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Standard Definitions of Roofing Terms

Get familiar with common roofing terminology and jargon that can help you understand the industry more clearly.

aggregate – (1) crushed stone, water-worn gravel used for built-up roof; crushed slag, or for surfacing; (2) any granular mineral material

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 not end through the surfacing bitumen

application rate – the quantity (mass, volume, or thickness) of material applied per unit area

asbestos – a group of natural fibrous impure silicate materials

asphalt – a dark brown to black cementitious material in which the predominating constituents are bitumens which occur in nature or are obtained in petroleum processing

asphalt, air is blown – an asphalt produced by blowing air through molten asphalt at an elevated temperature to raise its softening point and modify other properties

asphaltene – a high molecular weight hydrocarbon fraction precipitated from asphalt by a designated paraffinic naphtha solvent at a specified temperature and solvent asphalt ratio. (The asphaltene fraction should be identified by the temperature and solvent ratio used)

asphalt mastic – a mixture of asphaltic material and graded mineral aggregate that can be poured when heated, but requires mechanical manipulation to apply

asphalt rock (rock asphalt) – a naturally occurring rock formation, usually limestone or sandstone, containing throughout its mass a minor amount of asphalt

back nailing – the practice of blind-nailing roofing felts to a substrate in addition to hot-mopping to prevent slippage

base ply – the bottom or first ply in a built-up roofing membrane when additional plies are to be subsequently installed

base sheet – a product intended to be used as a base ply in a built-up roofing system

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 asphalts, tars, pitches, and asphaltites; (2) a generic term used to denote any material composed principally of bitumen

bitumenized, adj. – impregnated with bitumen Example: bituminized fiber pipe

bituminous emulsion – a suspension of minute globules of bituminous material in water or in an aqueous solution

bituminous grout – a mixture of bituminous material and fine sand that will flow into place without mechanical manipulation when heated

blast-furnace slag – the non-metallic product, consisting essentially of silicates and alumino-silicates of calcium and other bases, that is developed in a molten condition simultaneously with iron in a blast furnace

blind nailing – the use of nails that are not exposed to the weather in the finished roofing

blister – (1) a raised portion of a roofing membrane resulting from local internal pressure; (2) the similarity fom1ed protuberances in coated prepared roofing

blocking – (1) wood built into a roofing system above the deck and below the membrane and flashing to (a) stiffen the deck around an opening, (b) act as a stop for insulation, (c) serve as a nailer for attachment of the membrane or flashing; (2) wood cross-members installed between rafters or joists to provide support at cross-joints between deck panels; (3) cohesion or adhesion between similar or dissimilar materials in roll or sheet fom1 that may interfere with the satisfactory and efficient use of the material

bond – the adhesive and cohesive forces holding two roofing components in intimate contact

brooming – embedding a ply by using a broom to smooth it out and ensure contact with the adhesive under the ply

built-up roofing – a continuous, semiflexible membrane consisting of plies of saturated felts, coated felts, fabrics, or mats assembled in place with alternate layers of bitumen, and surfaced with mineral aggregate, bituminous materials, or a granule surfaced sheet (abbreviation, B.U.R)

cant strip – a beveled strip used under flashings to modify the angle at the point where the roofing or waterproofing membrane meets any vertical element

cap flashing – See flashing

cap sheet – a granule-surfaced coated felt used as the top ply of a built-up roofing membrane

cationic emulsion – an emulsion in which the emulsifying system establishes a predominance of positive charges on the discontinuous phase

caulking – a composition of vehicle and pigment, used at ambient temperatures for filling joints, that remains plastic for an extended time after application

channel mopping – See mopping, (3) strip

coal tar – a dark brown to black, solid cementitious material obtained as a residue in the partial evaporation or distillation of coal tar

coal-tar felt – a felt that has been saturated with refined coal tar

coal-tar pitch – a dark brown to black, solid cementitious material obtained as a residue in the partial evaporation or distillation of coal tar

coated sheet (or felt) – (1) an asphalt felt that has been coated on both sides with harder, more viscous asphalt; (2) a glass fiber felt that has been simultaneously impregnated and coated with asphalt on both sides

coke-oven tar – See coal tar

cold-process roofing – a continuous, semiflexible membrane consisting of plies of felts, mats, or fabrics laminated on a roof with alternate layers of roof cement and surfaced with a cold-applied coating

condensation – the conversion of water vapor or other gas to liquid as the temperature drops or atmospheric pressures rise; (see also dew point)

conductance, thermal – the thermal transmission in unit time through a unit area of a particular body or assembly having defined surfaces, when the unit average temperature difference is established between the surfaces. C = W/m2 * K (C = Btu/h * FT2 * 0F).

