Roof Terms & Anatomy

Absorbtion
The act or process of retaining foreign particles such as gas or liquid without transmission of these particles.

Acid Etch
The use of a strong acid to remove the surface of concrete thereby exposing the aggregate. The use of a strong acid to etch the surface of material such as metal in order for that material to accept a primer or Spray Polyurethane Foam.

Acrylic Coating
A coating system with an acrylic resin base.

Acrylic Resin
Polymers of acrylic or methacrylic monomers often used as a latex base for coating systems.

Active
Will corrode in the presence of moisture or a “noble” metal.

Adhere
The clinging of one surface to another; either molecularly or otherwise.

Adhesion
The state of adhering.

Aggregate
A surfacing or ballast for a roof system. Aggregate can be rock, stone, crushed stone or slag, water-worn gravel, crushed lava rock or marble chips.

AHA
American Hardboard Association

AIA
American Institute of Architects

Air Blown Asphalt
Asphalt produced by blowing air through molten asphalt held at an elevated temperature. This procedure is used to modify properties of the asphalt.

Alligatoring
The cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks that resemble an alligator’s hide.

Aluminized Steel
Sheet steel with a thin aluminum coating on the surface to enhance the steel’s ability to withstand weathering.

Aluminum
A non-rusting metal used in roofing for metal roofing and the fabrication of gutter and flashings.

Ambient Temperature
The temperature of the air.

Anodic
When two metals are connected in an electrolyte, they will form a galvanic cell, with the higher metal in the galvanic series being the anode. The anodic will oxidize and produce an electrical current which protects the cathode from corrosion.

ANSI
American National Standards Institute

APA
American Plywood Association

APP
See Atactic Polypropylene.

Application Rate
The rate at which a material is applied per unit area.

Apron Flashing
A flashing located at the low end of a curb or penetration.

Architectural Panel
A metal roof panel that usually requires solid decking underneath.

Architectural Shingle
Shingle that provides a dimensional appearance. See also Dimensional Shingle.

Area Divider
A flashed assembly usually extending above the surface of the roof that is anchored to the roof deck. It is used to relieve thermal stresses in a roof system where an expansion joint is not required, or to separate large roof areas.

ARMA
Asphalt Roofing Manufacturers Association

ASA
American Subcontractors Association

Asbestos
An incombustible fibrous mineral form of magnesium silicate formerly used for fireproofing and sometimes used for the reinforcement of roofing materials.

ASC
Associated Specialty Contractors

ASHI
American Society of Home Inspectors

ASHRAE
American Society of Heating, Refrigerating & Air-Conditioning Engineers, Inc.

Asphalt
A substance left as a residue after evaporating or otherwise processing crude oil or petroleum. Asphalt can be refined to conform to various roofing grade specifications: Dead-Level Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type I. This asphalt is for use in roofs which do not exceed a ¼ in 12 slope (2%). Flat Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type II. This asphalt is for use in roofs which do not exceed a ½ in 12 slope (4%). Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type III. This asphalt is for use in roofs which do not exceed a 3 in 12 slope (25%). Special Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type IV. This asphalt is for use in roofs which do not exceed a 6 in 12 slope (50%).

Asphalt Emulsion
A mixture of asphalt particles and an emulsifying agent such as bentonite clay and water.

Asphalt Felt
An asphalt-saturated and/or an asphalt-coated felt membrane. (See also Felt.)

Asphalt Primer
See Primer.

Asphalt Roof Cement
The proper name for Plastic Cement and Flashing Cement. Asphalt roof cement consists of solvent-based bitumen, mineral stabilizers, and other fibers (sometimes asbestos). Asphalt roof cement is categorized by ASTM standard D 2822-91 (1997) or for non-asbestos, ASTM standard D 4586-93. Plastic Cement is for use on low-slope surfaces, conforms to ASTM Specification D 312, Type I; Specification D 449, Types I or II; or Specification D 946. Plastic Cement is self-sealing, adhesive and ductile and is classified by ASTM Standard D 2822-91 Asphalt Roof Cement, and D 4586-92 Asphalt Roof Cement, Asbestos-Free, Types I and II. Flashing Cement can be used on vertical surfaces and has a high softening point, low ductility and conforms to the requirement of ASTM Specification D 312, Types II or III; or Specification D 449, Type III.

Asphalt Shingles
(1) A single piece of prepared roofing material, either asphalt or wood, for use in steep slope roof systems. (2) To install a wood or asphalt shingle roof system.

ASTM
American Society for Testing and Materials

Atacic Polypropylene
A group of high molecular weight polymers formed by the polymerization of propylene.

Attic
The open area above the ceiling and under the roof deck of a steep-sloped roof.

