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ALLIGATORING
Shrinkage cracking of the bituminous surface of built-up roofing, or the exposed surface of the smooth surfaced roofing, in which the loss of volatile oils under solar radiation produces a pattern of deep cracks with the scaly look of an alligator's hide.

ASPHALT
A dark brown to black, highly viscous hydrocarbon found in natural deposits or produced from the residuum left after the distillation of petroleum used as the waterproofing agent of a built-up roof. It comes in a wide range of viscosities and softening points - from about 135F (dead level asphalt) to 210F or more (steep asphalt). (see Bitumen)

BACKNAILING
The practice of blind nailing in addition to mopping all the plies to a substrate to prevent slippage on slopes of 1 ½" or more for steep asphalt, ½" or more for coal tar pitch and dead level asphalt.

BASE SHEET
A saturated or coated felt placed as the first ply in a multi-ply built-up roofing membrane.

BITUMEN
The generic term for an amorphous, semi-solid mixture of complex hydrocarbons derived from petroleum or coal. In the roofing industry there are two basic bitumens; asphalt and coal tar pitch. Before application they are either (1) heated to a liquid state, (2) dissolved in a solvent, or (3) emulsified.

BLEEDING
The action of an undercoating of paint that seeps through the top coating.

BLISTER
A spongy, raised portion of a roofing membrane - ranging in size from 1" in diameter and barely detectable height, to as much as 50 sq. ft. in area and 1 ft. high. Blisters result from the pressure of moisture that expands as it is vaporized by the sun's heat.

BOND
Adhesive strength preventing delamination of two roofing components. (see also Manufacturer's Bond)

BTU (BRITISH THERMAL UNIT)
The heat energy required to raise 1 lb. of water 1F in temperature.

BUILT-UP ROOFING MEMBRANE
A continuous, semi-flexible roof covering of laminations, or plies, of saturated or coated felts alternated with layers of bitumen, surfaced with mineral aggregate or asphaltic materials.

BUR
Abbreviation sometimes used for built-up roofing membrane.

CANT STRIP
A continuous strip of triangular cross section, fitted into the angle formed by a structural deck and a wall or other vertical surface. The 45 slope of the exposed surface of the cant strip provides a gradual transition for the base flashing and roofing membrane from a horizontal roof surface to a vertical surface.

CAP FLASHING
(see Flashing)

CAP SHEET
A fiberglass or felt membrane used with asphaltic materials to completely recover an existing roof.

COAL TAR PITCH
Dark brown to black solid hydrocarbon obtained from the residuum of the distillation of coke oven tar, used as the water-proofing agent of dead level or low slope built-up roofs. It comes in a narrow range of softening points - from 140F to 155F. Hot coal tar pitch tends to be very brittle and easily cracked by building movement in cold weather.

COATED BASE SHEET (OR FELT)
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.

COLD PROCESS ROOFING
A bituminous membrane comprising layers of coated felts or fiber glass bonded with cold applied asphalt adhesive and surfaced with a cutback or emulsified asphalt roof coating. Also applies to solvent reduced coal tar pitch.

CONDENSATION
The process through which water vapor (a gas) liquefies as air temperature drops or atmospheric pressure rises. (see Dew Point)

COPING
The top part of a parapet or firewall, metal, tile or other cementitious material.

CORRUGATED ROOF
Any type of metal roof covering that has corrugations, formed by rolling the metal into a series of arcs or valleys and ridges for increased strength.

COUNTERFLASHING
(see Flashing)

COVERAGE
The surface area in squares (100 square feet) that should be continuously coated by a specific unit of a roofing materials, after allowance is made for a specified lap.

CRACK
A membrane tear produced by bending, often wrinkle.

CREEP
(1) Permanent elongation or shrinkage of the membrane resulting from thermal or moisture changes; (2) permanent deflection of structural framing or structural deck resulting from plastic flow under continued stress or dimensional changes accompanying changing moisture content or temperature.

CUTBACK
An organic, solvent thinned, soft or fluid cold process bituminous roofing coating or flashing cement. May be asphalt or coal tar pitch base.

