Roofing Terms

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Term Definition
Absorption The ability of a porous, solid material to hold a relatively large quantity of liquid (or gas).
Adhesion Measured in shear and peel modes, this is the state in which two surfaces are held togegther by interfacial forces. These forces may consist of molecular forces, interlocking action, or both.
Adhesive Failure This is the separation of two bonded surfaces which occur at the interface between the adhesive and the material being bonded.
Aggregate This is often crushed stone, slag, or water-worn gravel used for surfacing a built-up roof. It can also refer to any granular mineral material.
Aging This is the effect environmental exposure has on a material after an interval of time. It also refers to the process of exposing materials to environmental conditions for a period of time.
Alligatoring This term refers to the shrinkage and/or cracking of the surfacing bitumen on a built-up roof. The result resembles an alligator's hide. The cracks may or may not extend through the entire surfacing bitumen thickness.
ANSI Americal National Standards Institute
Antidegradant This is a compounding material used to attempt to retard deterioration caused by oxidation, ozone, light, and/or a combination of these. It can also be used as a generic term for additives like antioxidants, antiozonants, and waxes.
Antioxidant A substance designed to prevent or retard oxidation of material exposed to air.
Approval drawings These are drawings, which may include framing drawings, elevations, or building sections, furnished by the manufacturer for approval of the buyer. Approval by the buyer signifies the manufacturer has correctly interpreted the overall contract requirements for the system and its accessories, and the exact location of these.
Architectural drawing A drawing that shows the plan view and/or elevations of the finished building to show the feneral appearance of the building and indicates all accessory locations.
Asbestos A group of natural fibrous impure silicate materials.
Asphalt A dark brown to black cementitious material whose predominating constituents are bitumens occuring in nature, or are created through petroleum processing.
Asphalt, air blown Air is blown through asphalt to raise softening point and modify other properties.
Asphalt, roof cement This is a trowelable mixture of asphalt, mineral stabalizers, fillers, and/or other fibers.
Asphalt, steam blown Similar to air blown asphalt, steam is blown through molten asphalt to modify properties.
Asphalt felt Felt saturated with asphalt.
ASTM Americal Society for Testing and Materials
AWS American Welding Society
Backup plate A rigid plate designed to support an end lap in a metal panel roof. This is to provide uniform compression.
Ballast Loose aggregate, concrete pavers, or other material used to prevent wind uplift or flotation of a loose-laid roof system.
Barrier protection A physical, inert barrier used as protection from the environment. If the barrier is broken, the underlying base metal is unprotected.
Base sheet A saturated or coated felt used as the first ply in a multi-ply bituminous roofing membrane.
Batten A raised rib in a metal roof. This can also be used to describe separate part or a formed portion in a metal roofing panel.
Bill of materials (BOM) A list of items or components used for fabrication, shipping, receiving, and accounting purposes.
Bitumen This is most often used to describe a class of amorphouse, black or dark colored, cementitous substances, either natural or manufactured, composed principally of high-molecular-weight-hydrocarbons, soluble in carbon disulfide, and found in asphalts, tars, pitches, and asphaltites. Bitumen is also used as a generic term for any material composed mainly of bitumen.
Bituminous A material containing or treated with bitumen.
Bituminous emulsion The suspension of small globules of bituminous material in water or another aqueous solution.
Blanket insulation Fiberglass insulation in a roll form. This is frequently installed between metal roof panels and the supporting purlins.
Blister This is a raised portion of a roof membrane caused by interal pressure in an air-water-vapor pocket trapped between either the membrane and its substrates or between membrane layers.
Blister - polyurethane foam An undesirable rounded delamination of the surface of polyurethane foam. The boundaries may or may not be sharply defined.
BOCA Building Officials and Code Administration
Bond Adhesive and cohesive forces holding two components in intimate contact.
Boot This is a bellows-like covering to exclude dust, dirt, moisture, etc., and forms a flexible closure.
Builder/Contractor A general contractor or subcontractor responsible for providing and errecting building systems.
Building code Published regulations and ordinaces describing design loads, procedures, and construction details for structures, established by a recognized agency.This usually controls design, construction, material quality, use and occupancy, location, and maintenance for a specific area.
Built-up roofing (BUR) A continuous semiflexible membrane consisting of plies of saturated felts, coated felts, fabrics, or mats, which are assembled in place with alternate layers of bitumen. This is surfaced with mineral aggregate, bituminous material, or a granule sufaced sheet.
Bull A roofer's term used for flashing or plastic cement.

