Adhesion: the state in which two surfaces are held together by interfacial forces which
may consist of modular forces or interlocking action or both.
Aggregate: rock, stone, crushed stone, crushed slag, water worn gravel, or marble
chips used for surfacing and/or ballasting a roof system.
Aging: the effect on materials that are exposed to an environment for an interval
period of time.
Alligatoring: the cracking of the surfacing bitumen on a built-up roof, producing a
pattern of cracks similar to an alligator’s hide; the cracks may or may not
extend through the surfacing bitumen.
Asbestos: a group of natural, fibrous, impure silicate materials used to reinforce some
Asphalt, Air Blown: produced by blowing air through molten asphalt held at an
elevated temperature , raise the asphalt’s softening point and
modified other properties.
Asphalt Emulsion: a mixture of asphalt particles and an emulsifying agent such as
bentonite clay and water. These components are combined by using
a chemical or a clay emulsifying agent and mixing or blending
Asphalt Felt: an asphalt-saturated and/or an asphalt-coated felt. (See Felt)
Asphalt Roof Cement: a trowelable mixture of solvent-based bitumen, mineral
stabilizers, other fibers and/or fillers. Classified by ASTM
Standard 2822-91 Asphalt Roof Cement, and D 4586-92
Asphalt Roof Cement, Asbestos-Free, Types I and II.
ASTM: American Society for Testing and Materials
Atactic Polypropylene: a group of high molecular weight polymers formed by the
polymerization of propylene.
Ballast: an anchoring material, such as aggregate or precast concrete pavers, which
employs the force of gravity to hold (or assist in holding) single-ply
membranes in place.
Base Flashing: (membrane base flashing): piles or stripes of roof membrane material
used to close-off and/or seal a roof at the roof-to-vertical intersections,
such as at a roof-to-wall juncture. Membrane base flashing covers the
edge of the field membrane (Also see Flashing)
Base Ply: the lowermost ply of roofing in a roof membrane or roof system.
Base Sheet: an impregnated, saturated, or coated felt placed as the first ply in some
Mult-ply built-up and modified bitumen roof membranes.
Batten: (1) cap or cover; (2) in a metal roof;: a metal closure set over or covering the
joint between, adjacent metal panels; (3) wood: a strip of wood usually set in or
over the structural deck, used to elevate and/or attach a primary roof covering
such as a tile; (4) in a membrane roof system: a narrow plastic, wood or metal
bar which is used to fasten or hold the roof membrane and/or base flashing
Bitumen: (1) a class of amorphous, black or dark colored, (solid, semi-solid or viscous)
cementitious substances, natural or manufactured, composed principally of
high molecular weight hydrocarbons, soluble in carbon disulfide, and found
in petroleum asphalts, coal-tars and pitches, wood tars and asphalts; (2) a
generic term used to denote any material composed principally of bitumen,
typically asphalt or coal tar.
Blister: an enclosed pocket of air, which may be mixed with water or solvent vapor,
trapped between impermeable layers of felt or membrane or between the
membrane and substrate
Bridging: (1) when the membrane is unsupported at a juncture; (2) bridging in steep-
slope roofing is a method of re-roofing over standard-sized asphalt shingles
with metric-sized asphalt shingles.
Buckle: an upward, elongated tenting displacement of a roof membrane frequently
occurring over insulation or deck joints. A buckle may be an indication of
movement within the roof assembly.
Built-Up Roof Membrane (BUR): a continuous, semi-flexible multi-ply roof
membrane, consisting of piles or layers of saturated felts,
coated felts, fabrics or mats between which alternate layers
of bitumen are applied. Generally, built-up roof membranes
are surfaced with mineral aggregate and bitumen, a liquid-
applied coating or granular-surfacing cap sheet.
Cant: a beveling of foam at a right angle joint for strength and water run off.
Cant Strip: a beveled or triangular-shaped strip of wood, wood fiber, perlite or
other material designed to serve as a gradual transitional plane between
the horizontal surface of a roof deck or rigid insulation and a vertical
Cap Flashing: usually composed of meta, used to cover or shield the upper edges of
the membrane base flashing, wall flashing or primary flashing.
(see Flashing and Coating)
Cap Sheet: a granule-surface coated sheet used as the top ply of some built-up or
modified bitumen roof membranes and/or flashing.
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.