conductivity, thermal – the thermal transmission, by conduction only, in unit time through the unit area between two isothermal surfaces of an infinite slab of a homogeneous material of unit thickness, in a direction perpendicular to the surface, when the unit temperature difference is established between the surfaces. k = WIm * K (k = Btu * In./h * ft2 * 0F).

cone penetration – See penetration

coping – a covering on top of a wall exposed to the weather, usually sloped to carry off water

counterflashing – formed metal or elastomeric sheeting secured on or into a wall, curb, pipe, roof-top unit, or other surfaces, to cover and protect the upper edge of a base flashing and its associated fasteners

coverage – the surface area to be continuously covered by a specific quantity of a particular material

creep – the time-dependent part of a strain resulting from stress

cricket – a relatively small, elevated area of a roof constructed to divert water from a horizontal intersection of the roof with a chimney, wall, expansion joint, or other projection

crushed stone – tile product resulting from the artificial crushing of rocks, boulders, or large cobblestones, substantially all faces of which have resulted from the crushing operation

dampproofing – treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure

dead level – absolutely horizontal or zero slopes (see a/so slope)

dead level asphalt – a roofing asphalt conforming to the requirements of Specification D312, Type 1

dead level roofing – a roofing system applied on a surface with a 0 to 2% incline

deck – the structural surface to which the roofing or waterproofing system (including insulation) is applied

direction change – a change in the orientation of the principal dimension or of the support of adjoining units of the roofing system

double pour – apply two layers of aggregate and bitumen to a built-up roof

dry felt – (1) see felt; (2) a felt which has not been saturated with bitumen

edge stripping – application of felt strips cut to narrower widths than the normal felt-roll width to cover a joint between flashing and built-up roofing

edge venting – the practice of providing regularly spaced protected openings at a roof perimeter to relieve water vapor pressure in the insulation

elastomer – a macromolecular material that returns rapidly to its approximate initial dimensions and shape after substantial deformation by a weak stress and subsequent release of that stress

embedment – (1) the process of pressing a felt, aggregate, fabric, mat, or panel uniformly and completely into hot bitumen or adhesive to ensure intimate contact at all points; (2) the process of pressing granules into coating in the manufacture of factory prepared roofing, such as shingles

emulsion – an intimate mixture of bitumen and water, with a uniform dispersion of tile bitumen or water globules, usually stabilized by an emulsifying agent or system

envelope – a continuous membrane edge seal fonned at the tile perimeter and penetrations by folding the base sheet or ply over the plies above and securing it to the top of the membrane. The envelope prevents bitumen seepage from the edge of the membrane.

equilibrium moisture content – (1) the moisture content of a material stabilized at a given temperature and relative humidity, expressed as percent moisture by weight; (2) the typical moisture content of a material in any given geographical area

equiviscous temperature (EVT) – the temperature at which the viscosity of asphalt is 125 nun2!s (125 CST); the recommended asphalt temperature-±. 14° C (25° F) at the time of application to the substrate

expansion joint – a structural separation between two building elements that allows free movement between the elements without damage to the roofing or waterproofing system

exposure – (1) the transverse dimension of a roofing element not overlapped by an adjacent element in any roofing system. The exposure of any ply in a membrane may be computed by dividing the felt width minus 51 nun (2in), by the number of shingled plies; thus, the exposure of a 914-mm (30in) wide felt in a shingled, four-ply membrane should be 210 111m (8 1/2 in); (2) the time during which a portion of a roofing element is exposed to the weather

extra steep asphalt – See super-steep asphalt

fabric – a woven cloth of organic or inorganic filaments, threads, or yarns

factory square – 10m2 (l08 ft)

fallback – a reduction in bitumen softening point, sometimes caused by refluxing or overheating in a relatively closed container. (See also softening point drift)