Butyl rubber

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A synthetic rubber based on isobutylene and a minute amount of isoprene. Vulcanizable, this features a low permeability to gasses and water vapor. It is also relatively resistant to aging, chemicals, and weathering.
Canopy Any overhang from the roof - usually with an unsupported end.
Cap sheet A granule-surfaced coated felt used as the top ply of a built-up or modified bituminous roofing membrane.
Caulk To seal joints, seams, or voids through filling the area with a waterproofing compound or material.
Caulking A composition made of vehicle and pigment that is used at ambient temperatures for filling joints. Caulk remains plastic for an extended period of time after application.
Cavity wall A wall built of hollow masonry units which are arranged to provide a continuous internal air space.
Coal tar A dark bown to black cement-like material which is produced through destructive distillation of coal.
Coal tar felt

A felt that is saturated with refined coal tar.

Coal tar pitch A dark brown or black, solid cement-like substance that is obtained as a residue from the parital distallation or evaporation of coal tar.
Coated fabric A fabric coated with a plastic solution, dispersion hot melt, or powder.
Coated sheet or felt An asphalt felt which has been coated on both sides with a more viscous asphalt or a glass-fiber felt that has been impregnated and coated with asphalt on both sides.
Coating weight This is the weight of a surface coating, usually expressed in ounces per square foot (or grams per square meter).
Collector box This is the transition piece between a gutter and a downspout. It is designed to faciliate water flow.
Condensation Part of the conversion of water vapor to a liquid state as the temperature cools or there is a rise in atmospheric pressure.
Conductivity - electrical The reciprocal of electrical resistance.
Cool Roof Rating Council (CRRC) The council establied to provide radiative data on roof surfaces to the building industry.
Coping A covering on top of an exposed wall. This is usually sloped for water drainage.
Counterflashing Made of formed metal or elastomeric sheeting, this piece is secured on or into a wall, curb, pipe, rooftop unit, or other penetration, to shield the upper edge of a base flashing and it's fasteners from the weather.
Cricket This is generally a small elevated area of a roof which is contructed to divert water from a horizontal intersection of the roof with a projection such as a chimney, wall, or expansion joint.
Curb A raised area used for support of roof penetraitons such as skylights and hatches.
Cure The process of using heat, radiation, or reaction with chemical additives to change the properties of a polymetric system into a more usable compound.
Curled felt A defect of a built-up roof (BUR) membrane. This is charaterized by a continuous, open longitudinal seal where the top felt is rolled back from the bottom felt.
Top of PageDead-level Zero slope.
Deck This is the structural surface to which the roofing system is attached.
Delamination Separation of the piles in a membrane or separation of insulation layers after lamination.
Downspout This is a conduit used to move water from the gutter to the ground or storm drain.
Duck-board Slatted flooring laid on a wed, muddy, or cold surface.
Eave The line formed along a sidewall by the intersection of planes of the roof and wall.
Edge stripping This is the application of felt strips cut to narrower widths than the normal felt roll width used to dover a joint between a flashing a a bituminous roof.
Edge venting This refers to the practice of leaving protected openings at regular intervals to relieve water-vapor pressure in the insulation.
Elasticity The property of matter in which it regains orignial size and shape after the removal of stress.
Elastomer This refers to a macromolecular material which rapidly returns to its approximate initial dimenstions following a release of stress.
Emulsion A dispersion of fine particles of a liquid within a liquid.
End lap The overlapping ends of two panels.
Envelope A continuous edge seal formed by extending one ply of felt beyond the edge of the assembly. Once other plies are in place, the extended ply is turned back and adhered.
EPDM Ethylene propylene diene monomer - a type of roofing membrane.
Expansion joint A structural separation between two building elements to allow free movement in the form of expansion and contraction without damage to the roofing system.
Fabrication A manufacturing process performed in a plant which converts raw materials into finished components.
Fascia This is a decorative trim projecting from the face of the wall. It serves as a weather closure.