Chalking: the degradation or migration of an ingredient, in paints, coatings or other
Coated Base Sheet: a felt that has previously been saturated (impregnated) with
asphalt and later coated with harder, more viscous asphalt,
which greatly increases its impermeability to moisture.
Coated Felt (sheet): (1) an asphalt-saturated felt that has also been coated on both
sides with harder, more viscous “coating” asphalt; (2) a glass fiber
that has simultaneously impregnated and coated with asphalt on
Cold Process Built-Up Roof: a continuous, semi-flexible roof membrane, consisting
of a ply or plies of felts, mats or other reinforcement
fabrics that are laminated together with alternate layers
of liquid-applied(usually asphalt-solvent based) roof
cement or adhesives installed at ambient or a slightly
Condensation: the conversion of water vapor or other gas to liquid state as the
Temperature drops or atmospheric pressure rises. (Also see Dew Point)
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: formed metal sheeting secured on or into a wall, curb, pipe, roof-
top unit or other surface, to cover and protect the upper edge of the
membrane base flashing or underlying metal flashing and associated
fasteners from exposure to the weather.
Course: (1) the term used for each row of shingles of roofing material that forms the
roofing, waterproofing or flashing system: (2) one layer of a series of material
applied to a surface (e.g. a five-course wall flashing is composed of three
applications of roof cement with one ply of felt or fabric sandwiched between
each layer of roof cement)
Coverage: the surface area covered by a specific quantity of a particular material.
Cricket: an elevated roof substrate or structure, constructed to divert water around a
chimney, curb, away from a wall, expansion joint or other projection/pene-
tration. (See Saddle)
Curb: (1) a raised member used to support roof penetrations, such as skylights,
mechanical equipment, hatches, ect., above the level of the roof surface; (2)
a raised roof perimeter relatively low in height.
Deck: a structural component of the roof of a building. The deck must be capable of
safely supporting the design dead and live loads, including the weight of the
roof systems, and the additional live loads required by the governing building
codes. Decks are either non-combustible(e.g., corrugated metal, concrete or
gypsum) or combustible(e.g., wood plank or plywood), and provide the substance
to which the roofing or waterproofing system is applied.
Deflection (Bowing, Sagging): the download displacement of a structural member
or system under load.
Degradation: a deleterious change in the chemical structure, physical properties or
appearance of a material due to natural or artifical exposure(e.g.,
exposure to radiation, moisture, heat, freezing, wind, ozone, oxygen, ect.)
Delamination: a separation of the laminated layers of a component or system.
Drain: an outlet or other device used to collect and direct the flow of runoff water
from a roof area. (See NRCA Construction Detail “W-1”.)
Drip Edge: a metal flashing or other overhanging component, with an outward pro-
jecting lower edge, intended to control the direction of dripping water and
help protect underlying building components. A drip edge also can be used
to break the continuity of contact between the roof perimeter and wall com-
ponents to help prevent capillary action.
Eave: a projecting edge of a roof that extends beyond the supporting wall.
Efflorescence: the formulation of crystalline deposits, generally whitish in color, on the
surface of stone, brick, concrete or other masonry surface when moisture
moves through and evaporates on the masonry. May also be caused by
free alkalies leached from mortar, grout or adjacent concrete.
Elastomeric: the elastic, rubber-like properties of a material that will stretch when
pulled and will return relatively quickly to its original shape when
End Lap: the distance of overlap where one ply, panel or piece extends beyond the
end of the immediately adjacent underlying ply, panel or piece.
EPDM: Ethylene Propylene Diene Monomer (See also Ethylene Propylene Diene
Exhaust Ventilation: air that is typically vented or exhausted from the roof cavity,
typically through vents installed on the upslope portion of the
roof. For example, with most steep-slope roof assemblies
exhaust vents are typically located at or near the ridge.
Expansion Joint: a structural separation between two building elements that allows
free movement between the elements without damage to the roofing
Fabric: a woven cloth or material of organic or inorganic filaments, threads or yarns
used for reinforcement in certain membranes and flashings
Fascia: a vertical of steeply sloped roof or tim located at the perimeter of a building.
Typically it is a border for the low-slope roof system the waterproofs the
interior portions of the building.
Fasteners: any of a wide variety of mechanical securement devices and assemblies,
including nails, screws, cleats, clips, and bolts, which may be used to
to secure various components of a roof assembly.