AWPA
American Wood Preservatives Association

AWS
American Welding Society

Back-Nailing
The method of fastening the back or upper side of a ply of roofing felt or other component in a roof system so that the fasteners are covered by the following ply.

Back-Surfacing
A fine mineral material on the back side of roofing materials such as roll roofing to keep them from sticking together while packaged.

Ballast
A material installed over the top of a roof membrane to help hold it in place. Ballasts are loose laid and can consist of aggregate, or concrete pavers.

Bar Joist
See Steel Joist

Barrel Roof
A roof configuration with a partial cylindrical shape to it.

Base Flashing
(membrane base flashing): Plies of roof membrane material used to seal a roof at the vertical plane intersections, such as at a roof-wall and roof-curb junctures. (See also Flashing.)

Base Ply
The primary ply of roofing material in a roof system.

Base Sheet
An asphalt-impregnated, or coated felt used as the first ply in some built-up and modified bitumen roof systems.

Batten
(1) A strip of wood usually fastened to the structural deck for use in attaching a primary roof system such as tile; (2) A plastic strip, wood strip, or metal bar which is used to fasten or hold the roof and/or base flashing in place, A.K.A. Termination Bar.

Bermuda Seam
A metal roof that has a step profile.

Bird Bath
Small, inconsequential amounts of water on a roof that quickly evaporate.

Bird Screen
Wire mesh installed over openings in order to prevent birds from entering a building or roof cavity.

Bitumen
Any of various flammable mixtures of hydrocarbons and other substances, occurring naturally or obtained by distillation from coal or petroleum, that are a component of asphalt and tar and are used for surfacing roads and for waterproofing.

Bitumen-Stop
A continuous seal for preventing bitumen from leaking down into or off a building. Is constructed by extending the base sheet or other non-porous ply of felt beyond the edge of the field plies. It is then turned back onto the top of the system and adhered. See also Envelope.

Bituminous Emulsion
Bituminous particles suspended in water or other solution. See also Asphalt Emulsion.

Blackberry
See Tar Boil

Bleeder Strip
A starter strip placed along rake edges for use in asphalt shingle roofing. See also Rake-Starter.

Blind-Nailing
The use of nails so that they are not exposed to the weather in the finished roofing system. See Back-Nailing

Blister
A pocket of air trapped between layers of felt or membrane. Blisters are usually caused by water or other foreign substances.

Blocking
Pieces of wood built into a roof assembly used to stiffen the deck around an opening, support a curb, or for use as a nailer for attachment of membranes or flashing.

Blown Asphalt
See Air Blown Asphalt

Blue-Tee
A steel reinforcing member used when constructing pre-stressed, poured gypsum decks. When the gypsum is poured, it surrounds the Bult-Tee.

Blueberry
A small bubble found in the flood coat of an aggregate-surfaced built-up roof. See also Tar Boil.

BOCA
Building Officials and Code Administrators, International, Inc.

BOMA
Building Owners & Managers Association, International

Bond
The force(s) holding two components in positive contact.

Bonding Agent
A chemical agent used to create a bond between two layers.

Boot
A piece of material preformed to protect roof penetrations from dirt, moisture and other foreign and/or damaging substances.

Brake
A piece of equipment used for forming metal.

Bridging
When membrane is unsupported at a juncture.

British Thermal Unit
(BTU): The heat energy necessary to raise the temperature of one pound of water one degree Fahrenheit, a joule.

Brooming
Embedding a ply of roofing material into hot bitumen or adhesive by using a broom, squeegee, or other piece of equipment to eliminate voids and help ensure adhesion.

Buckle
A long, tented displacement of a roof membrane. Can occur over insulation and deck joints.

Built-Up Roof Membrane
A roof membrane consisting of layers of bitumen, which serves as the waterproofing component, with plies of reinforcement fabric installed between each layer. The reinforcement material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate, emulsion or a granule-surfaced cap sheet.

Bundle
An individual package of shingles or shakes.

BUR
An acronym for Built-Up Roof. See Built-Up Roof.

Butadiene
A colorless, highly flammable hydrocarbon, C4H6, obtained from petroleum and used in the manufacture of synthetic rubber.

Butly
A hydrocarbon radical, C4H9. Butyl has a rubber-like consistency, is formed from the copolymerization of isobutylene and isoprene and is used primarily in sealants and adhesives.

Butt Joint
Where two separate, adjacent pieces of material abut.

Butyl Rubber
A butyl-based, synthetic elastomer.

Butyl Tape
A sealant tape used in numerous sealant applications such as sealing sheet metal joints.

C-Channel
A structural framing member that, when viewed cross-sectionally, has the shape of a “C”.