CUTOFF
A detail designed to prevent lateral water infiltration into the insulation where it terminates at the end of the day's work. A felt strip is (normally) hot mopped to the stepped contour of the deck, the insulation edge, and the horizontal insulation surface.

DADO
A rectangular groove cut across the grain of a wood blocking member, normally to provide edge canting at the periphery of a roof.

DEAD LEVEL
Absolutely horizontal, of zero slope. (see Slope)

DECK
The structural top of a building upon which is laid the insulation and the BUR. May be steel, concrete, gypsum, Zonolite or other structural material.

DELAMINATION
A built-up roofing membrane failure characterized by separation of the felt plies, sometimes resulting in wrinkling and cracking.

DEW POINT
The temperature at which water vapor starts to condense in cooling air, with no change in atmospheric pressure or vapor content.

EAVE
The low side of a roof extending out over the walls.

EDGE STRIPPING
Application of felt strips cut to narrower widths than the normal 36" felt roll width to start the felt shingling pattern at a roof edge.

EDGE VENTING
The practice of providing regularly spaced openings at a roof perimeter to relieve the pressure of water vapor entrapped in the insulation.

ELASTOMERIC
Having elastic properties, capable of expanding or contracting with the surfaces to which the material is applied without rupturing.

EMULSION
An intimate mixture of bitumen and water, with uniform dispersion of the bitumen globules achieved through a chemical or clay emulsifying agent.

ENVELOPE
The continuous edge formed by folding an edge base felt over the plies above and securing it to the top felt, or if above - deck insulation is used to the top surface of the insulation. The envelope thus prevents bitumen drippage through the exposed edge joints of the laminated, built-up roofing membrane and also prevents lateral water infiltration into the insulation.

EQUILIBRIUM MOISTURE CONTENT
The moisture content, expressed as percentage of moisture weight to material weight, at a given temperature and relative humidity.

EXPANSION / CONTRACTION
The spreading or shrinking of surfaces due to changing temperatures. Hot weather causes expansion, while cold weather causes contraction or shrinking.

EXPOSURE
The transverse dimension of a felt not overlapped by an adjacent felt in a built-up roofing membrane. The exposure is thus that part of the felt covered directly by the flood top coat. The correct felt exposure in a shingled, multi-ply roof is computed by dividing the felt width minus 2" by the number of plies (e.g., for two plies of 36" wide felt, the exposure equals 36 - 2/2 or 17".)

FALLBACK
A reduction of bitumen softening point, sometimes caused by mixing live asphalt with live coal tar pitch or over heating the bitumen. (see Softening Point Drift)

FELT
A fabric manufactured by the interlocking of fibers through a combination of mechanical work, moisture, and heat, without spinning, weaving, or knitting. Roofing felts are manufactured from vegetable fibers (organic felts), or glass fibers (glass fibered felts).

FIRE WALL
A non-combustible wall that separates various parts of a building to prevent the spread of fire.

FISHMOUTH
An opening formed by an edge wrinkle in a felt where it overlaps another felt in a built-up roofing membrane.

FLASHING
Connecting devices that seal membrane joints at expansion joints, drains, gravel stops, and other places where the membrane is interrupted. Base Flashing forms the upturned edges of the water tight membrane. Cap or Counterflashing shields the exposed edges and joints of the base flashing.

FLASHING CEMENT
A trowelable plastic mixture of bitumen and other inorganic reinforcing fibers and a solvent.

FLOOD COAT
The top layer of bitumen in an aggregate surface, built-up roofing membrane. Correctly applied, it is poured not mopped - to a weight of 60 lbs. per square for asphalt, 75 lbs. per square for coal tar pitch.

GAMBREL ROOF
A roof with two separate degrees of pitch on each side of the ridge. The lower side of the roof has a much steeper pitch than the upper part.

GLAZE COAT
(1) The top layer of asphalt in a smooth surfaced built-up roof assembly; (2) a thin protective coating of bitumen applied to the lower plies or top of a built-up membrane, when the top pouring and aggregate surfacing are delayed. (see Phased Application).