Felt: a flexible sheet manufactured by the interlocking of fibers through a combina-
tion of mechanical work, moisture and heat. Roofing felts may be manufactured
principally from wood pulp and vegetable fibers ( organic felts), asbestos fibers
(asbestos felt), glass fibers(fiberglass or plysheet) or polyester fibers.
Field of the Roof: the central or main portion of a roof, excluding the perimeter and
Field Seam: a splice or seam made in the field (not factory) where overlapping sheets
are joined together using an adhesive, splicing tape or heat- or
Fishmouth: (also referred to as an edge wrinkle): (1) a half-cylindrical or half-conical
shaped opening or void in a lapped edge or seam, usually caused by
wrinkling or shifting of plysheets during installation; (2) in shingles, a half-
conical opening formed at a edge.
Flange: the projecting edge of a ridge or semi-rigid component, such as a metal edge
flashing flange, skylight flange, flashing boot, structural member, ect.
Flashing: components used to weatherproof or seal the roof system edges at perime-
ters, penetrations, walls, expansion joints, valley drains, and other places
where the roof covering is interrupted or terminated. For example, membrane
base flashing covers the edge of the field membrane, and cap flashings or
counterflashings shield the upper edges of the base flashing.
Gable: a triangular portion of the endwall of a building directly under the slope roof
and above the eave line.
Gable-shaped Roof: a single-ridge roof that terminates at gable end(s).
Galvanized Steel: steel coated with zinc for corrosion resistence.
Gauge: a measurement of metal thickness.
Glass Felt: a sheet composed of a bonded glass fibers, suitable for impregnation and
coating in the manufacture of bituminous roofing and waterproofing
materials and shingles.
Granule: (also referred to as a mineral or ceramic granule): opaque, natural, or
synthetically colored aggregate commonly used to surface cap sheets,
shingles, and other granule-surfaced roof coverings.
Heat Welding: (see heat seaming): method of melting and fusing together the
overlapping edges of separate sections of thermoplastic or
elastomeric roofing membranes by the application of heat(in the
form of hot-air or open flame) and pressure.
Hip: the inclined external angle formed by the intersection of two sloping roof planes.
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 maximum
amount that the air could contain at the same temperature.)
HVAC: heating, ventilating, and air conditioning equipment.
Inorganic: any chemical or compound that is derived from minerals, does not
contain carbon, and is not classified as organic; being or composed
of materials other than hydrocarbons and their derivatives; not of plant
or animal origin.
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.
Lap: that a part of a roofing, waterproofing or flashing component that overlaps or
covers any portion of the same or another type of adjacent component.
Lap Seam: occurs where overlapping materials are seamed, sealed or otherwise bonded.
Lead: a soft workable metal used for miscellaneous flashings.
Life Cycling Costing: a method of economic analysis that takes into account
expected costs over the useful life of an asset.
Mansard: a decorative steep sloped roof on the perimeter of the building.
Mansard Roof: a steeper roof that terminates into a flat roof at its high point.
Mat: a thin layer of woven, non-woven or knitted fiber that serves as reinforcement
to the material or membrane.
Material Safety Data Sheets: a written description of the chemicals within a product,
and pertinent other 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 employer’s responsibility
to communicate its contents to employees.
Mechanically-Fastened Membranes: generally used to describe membranes that have
been attached at defined intervals to the substrate.
Mechanical fastening maybe performed with
various fasteners and/or mechanical devices, such
as plates or battens.
MIL: a unit of measure, one mil is equal to 0.001 inches or 25.400 microns, often used,
to indicate the thickness of a roofing membrane.
Mineral-Surfaced Roofing: roofing materials whose surface or top layer consists of
Mineral-Surfaced Sheet: a roofing sheet that is coating on one or both sides with
asphalt and surfaced with mineral granules.
Modified Bitumen: (1) a bitumen modified through the inclusion of one or more
polymers (e.g. atactic polypropylene, styrene butadiene, ect.)
(2) composite sheets consisting of a polymer modified bitumen
often reinforced and sometimes surfaced with various types of mats,
films, foils and mineral granules.
Moisture Scan: the use of a mechanical device (capitance, infrared or nuclear) to detect
the presence of moisture within a roof assembly. (See Non-Destructive
Mopping: the application of hot bitumen, with a roofer’s hand mop or mechanical
applicator, to the substrate or to the felts of a bituminous membrane.