CABO
Council of American Building Officials

Calender
A machine used to laminate sheeting or for applying coating with a specified thickness and/or surface attribute.

Calendering
A specific process used to manufacture some membranes such as PVC.

Camber
A slight convex curve of a surface.

Canopy
An overhang, usually over entrances or driveways.

Cant
(1) Short for Cant Strip; (2) The act of installing foam at a right angle adjunct.

Cant Strip
A triangular-shaped strip of material used to ease the transition from a horizontal plane to a vertical plane. Cant strips can be made of wood, wood fiber, perlite, or other materials.

Cap Flashing
A material used to cover the top edge of base flashings or other flashings. (See also Coping)

Cap Sheet
A granule-surfaced membrane often used as the top ply of BUR or modified roof systems.

Capacitance Meter
A device for locating moisture within a roof system by measuring the ratio of the change to the potential difference between two conducting elements that are separated by a non-conductor.

Catalyst
A substance that effects a chemical reaction and/or the rate at which a chemical reaction takes place. In roofing, catalysts are used in SPF roofing.

Cathodic
Metals low in the Galvanic Series.

Caulk
A material with no elastomeric properties used for sealing joints

Caulking
The act of sealing a joint or of material.

Cavitation
The vaporization of a liquid under the suction force of a pump which can create voids within the pump supply line. Cavitation will result in off-ratio foam in Sprayed Polyurethane Foam applications.

CCF
100 cubic feet.

Cellulose
A complex carbohydrate, (C6H10O5)n, that is composed of glucose units, forms the main constituent of the cell wall in most plants, and is used in the manufacturing of organic roofing materials.

CERL
Construction Engineering Research Laboratory

CG&E
See Chopped Glass and Emulsion.

Chalk
Powdery residue on the surface of a material.

Chalk Line
(1) A string on a reel in a container that can hold chalk; (2) A line made on by pulling taut a string coated with chalk and snapping it.

Channel Flashing
Flashing with a built-in channel for runoff; used where roof planes intersect other vertical planes.

Chemical Resistance
A materials ability to retain its properties when it comes into contact with certain chemicals.

Chlorinated Polyethylene
(CPE): CPE is a flexible material with high tear strength, good chemical resistance and patency towards UV radiation. As a result of the high chlorine content (typically 30%) it is inherently difficult to ignite, but releases hydrogen chloride during combustion. It suffers from an extremely high permeability to gas. Resistance to most inorganic chemicals is generally good, while resistance to hydrocarbons increases with increasing chorine content. The material is used mainly as an impact modifier for PVC and, to a lesser extent, LDPE and HDPE film.

Chlorosulfonated Polyethylene
A synthetic, rubber-like thermoset material, based on high molecular weight polyethylene with suphonyl chloride, usually formulated to produce a self-vulcanizing membrane. Chlorosulfonated Polyethylene or CSPE. Best know as Hypalon™, it was developed in 1951 by DuPont.

Chopped Glass and Emulsion
(CG&E): A roof coating that consists of asphalt or clay emulsion and glass fiber reinforcement. The glass fiber comes in rope form and is mechanically chopped into small pieces and then mixed with the emulsion at the end of the spray gun so that the mixture is complete by the time the surfacing hits the top of the roof. Standard mixture is 9 gallons of emulsion and 3 pounds of glass fiber for every 100 square feet (36.5 Liters of emulsion and 1.5 kg of chopped glass for every 10 square meters). The CG&E coating is then usually surfaced with a fibered aluminum roof coating at rate of 1.5 gallons per 100 square feet (6 Liters per 10 square meters).

Cladding
A material used to cover the exterior wall of a building.

Cleat
A continuous metal strip used to secure two or more metal roof components together. Commonly used along with coping or gravel stop on tall buildings.

Clerestory
(Clearstory): A room that extends above an abutting roof section of a building.

Clip
A small cleat. See Cleat.

Clipped Gable
A gable cut back at the ridge in a small hip configuration.

Closed-Cut Valley
A method of valley application in which shingles from one side of the valley extend across the valley while shingles from the other side are installed over the top of those and then trimmed back approximately 2 inches from the valley centerline.

Closure Strip
Material used to close openings created by joining metal panels or sheets and flashings.

Coal Tar Bitumen
A proprietary trade name for Type III coal tar used in dead-level or low-slope built-up roofs. It is not for use in roofs exceeding ¼” in 12″ (2%) slope.

Coal Tar Felt
A roofing membrane saturated with refined coal tar.

Coal Tar Pitch
A type of coal tar used in dead-level or low-slope built-up roofs. It is not for use in roofs exceeding ¼” in 12″ (2%) slope.

Coal Tar Roof Cement
A trowelable mixture of processed coal tar base, solvents, mineral fillers and/or fibers.