felt – a flexible sheet manufactured by the interlocking of fibers with a binder or through a combination of mechanical work, moisture, and heat. Felts are manufactured principally from vegetable fibers (organic felts), asbestos fibers (asbestos felts), or glass fibers (glass fiber felts); other fibers may be present in each type
felt layer – (1) a machine used for applying bitumen and built-up roofing felts; (2) See Ply

felt mill ream – the mass in pounds of 480 ft’ of dry, unsaturated felt, also termed “point weight”

fine mineral surfacing – water-insoluble inorganic material, more than 50% of which passes the 500-um (No. 35) sieve, used on the surface of roofing

finger blisters – finger-shaped blisters or tinkles in the plies of a built-up roofing or waterproofing membrane

finger wrinkles – See finger blisters

fishmouth – (1) a half-cylindrical or half-cortical opening formed by an edge wrinkle or failure to imbed a roofing felt; (2) in shingles, a half-conical opening formed at a cut edge

flashing – the system used to seal membrane edges at walls, expansion joints, drains, gravel stops, and other places where the membrane is interrupted or terminated. Base flashing covers the edges of the membrane. Cap or counterflashing shields the upper edges of the base flashing

flashing cement – a trowelable mixture of cutback bitumen and mineral stabilizers including asbestos or other inorganic fibers

flat asphalt – a roofing asphalt confom1ing to the requirements of Specification D 312, Type 11

flood coat – the top layer of bitumen used to hold the aggregate on an aggregate-surfaced, built-up roofing membrane

fluid-applied elastomer – an electrometric material, fluid at ambient temperature, that dries or cures after application to form a continuous membrane. Such systems normally do not incorporate reinforcement

flux – a bituminous material used as a feedstock for further processing and as a material to soften other bituminous materials
“free carbon” in tars – the hydrocarbon fraction that is precipitated from a tar by dilution with carbon disulfide

glass felt – glass fibers bonded into sheets with resin and suitable for impregnation in the manufacture of bituminous, waterproofing, roofing membranes, and shingles
glass mat – a thin mat of glass fibers with or without a binder

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 plie or top ply of built-up membrane, when application of additional felts, or the nood coat and aggregate surfacing are delayed
granule – See mineral granules

gravel – coarse, granular aggregate, with pieces larger than sand grains, resulting from the natural erosion of rock

gravel in – to spread aggregate into hot bitumen on the surface of the roofing membrane

gravel stop – a flanged device, frequently metallic, designed to prevent loose aggregate from washing off the roof and to provide a continuous finished edge for the roofing

headlap – the minimum distance, measured at 90 degrees to the eave along the face of a shingle or felt as applied to a roof, from the upper edge of the shingle or felt, to the nearest exposed surface

holiday – an area where a liquid-applied material is missing
“hot stuff” or “hot” – a roofer’s term for hot bitumen

hygroscopic – attracting, absorbing, and retaining atmospheric moisture

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, an ice dam may cause ice to and water to back up under shingles and other roofing materials.

incline – the slope of a roof expressed in percent or in the number of vertical units of rise per horizontal unit of run

inorganic, adj. – being or composed of matter other than hydrocarbons and their derivatives, or matter that is not of plant or animal origin

kerosine number – the milliliters of kerosine held per 100 g of felt as determined by Method D 727. To obtain the percentage saturating capacity of the felt for any bituminous saturant, obtain the specific gravity of the saturant and multiply that figure by the kerosine number of the felt

knot – an imperfection or nonhomogeneity in materials used in fabric construction, the presence of which causes surface irregular ties

liquid bituminous material – one having a definite volume but no definite form, except as provided by its container. It has a viscosity of 0.1 to I x 105 cSt (mm2/s) at 40° C. This does not include powders or granular materials.