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A flexible sheet manufactured by the interlocking of fibers through mechanical means, moisture, and heat. Roofing felts are made from vegetable fibers, glass fibers, or polyester fibers and are not spun, woven, or knitted.
Fiberglass insulation This ia a blanket insulation comprised of glass fibers to insulate roofs.
Flashing cement This is a mixture of cutback bitumen, mineral stabilizers, and fibers.
Flat asphalt A roofing asphalt that conforms to Specification D312, Type II.
Gravel Coarse, granular aggregate, with pieces larger than grains of sand. This is a result of the natural erosion of rock.
Gravel stop This is a device designed to prevent loose aggregate from washing off the roof.
Gutter A channel installed at the eave of a roof to carry water to a drain or the ground.
"Hot stuff" or "Hot" A roofer's term for hot bitumen.
Incline The slope of a roof expressed in percent or in the number of vertical units of rise over run.
Isotherm This refers to the line on a display screen that indicates equal apparent temperatures. On an imaging scanner, this is highlighted on the display as white.
Joist A small beam arranged parallel from wall to wall to support a floor, ceiling, or roof.
Kick-out (elbow) A lower portion of a downspout which directs water away from a wall.
Lap The area where a felt covers an underlying felt in a BUR membrane. This term is also used in single-ply membranes. An end lap occurs at the end of a roll, while an edge lap indicates a transverse cover.

Lapped joint

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This term applies to an joint made by placing one surface to be joined partly over another surface to be joined and bonding the overlapping area.
LEED Leadership in Energy and Enviornmental Design
Life-cycle costing This analytical technique allows for a systematic comparison of economic alternatives over the useful lifetime of the assest or product.
Maintenance and Repair Cost The total cost of labor, materials, and other related costs which are incurred for preventative maintenance or repair to an asset.
Masonry Anything built from bricks, concrete blocks, concrete, or a similar stone material.
Membrane This term is used to describe any flexible or semiflexible roof covering with the primary function to exclude water.
Metal flashing This is frequently used as a through-wall cap flashing or counterflashing.
Mopping This is the process of applying hot bitumen to a built-up or modified bitumen roofing system.
Neopreme This is a synthetic rubber used in either liquid or sheet applied elastomeric roofing membranes or flashing.
Parapet The portion of a wall above the roof line.
Perlite This is an aggregate that is used in lightweight insulating concrete and preformed perlite insulating boards. It is formed by heating and expanding siliceous volcanic glass.
Phased application The process of installing a roofing system during two or more separate time intervals.
Ply A layer in a roofing membrane is called a ply.
Pond A roof area which reatins water instead of draining after a rain.
Ponding Water which remains in a low or irregular roof area for more than 48 hours after a rain.
Preventative maintenance Regular, scheduled inspection of a roofing system to repair normal breakdown.
Reroofing This is the replacement of a defective roofing system with a new one.
Retrofit The modificaqtion of an existing building to include a new system.
Ridge This refers to the highest point of the roof of a building - generally a horizontal line running the entire length.
Ridge cap This refers to the transition of the roofing material along the ridge of a roof.
RIEI Roofing Industry Educational Institute

Roll roofing

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This term refers to coated felts which are either smooth or mineral-surfaced. Roofing materials which come in a roll.
Roof covering This is the exposed area of the roof.
Roof curb This refers to an accessory used to mount and level units such as HVAC on a sloped portion of a roof.
Roof jack This accesssory covers pipes (vents or flues) which penetrate the roof panel.
Roof overhang A roof extension beyond the endwall of a building is called a roof overhang.
Roof system This refers to the weatherproofing, insulating, and protective system designed to cover a building.
Sacrificial protection An example of this is galvanic protection. This process reduces the extent of corrosion of a metal in an electrolyte by coupling it to another metal which is electrochemically more active in the environment.
SBA System Builders Association
SBC Standard Building Code
SBCCI Southern Building Code Congress International
Scrim Used in the reinforcement of polymeric sheeting, this is an open-mesh fabric woven from continuous-filament yarn.
Scupper This is a channel through a parapet wall designed for drainage of the roof, usually as a safety overflow to limit ponded water caused by a clogged drain.
Sealant This ia a material used to close cracks or joints in a roofing system for leak protection. For example: Lap sealant is applied to exposed lap edges.
Sealing washer This is a rubber washer with a metal back which is assembled on a screw to prevent water migration through the screw hole.
Seam strength This refers to the strength of a seam of material. Measured in shear or peel mode, this is reported in absolute units like pounds per inch of width, or as a percent of the sheeting strength.
Service life The anticipated useful life of a building, component, or sub-system. For example: roofing system.
Shark fin This term refers to the curled felt projecting upward thgouth the flood coat and aggregate of a BUR membrane.
SI The international system of metric units.
Side lap The continuous overlap of closures along a side panel.
Single slope A sloping roof with one surface.
Skylight This is a rooftop acessory designed to admit light - usually mounted on a curb.
Slippage Relative lateral movement of adjacent felts or sheets in a roofing membrane. Most often seen on sloping roofs, this sometimes exposes the lower plies or base sheet to the elements.
Slope Expressed as a percentage of rise per foot of horizontal distance, this is the tangenet of the angle between the roof surface and the horizontal plane.
Smooth-surface roof This is a roof membrane without aggregate.
Soffit This refers to the covering of the underside of a roof's exterior overhang, sidewall, or gable.