Types of Mopping:
(A) Solid: a continuous mopping of a surface.
(B) Spot: a mopping pattern in which hot bitumen is applied in roughly circular areas,
leaving a grid of unmapped, perpendicular bands on the roof.
(C) Sprinkle: a random mopping pattern in which heated bitumen beads are strewn onto the
substrate with a brush or mop.
(D) Strip: a mopping pattern in which hot bitumen is applied in parallel bands.
Mud Cracking: surface cracking of a material whereby the degraded material appears
similar to dried, cracked earthen mud.
Net Free Vent Area: the area, measured in square inches, open to “unrestricted” air
flow and commonly used as a “yardstick” to measure relative
NRCA: National Roofing Contractors Association
Organic: being or composed of hydrocarbons or their derivatives originating from plant
or animal matter.
Penetration: (1) any object passing through the roof; (2) the consistency(hardness) of a
bituminous material expressed as the distance, in tenths of a millimeter
(0.1mm), that a standard needle penetrates vertically into a sample of
material under specified conditions of loading, time, and temperature.
Permeance: the rate of water vapor transmission per unit area at a steady state through
a material, membrane or assembly, expressed in Grain/Square Foot Hour
Inch Mercury (grain/ft_h in Hg [ng/Pa a m_]).
Phased Application: the installation of separation roof system or waterproofing system
component(s) during two or more separate time intervals.
Application of surfacings at different time intervals are typically
not considered phased application. (See Surfacing.)
Picture Framing: a square or rectangular pattern of buckles or ridges in a roof covering
generally coinciding with insulation or deck joints; generally, a
function of movement of the substrate.
Plastic Cement: a roofing industry generic term used to describe Type I asphalt roof
cement that is a trowelable mixture of solvent-based bitumen, mineral
stabilizers, other fibers and/or fillers. Generally, intended for use on
relatively low slopes-not vertical surfaces. (Also see Asphalt Roof
Cement and Flashing Cement.)
Ply: a layer of felt, plysheet or reinforcement in a roof membrane or roof system.
Polyester: a thermoplastic polymeric resin that is used to make a variety of materials
and products. Polyester fibers are widely used as the reinforcing medium
in certain membranes.
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.
PVC: Polyvinyl Chloride
Rake: the slope edge of a roof at or adjacent to the first or last rafter.
RCI: Roof Consultants Institute
Re-Cover: the addition of a new roof membrane or steep slope roof covering over a
major portion of an existing roof assembly. This process does not involve
removal of the existing roofing.
Reroofing: the process of re-covering or tearing-off and replacing an existing roof
Reglet: a sheet metal receiver for the attachment of counterflashing. (A reglet
may be insert into a raggle, embedded behind cladding or be surface mounted.)
Reflective Humidity: the ratio of the weight of moisture in a given volume of air-
vapor mixture to the saturated (maximum) weight of water vapor
at the same temperature, expressed as a percentage. For example,
if the weight of the moist air is 1 pound and if the air could hold 2
pounds of water vapor at the temperature, relative humidity(RH)
is 50 percent.
Replacement: the practice of removing an existing roof system down to the roof deck
and replacing it with a new roofing system.
Ridge: highest point on the roof, represented by a horizontal line where two roof areas
Intersect, running the length of the area.
Ridge Vent: one of many products located at the ridge that allows the escape of warm
and/or moist air from the attic area or rafter cavity. Most ridge vents are
either premanufactured metal or flexible shingle over.
Roof Curb: raised frame used to mount mechanical units(such as air conditioning or
exhaust fans), skylights, ect.
Roof Jack: a metal bracket used to support toe-boards on steep-slope roofs.
Roof Overhang: a roof extension beyond the exterior wall of a building.
Roof Slope: the angle a roof surface makes with the horizontal, expressed as a
ration of the units of vertical rise to the units of horizontal length
(sometimes referred to as run). For English units of measurements,
when dimensions are in inches,slope may be expressed as a ratio of
rise of run, such as 4:12 or as a percent.)
Roof System: a system of interacting roof components, generally consisting of
membrane or primary roof covering and insulation (not including
the roof deck) designed to weatherproof and, sometimes to improve
the building’s thermal resistance.