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

lot – in roofing, (1) production lot – all material produced in one eight-hour shift of the same type (and color when applicable); (2) delivery lot ­all material of the same type delivered at one time by one truck or railroad car

mastic – See flashing cement and asphalt mastic.
membrane – a flexible or semi-flexible roof covering or waterproofing, whose primary function is the exclusion of water

mesh – the square opening of a sieve
metal flashing – See flashing; frequently used as a through wall, cap, or counter-flashing mineral fiber felt – a felt with rock wool as the principal component

mineral granules – opaque, natural, 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 semisolid bituminous materials

mineral-surfaced roofing – built-up roofing whose top ply consists of a granule-surfaced sheet

mineral-surfaced sheet – a felt that is coated on one or both sides with asphalt and surfaced with mineral granules

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 bitumen with a mop or mechanical app1icalOr to the substrate or to the plies of a built-up roof. There are four types of mopping; (1) solid- a continuous coating; (2) spot – bitumen is applied in roughly circular areas, generally about 460 mm (18 in) in diameter, leaving a grid of unmopped; (3) strip – bitumen is applied in parallel bands, generally 200 mm (8 in.) wide and 300 mm (12 in) apart; (4) sprinkle ­bitumen is shaken onto the substrate from a broom or mop in a random pattern

mud cracking – surface cracking resembling a dried mud flat.

nailing – (1) exposed-nailing of roofing wherein nail heads are bare to the weather; (2) concealed-nailing of roofing wherein nail heads are concealed from the weather. (See also blind nailing)

neoprene – a synthetic rubber (polychloroprene) used in liquid-or sheet-applied elastometric roofing membranes or flashing

nineteen-inch selvage – a prepared roofing sheet with a 432-mm (17 in.) granule-surfaced exposure and a 483-mm (19 in.) selvage

ninety- pound – a prepared roll roofing with a granule-surfaced exposure that has a mass of approximately 4400 g/m2 (90 Ib/108 ft2)

one-an-one – the application of a single ply of roofing over the substrate, followed by the application of a second single ply over the first (phased application)

organic, adj – being or composed of hydrocarbons or their derivatives, or matter of plant or animal origin

parting agent – a material applied to one or both surfaces of a sheet to prevent blocking

penetration – the consistency of a bituminous material expressed as the distance in tenths of a millimeter (0.1 mm) that a standard needle penetrates vertically, a sample of material under specified conditions of loading, time, and temperature. A cone is sometimes used for special purposes, instead of a needle

perlite – an aggregate used in lightweight insulating concrete and in preformed perlite insulating board; formed by heating and expanding siliceous volcanic glass

permeance – the rate of water vapor transmission per unit area at a steady state through a membrane or assembly, expressed in ng/Pa * s * m2 (grain/ft2 *h*in. Hg)

phased application – the installation of a roofing or waterproofing system during two or more separate time intervals; a roofing system not installed in a continuous operation
petroleum pitch – a dark brown to black, predominately aromatic, solid cementitious material obtained by the processing of petroleum, petroleum fractions, or petroleum residuals

picture framing – a rectangular pattern of ridges in a membrane over insulation or deck joints

pinhole – a tiny hole in a film, foil or laminate comparable in size to one made by a pin

pitch – See incline; coal tar pitch, or petroleum pitch

pitch pocket – a flanged, open-bottomed, metal container placed around a column or other roof penetration, and filled with hot bitumen or flashing cement to fill 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

plying cement – any bituminous material used for adhering layers of felts, fabrics, or mats to structural surfaces and to each other

pond – a surface that is incompletely drained

point weight – See felt mill ream

primer – a thin liquid bitumen applied to a surface to improve the adhesion of heavier applications of bitumen and to absorb dust

rake – the sloped edge of a roof at the first or last rafter

raspberry – See strawberry

recovering – the process of covering an existing roofing system with a new roofing system

reentrant corner – an inside comer of a surface, producing stress concentrations in the roofing or waterproofing membrane

reglet – a groove in a wall or other surface adjoining a roof surface for the attachment of counter flashing

reinforced membrane – a roofing or waterproofing membrane reinforced with felts, mats fabrics, or chopped fibers

relative humidity – the ratio of the mass per unit volume (or partial pressure) of water vapor in an air-vapor mixture to the saturated mass per unit volume (or partial pressure) of the water vapor at the same temperature expressed as a percentage

release agent – See parting agent

reroofing – the process of recovering or replacing an existing roofing system; see recovering

resistance, thermal – the average temperature difference between two defined surfaces of a particular body or assembly when unit thermal transmission in unit time through unit area is established between the surfaces. R = K * m2/fW (R = 0f * h * ft2/Btu).