GRAIN
Weight unit equal to 1/7,000 lbs., used in measuring atmospheric moisture content.

GRAVEL
Coarse, granular aggregate, with pieces larger than sand grains, resulting from the natural erosion or crushing of rock.

GRAVEL STOP
Flanged device, normally metallic, designed to prevent loose aggregate from washing off the roof and to provide a finished edge detail for the built-up roofing assembly.

HOT STUFF OR HOT
Roofer's term for hot bitumen. May be asphalt or coal tar pitch.

HYPALON
A synthetic rubber (chemically chlorosulfonated polyethylene) often used in conjunction with neoprene in elastomeric roof coverings. (Hypalon is a registered trademark of E.I. du Pont de Nemours &' Company).

INSULATION
A material applied to retard the flow of heat through an enclosing surface. For roofs it should have a maximum thermal conductance (C value) of 0.5 (BTU) (hr)/ (sq. ft.) (F)

MEMBRANE
A flexible or semi-flexible roof covering, used in conjunction with hot or cold bitumen or reinforced BUR systems. May be organic, fiberglass or polyester.

MINERAL GRANULES
Natural or synthetic aggregate ranging in size from 500 microns to 1/4" diameter, used to surface cap sheets, slate sheets, and shingles. They are designed to face the weather without any further coating.

MINERAL SURFACED SHEET
An asphalt saturated felt, coated on one or both sides and surfaced on the weather exposed side with mineral granules, usually 90 lbs. per square.

MOPPING
A hot application of bitumen with a mop or mechanical applicator to the substrate or to the felts of a built-up roofing membrane. (1) Solid Mopping: A continuous mopping of the surface with no unmopped areas. (2) Spot Mopping: A mopping pattern in which the hot bitumen is applied in roughly circular areas, generally about 18" in diameter, with a grid of unmopped perpendicular bands. (3) Strip Mopping: A mopping pattern in which the hot bitumen is applied in parallel bands, generally 8" wide with unmopped spaces. (4) Sprinkle Mopping: A random pattern of heated bitumen beads hurled onto the substrate from a broom or mop.

NEOPRENE
A synthetic rubber (chemically polychloroprene) used in fluid or sheet applied elastomeric roofing membranes or flashing.

NON-FIBERED
Refers to roof coating that does not contain reinforcing fibers (as opposed to fibrated coatings), and to roofing primer, which does not contain reinforcing fiber.

OXIDATION
The forming of an oxide. The process where by material combines with free oxygen in the air.

PARAPET WALL
That part of the building's outside walls extending above the roof.

PERLITE
An aggregate used in lightweight insulating concrete decks and in preformed insulating board, formed by heating and expanding silicaceous volcanic glass.

PERM
A unit of water vapor transmission, defined as 1 grain of water vapor per square foot per hour per inch of mercury pressure difference (1" Hg equals 0.491 psi).

PERMEANCE
An index of a material's resistance to water vapor transmission. (see Perm)

PHASED APPLICATION
The practice of applying the felt plies of a built-up roofing membrane in two or more operations, separated by a delay normally of at least 1 day.

PITCH
(see Slope)

PITCH POCKET
A flanged metal container placed around a column or other roof penetrating element and filled with bitumen or flashing cement to seal the joint.

PLASTIC CEMENT
(see Flashing Cement)

PLY
A layer of felt in a built-up roofing membrane. A four ply membrane has at least four plies of felt at any vertical cross section cut through the membrane. The dimension of the exposed surface (exposure) of any ply may be computed by dividing the felt width minus 2" by the number of plies; thus, the exposed surface of a 36" wide felt in a four ply membrane should be 8 ½". (see Exposure)

PRIMER
A thin liquid cutback bitumen applied to a surface to resaturate existing felts and to improve the adhesion of heavier applications of bitumen.

RAKE ANGLE
The part of a roof at its intersection with a gable.

REGLET (or Cap Flashing)
A groove in a wall or other vertical surface metal adjoining a roof surface for the embedment of counterflashing.