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 based. (See Cricket)
SBS: (See Styrene Butadience Styrene.)
Sealant: a single – or multi-component polymeric or bituminous-based material used
to weatherproof many types of construction joints where moderate movement
is expected. The material comes in various grades: pourable, self-leveling,
non-sag, gungrade, and cured or uncured tapes.
Seam: a joint formed by mating two separate sections of materials. Seams may be made
or sealed in a variety of ways, including adhesive bonding, hot-air welding,
solvent welding, using adhesive tape, sealant, ect.
Selvage Edge: an edge designed for certain sheet good materials, e.g., mineral-sur-
faced sheets. With mineral surfaced sheets, the surfacing is omitted over
a portion of longitudinal edge of the sheet (e.g., mineral surface cap
sheet) in order to obtain better adhesion of the overlapping sheet.
Side Lap: the continuous longitudinal overlap of neighboring like materials.
Single-Ply Membranes: roofing membranes that are field applied using just one layer
of membrane material (either homogeneous or composite)
rather than multiple layers.
Single-Ply Roofing: a roofing system in which the principal roof covering is a single
layer flexible membrane, often of thermoset, thermoplastic or
polymer modified bituminous.
Skylight: a roof accessory, set over an opening in the roof, designed to admit light.
Normally transparent, and mounted on a raised framed curb.
Slip Sheet: sheet material, such a reinforced kraft paper, rosin-sized paper, polyester
scrim or polyethylene sheeting, placed between two components of a roof
assembly (such as between membrane and insulation or deck) to ensure that
no adhesion occurs between them, and to prevent possible damage from
chemical incompatibility, wearing or abrasion to the membrane.
Smooth Surfaced Roof: a roof membrane without mineral granule or aggregate
Soil Stack: a sanitation pipe that penetrates the roof; used to vent plumbing fixtures.
Solvent: liquid used to dissolve or disperse film-forming constituents, and which
evaporates during drying and does not become a part of the dried film.
Split: a rupture (generally linear) or tear in a material or membrane resulting from
Square: 100 square feet (9.29 m ) of roof area.
Standing Seam: a metal roof system that consists of an overlapping or interlocking
seam that occurs at an upturned rib. The standing seam may be made
by turning up the edges of two adjacent metal panels and overlapping
them, then folding or interlocking them in a variety of ways.
Substrate: the surface upon which the roofing or waterproofing membrane is applied
(e.g., in roofing, structural deck or insulation).
Sump: an intentional depression around a roof drain or scupper that serves to promote
Surfacing: the top layers of a roof covering, specified or designed to protect the under-
lying, roofing from direct exposure to the weather.
Test Cut: a sample of the roof, which may contain all components or just the membrane,
usually used to diagnose the condition of the existing membrane, evaluate the
type and number of piles or number of membranes or rates of application such
as determine the weight of the average interply bitumen moppings.
Thermal Shock: the stress-producing phenomenon resulting from sudden temperature
changes in a roof membrane when, for example, a cold rain shower
follows brilliant hot sunshine, which may result in sudden cooling or
rapid contraction of the membrane.
Thermoplastic: materials that soften when heated and harden when cooled. This
process can be repeated provided that 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
UL: Underwriters Laboratories, Inc.
UN Label: an identification label or seal affixed to a roofing product or package with
the authorization of Underwriters Laboratories, Inc. The presence of the
label indicates that the product has met certain performance criteria.
Underlayment: an asphalt-saturated felt or other sheet material (may be self-adhering)
installed between the roof deck and the roof system, usually used in a
steep-slope roof construction. Underlayment is primarily used to
separate the roof covering from the roof deck, to shed water, and to
provide secondary weather protection for the roof area of the building.
Valley: the internal angle formed by the intersection of two sloping roof planes.
Vent: an opening designed to convey air, heat, water vapor or other gas from inside
a building or building component to the atmosphere.
Void: an open space or break in consistency.
Waterproof: the quality of a membrane, membrane material or other component to
prevent water entry.
Wind Uplift: the force caused by the deflection of wind at roof edges, roof peaks or
obstructions, causing a drop in air pressure immediately above the roof
surface. This force is then transmitted to the roof surface. Uplift may
occur because of the introduction of air pressure underneath the membrane
and roof edges, where it can cause the membrane to balloon and pull away
from the deck.