, or the like.

Partially attached: a roofing assembly in which the membrane has been “spot affixed” to a substrate, usually with an adhesive or a mechanical device.

Parting agent: a material applied to one or both surfaces of a sheet to prevent blocking.

Pascal: SI unit of measure for force per unit area; 1 Pa=1 N/m2.

Pass: (1) a layer of material, usually applied by the spray method, that is allowed to reach cure before another layer (“pass”) is applied; (2) a term used to explain a spray motion of the foam gun in the application of the spray polyurethane foam (SPF) material. The speed of the pass controls the thickness of the SPF.

Pass line: the junction of two passes of SPF. A distinct line is formed by the top skin of the bottom pass and the next pass adhering to this skin.

Pedestal: a support or base for roof top components such as pavers, pipes and small roof top units.

Peel strength: the average load per unit width required to separate progressively a flexible member from a rigid member or another flexible member.

Penetration: (1) any construction (e.g., pipes, conduits, HVAC supports) passing through the roof; (2) the consistency of a bituminous material expressed as the distance, in tenths of a millimeter (0.1 mm), that a standard needle penetrates vertically into a sample of material under specified conditions of loading, time, and temperature.

Perlite: an aggregate used in lightweight insulating concrete and preformed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass.

Perm: see Permeance.

Permeability: (1) the capacity of a porous material to conduct or transmit fluids; (2) the time rate of vapor transmission through unit area of flat material of unit thickness induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions. The English (inch•pound) unit of measurement for permeability is gr/hr•ft2•(in. Hg/in.), which is commonly referred to as “perm•inch” units.

Permeance: (1) the rate of water vapor transmission per unit area at a steady state through a material, membrane, or assembly; (2) the time rate of water vapor transmission through unit area of flat material or construction induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions. The English (inch•pound) unit of measurement for permeance is gr/h•ft2•in. Hg, which is commonly referred to as “perm” units.

pH: a measure of the acidity or alkalinity of a solution, with neutrality represented by a value of 7, with increasing acidity represented by increasingly smaller values, and with increasing alkalinity represented by increasingly larger values.

Phased application: the installation of a roofing or waterproofing system during two or more separate time intervals or different days. Application of surfacings at different time intervals are typically not considered phased application. (see Surfacing.) A roofing system not installed in a continuous operation. The NRCA Roofing and Waterproofing Manual—Fifth Edition
Glossary 995

Picture framing: a square or rectangular pattern of ridges in a roof membrane or covering over insulation or deck joints.

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.

Pipe boot: prefabricated flashing piece used to flash around circular pipe penetrations.

Pitch: see Coal tar.

Pitch-pocket (Pitch-pan): a flanged, open bottomed enclosure made of sheet metal or other material, placed around a penetration through the roof,
filled with grout and bituminous or polymeric sealants to seal the area
around the penetration.

Pittsburgh lock seam: a method of interlocking metal, usually at a slope change.

Plastic cement: a roofing industry generic term used to describe asphalt roof cement that is a trowelable mixture of solvent-based bitumen, mineral stabilizers, and other fibers and/or fillers. Generally, intended for use on relatively low slopes, not vertical surfaces. (also see Asphalt roof cement and Flashing cement.)

Plasticizer: a material incorporated in a material to increase its ease of workability, flexibility or distensibility.

Plasticizer migration: in some thermoplastic roofing membranes, the loss of plasticizer chemicals from the membrane, resulting in shrinkage and embrittlement of the membrane, typically PVC.

Pliability: the material property of being flexible or moldable.

Ply: a layer of felt or ply sheet in a built-up roof membrane or roof system.

PMR: protected membrane roof.

Polychloroprene: see Neoprene.

Polyester: a polymer in which the repeated structural unit in the chain is of the ester type. Polyisobutylene (PIB): a product formed by the polymerization of isobutylene. May be compounded for use as a roof membrane material.

Polymer: a macromolecular material formed by the chemical combination of monomers having either the same or different chemical composition.

Polymer modified bitumen: see Modified bitumen.

Polymeric methylene diphenyl diisocyanate (PMDI): component A in SPF. An organic chemical compound having two reactive isocyanate groups. It is mixed with the B component to form polyurethane.

Polymerization: a chemical reaction in which monomers are linked together to form polymers.

Polypropylene: a polymer prepared by the polymerization of propylene as the sole monomers.

Polyol: a polyhydric alcohol, i.e., one containing three or more hydroxyl groups, one component of polyisocyanurate and polyurethane compounds.

Polyvinyl chloride (PVC): a synthetic thermoplastic polymer prepared from vinylchloride. PVC can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, fillers and other modifiers. Rigid forms are used in pipes; flexible forms are used in the manufacture of sheeting and roof membrane materials.

Polystyrene: a polymer prepared by the polymerization of styrene as the sole monomer.

Pond: a surface which is incompletely drained. The NRCA Roofing and Waterproofing Manual—Fifth Edition 996 Glossary

Ponding: the excessive accumulation of water at low-lying areas on a roof that remains after the 48 hours after the end rainfall under conditions conducive to drying.

Pop rivet: a relatively small-headed pin with an expandable head for joining light gauge sheet metal.

Popcorn surface texture: in SPF roofing, the condition in which the foam surface shows a coarse texture where valleys form sharp angles. This surface is unacceptable for proper coating and protection.

Positive drainage: the drainage condition in which consideration has been made during design for all loading deflections of the deck and additional roof slope has been provided to ensure drainage of the roof area within 48

hours following rainfall during conditions conducive to drying.

Positive side waterproofing: an application where the waterproofing systems and the source of the hydrostatic pressure are on the same side of the structural element.

Pot life (Working life): the period of time during which a reacting composition remains suitable for its intended processing after mixing with reaction initiating agents .

Pourable sealer: a type of sealant often supplied in two parts and used at difficult-to-flash penetrations, typically in conjunction with pitch-pockets to form a seal.

Press brake: a machine used in cold-forming sheet metal or strips of metal into desired profiles.

Prestressed concrete: concrete in which the reinforcing cables, wires or rods in the concrete are tensioned before there is load on the structural member, holding the concrete in compression for greater strength.

Pre-tinning: coating a metal with solder or tin alloy prior to soldering or brazing it.

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 that 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; (3) a thin liquidap plied material that may be applied to the surface of SPVF to improve the adhesion of subsequent application of SPVF protective coatings.

Proportioner: the basic pumping unit for SPF or two-component coating systems. Consists of two positive displacement pumps designed to dispense two components at a precisely controlled ratio.

Protection course: a sacrificial material used to shield a waterproofing material from damaging external forces.

Protection mat: a sacrificial material used to shield one roof system component from another.

Protected membrane roof (PMR): an insulated and ballasted roofing assembly in which the insulation and ballast are applied on top of the membrane (sometimes referred to as an “inverted roof assembly”).

Psychrometer: an instrument used to measure humidity in the atmosphere from two thermometers which are similar
except that the bulb of one is kept wet, the bulb of the other being dry.

Psychrometric chart: chart showing the relationship between dew point temperature, dry bulb temperature, wet bulb temperature and relative humidity.

Puncture resistance: the ability of a material to withstand the action of a penetrating or puncturing object.

Purlin: horizontal secondary structural member that transfers loads from the primary structural framing.

PVC: polyvinyl chloride.