RELATIVE HUMIDITY
The ratio of the weight (or partial pressure) of water vapor actually diffused through an air vapor mixture to the saturated weight (or partial pressure) of the water vapor.

RIDGE
Mounds on the roof caused by wind action pushing poorly adhered felts out of place.

RISE:
(see Slope)

ROLL ROOFING
Coated felts, either smooth or mineral surfaced.

ROOF MAT
That part of a BUR on top and exclusive of the deck or insulation.

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

TAB
The exposed portion of strip shingles by cutouts.

TAPERED EDGE STRIP
A tapered insulation strip used to (1) elevate the roof at the perimeter and at curbs that extend through the roof and (2) provide a gradual transition from one layer of insulation to another.

TAPERED INSULATION
A system of precut or pre-molded insulation boards or a poured insulation fill designed to provide slope to the roof deck before installing the roof membrane.

TAPING
The technique of taping joints between insulation boards on deck panels. (See STRIPPING)

TAR
A brown or black bituminous material, liquid or semisolid in consistency, in which the predominating constituents are bitumens obtained as condensates in the processing of coal, petroleum, oil-shale, wood or other organic materials; also found in nature.

TAR BOILS
Bubbles of moisture vapor encased in a thin film of bitumen, also known as blueberry, blackberry, etc.

TARRED FELTS
A felt that has been saturated with a refined coal tar.

TEAR OFF - ASTM
To remove an existing roof down to the structural deck.

TEDLAR:
Polyvinyl fluoride, used as a film surfacing in elastomeric membranes. (Tediar is a registered trademark of E.I. du Pont de Nemours & Company).

TERMINATION
The treatment or method of anchoring the free edges of the membrane in a roofing system.

TERRACOTTA TILE
Brownish-orange unglazed roof tiles.

TEST CUT
A sample of the roof membrane, usually 4 inches by 40 inches in size, that is cut from a roof membrane to determine the weight of the average interply bitumen poundages, diagnosing the condition of the existing membrane (e.g., to detect leaks or blisters).

TEXTURAL
Description of slate shingle placement or pattern method.

THERMAL CONDUCTANCE (C)
A unit of heat flow that is used for specific thickness of material or for materials or combination construction, such as laminated insulation.

THERMAL CONDUCTIVITY (K)
Heat energy in BTU per hour transferred through a 1" thick 1 square foot area of homogeneous material per F of temperature difference from surface to surface.

THERMAL IMAGE
A visual representation of temperature distribution over a surface area. An image on a television-like display presenting the response to infrared light waves.

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

THERMAL LEVEL CONTROL
The position in the temperature range where the thermal range is located.

THERMAL RESISTANCE (R)
An index of a material's resistance to heat transmission, the reciprocal of thermal conductivity (K) or thermal conductance (C).

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

THERMAL STRESS
The effect when the expansion from heat or contraction from cold is applied.

THF
Tetrahydrofuran; solvent used to chemically weld laps of some thermoplastics and uncured elastometers.

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

TIN CAP
A metal disk approximately 2" in diameter and not less than 32 gauge used with a fastener driven through it for the attachment of underlayment or an anchor sheet for built-up-roofing.

TONGUE & GROOVE PLANKS
One of the oldest types of structural roof decking. The sides are cut with a convex or concave groove so adjacent planks may connect to each other to form a monolithic wood system. Tongue and groove wood planks are typically used where the wood roof decking is exposed.

VALLEY
Formed by the lower meeting of two roof slopes.

VAPOR BARRIER
A material designed to restrict the passage of water vapor through a wall or roof. In the roofing industry, it should be rated at 0.2 perm or less.

VAPOR MIGRATION
The movement of water vapor molecules from a region of high vapor pressure to a region of lower vapor pressure, penetrating building roofs and walls.

VENT
A stack designed to convey water vapor or other gas from inside a building or a building component to the atmosphere.

VERMICULITE
An aggregate used in lightweight insulating concrete, formed by heating and consequent expansion of mica rock.

WEATHERING
The aging effects caused by heat, light, temperature, and atmospheric air which determine the life span of the coating.
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