Solar reflectance index (SRI)

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The SRI is the measure of a roof's ability to reflect solar heat. This is shown by a small temperature rise, defined so that a standard black is 0 and a standard white is 100. The calculation of SRI follows the ASTM method E1980.
Square A roof area of 100 square feet.
Stack vent This is a vertical outlet designed to relieve pressure exerted by water vapor between a membrane and the deck (or a vapor retarder).
Stainless steel With an excellent reistance to corrosion, this steel alloy contains a high percentage of chromium. It may also contain nickel or copper.
Standing water test An evaluation in which test panels are submerged in aqueous solutions and then air dried.
Strain Deformation of a material under stress.
Stress A measure of the load on a structural member in terms of force per unit area or the force acting across a unit area in a solid material in resisting the separation, compacting, or sliding that may be induced by external forces.This term also applies to the ratio of applied load.
Substrate This is the surface that a roof component is placed, like a structural deck or insulation.
Tar boils Also known as blueberries, blackberries, and strawberries, these are bubbles of moisture vapor encaled in a thin film of bitumen.
Tearoff This term refers to the removal of a failed or expired roof system down to the deck surface.
Thermal conductance (C) This is the rate of heat flow in Btus per hour through a square foot of material - or combination of materials - with surfaces having a temperature differential of 1 degree F..
Thermal conductivity (k) THis is the rate of heat flow in Btus per hour through a square foot of material exactly one inch thick with a temperature differential of 1 degree F.
Themal insualation Any material designed to reduce conductive heat flow.
Thermal resistance (R) This is resistance to heat flow and the reciprocal of conductance (C).
Thermal shock This is stress caused by sudden temperature drops in a roof membrane. For example, thermal shock my occur when a rain storm follows a warm, sunny day.
Thermogram This refers to the visible light record of a infrared camera system display.
Thermography This technique produces heat pictures from the radiant energy emitted from a stationary or moving object without influencing the temperature in any way. This results in an electronic display of a visible image of an infrared spectrum.

Time value of money

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The theory that money available at the present time is worth more or less than the same amount at a future date due to inflation or deflation. This is also called the present discounted value. This term is also used to refer to the changes in purchasing power and the real earning potential of an investment over time.
TPO TPO is a weldable thermoplastic sheet used as a single-ply membrane.
Trim Often referred to as flashing, this is a lightgage metal used to finish a building, particularly around openings and at intersections of surfaces.
UBC Uniform Building Code

Vapor barrier

Vapor retarder

A material which resists the flow of water vapor
Vent This is an opening designed to allow the emittance of water vapor or other gasses from the inside of a building.
Ventilator A ventilator is an accessory typically used as a pass-through for air.
Vermiculite This aggregate is used in lightweight insulating concreate and is formed through the heating and expansion of a micaceous material.
Viscosity Measured in centistokes (cSt) for bitumens, this is the index of a fluid's internal resistance to flow. Water has a viscosity of 1 cSt. Light cooking oil has a viscosity of 100 cSt.
Vulcanization This irreversible process changes the chemical structure of a rubber compound to amke it less plastic and more resistant to swelling by orgainc liquits. This improves, conferrs or extends the elastic properties over a greater temperature range.
Warp This is the lengthwise yarns in a woven fabric.
Waterproofing The treatment of a surface as a preventative for the passage of water under hydostatic pressure.
Wind uplift The upward-acting pressure which results from air motion across a roof.

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Griffin, C. W., & Fricklas, R. L. (2006). Manual of low-slope roof systems. (4th ed.). New York: McGraw-Hill.