ridging – an upward, tenting displacement of a membrane, frequently over an insulation joint

roll roofing – coated felts, either smooth cr mineral surfaced

roof cement – See flashing cement

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 – in roofing, 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 diamond-shaped base. See also cricket

sales square – the quantity of prepared roofing required to cover 93m2 (100 ft”) of deck

saturated felt – a felt that has been immersed in hot bitumen; the felt absorbs and absorbs as much bitumen as it can retain under the processing conditions, but remains porous and contains voids

screen – an apparatus with circular apertures for separating sizes of material

scuttle – a hatch that provides access to the roof from the interior of the building

sealant – a mixture of polymers, fillers, and pigments used to fill and seal joints where moderate movement is expected; unlike caulking, it cures to a resilient solid granule-surfaced roll roofing

shark fin – an upward-curled felt side lap or end lap

shingle – (1) a small unit of prepared roofing designed for installation with similar units in overlapping rows on inclines normally exceeding 25% cover with shingles; and 2) to apply any sheet material in overlapping rows like shingles

shingling – (1) the procedure of laying parallel felts so that one longitudinal edge of each felt overlaps, and the other longitudinal edge underlaps an adjacent felt. (See also ply), Normally, felts are shingled on a slope so that the water flows over rather than against each lap; (2) the application of shingles to a sloped roof

sieve – an apparatus with square apertures for separating sizes of material

skater’s cracks – curvilinear cracks in a roofing membrane that appear to relate to neither the direction of application of the membrane components nor the substrate components

slag – the fused agglomerate which separates in metal smelting and floats on the surface of the molten metal; see also blast furnace slag

slippage – the relative lateral movement of adjacent components of a built-up membrane; it occurs mainly in roofing membranes on a slope, sometimes exposing the lower plies or even the base sheet to the weather

slope – the tangent of the angle between the roof surface and the horizontal plane, expressed as a percentage, or in inches of rise per foot of horizontal distance; see also incline

smooth-surfaced roof – a built-up roof without mineral aggregate surfacing
softening point – the temperature at which a bitumen becomes soft enough to flow as determined by an arbitrary, closely defined method

softening point drift – a change in the softening point during storgae or application; see also fallback

solid bituminous material – one having a viscosity of over 1 x 10 55 cSt (mm2/s) at 400C or an equivalent viscosity at an agreed-upon temperature. This includes powders and granular materials.

solid mopping – See mopping

split – a membrane tear resulting from tensile stress

split sheet – See nineteen-inch selvage

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 9.29 m” (JOO ft”), or enough material to cover 9.29 m2 of deck

stack 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

steep asphalt – a roofing asphalt conforming to the requirements of 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

strip flashing – (1) the technique of sealing a joint between metal and built-up membrane with one or two plies of felt or fabric and hot or cold applied bitumen; (2) the technique of taping joints between insulation boards or deck panels

substrate – the surface upon which the roofing or waterproofing membrane is placed (structural deck or insulation)

sump – a depression around a drain

super-steep asphalt – a roofing asphalt conforming to the requirements of Specification D 312, Type IV

susceptibility – when not otherwise qualified, the degree of change in viscosity with temperature

tapered edge strip – a tapered insulation strip used to elevate the roofing at the perimeter and at penetrations of the roof.

tar – a brown or black bituminous material, liquid or semi-solid 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.

tear off – to remove an existing roofing system down to the structural deck.
thermal insulation – a material applied to reduce 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

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.

vapor barrier – See vapor retarder.

vapor migration – the movement of water vapor from a region of high vapor pressure to a region of lower vapor pressure.

vapor retarder – a layer of material or a laminate used to appreciably reduce the flow of water vapor into the roofing system.

vent – an opening designed to convey water vapor or other gas from inside a building or a building component into the atmosphere.

vermiculite – an aggregate used in lightweight insulating concrete, formed by heating and expanding a micaceous mineral.

viscoelasticity – a combination of viscous and elastic properties in a material, with the relative contribution of each dependent upon time, temperature, stress, and strain rate.

walk in – to imbed insulation panels in hot bitumen or adhesive by walking on them immediately after application.

waterproofing – treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.