Coarse Orange Peel Surface Texture
A surface showing a texture where nodules and valleys are approximately the same size and shape. This surface is generally acceptable for installing a protective coating.

Coated Base Sheet
An asphalt-saturated base sheet membrane later coated with harder, more viscous asphalt, thereby increasing its impermeability to moisture.

Coated Felt
An asphalt-saturated ply sheet that has also been coated on both sides with harder, more viscous asphalt.

Coating
A layer of material that is spray, roller, or brush applied over a surface for protection or sometimes decoration.

Cohesion
Mutual attraction by which the elements or particles of a body or substance are held together.

Coil Coating
The application of a finish to a coil of metal or other material.

Cold Forming
The process of shaping metal into desired configurations at ambient room temperature.

Cold Process Built-Up Roof
Roof consisting of multiple plies of roof felts laminated together with adhesives that usually come right out of a can or barrel and require no heating.

Collector Head
A component used to direct water from a through-wall scupper to a downspout. Also known as a Conductor Head.

Column
A vertical structural member placed on a footing or foundation used to support horizontal above-ground building components.

Combing Ridge
A term used to describe an installation of finishing slate at the ridge of a roof whereby the slates on one side project beyond to the apex of the ridge.

Combustible
Capable of igniting and burning.

Composition Shingle
A type of shingle used in steep-slope roofing and generally comprised of weathering-grade asphalt, a fiber glass reinforcing mat, an adhesive strip, and mineral granules.

Compounded Thermoplastics
A category of roofing membranes made by blending thermoplastic resins with plasticizers, various modifiers, stabilizers, flame retardants, UV absorbers, fungicides, and other proprietary substances, alloyed with proprietary organic polymers. Some of the membranes listed in this generic category are CPA, EIP, NBP, and TPA.

Concealed-Nail Method
A method of installing asphalt roll roofing material in which all nails or fasteners are driven into the underlying roofing and covered by an overlapping course.

Condensate
The liquid resulting from condensation.

Condensation
The conversion of water vapor to liquid state when warm air comes in contact with a cold surface. (See also Dew Point.)

Conduction
The transmission or conveying of something through a medium or passage, especially the transmission of electric charge or heat through a conducting medium without perceptible motion of the medium itself.

Conductor Head
A component used to direct water from a through-wall scupper to a downspout. Also known as a Collector Head.

Construction Joint
A constructed joint where two successive installments of concrete come together.

Contact Cements
Adhesives used to adhere or bond roofing components.

Coping
The piece of material used to cover the top of a wall and protect it from the elements. It can be constructed from metal, masonry, or stone.

Copper
A reddish-brown element that conducts heat and electricity very well. It is also used as a primary roof material as well as a flashing component. Copper turns a greenish color after being exposed to the weather for a length of time and appears in the middle of the Galvanic Series.

Cornice
A horizontal projecting part that crowns the wall of a building.

Counter Batten
Wood strips installed vertically on sloped roofs over which horizontal battens are secured.

Counterflashing
Formed metal sheeting secured to walls, curbs, or other surfaces, for use in protecting the top edge of base flashings from exposure to weather.

Course
(1) The term used for each row of roofing material that forms the roofing or flashing system; (2) One of multiple layers materials applied to a surface. For example, a three-course flashing consists of a layer of mesh or other reinforcing material sandwiched between two layers roofing cement.

Cove
In roofing, a heavy bead of sealant material installed at the point where vertical and horizontal planes meet. It is used to eliminate the 90° angle. See also Fillet.

Cover Plate
A metal strip sometimes installed over the joint between formed metal pieces.

Coverage
The surface area covered by a material.

CPA
Copolymer Alloy.

CPE
Chlorinated Polyethylene.

Crack
A separation or fracture occurring in a material. See also Split.

Cream Time
Time in seconds at a given temperature when the A and B (isocyanate and resin) components of SPF will begin to expand after being mixed.

Creep
Movement of roof membrane causing the roof system to be deformed

Cricket
A roof component used to divert water away from curbs, platforms, chimneys, walls, or other roof penetrations and projections. See also Saddle.

Cross Ventilation
The effect of air moving through a roof cavity between vents.

Crow's Nest
See Cupola.

CRREL
Cold Regions Research and Engineering Laboratory

CSI
Construction Specifications Institute.

CSM
ASTM designation for Chlorosulfonated polyethylene. (See CSPE.)

CSPE
Chlorosulfonated polyethylene.

Cupola
A relatively small roofed structure set on the ridge of a main roof area. Also known as a Crow’s Nest.

Curb
(1) A raised member used to support skylights, HVAC units, exhaust fans, hatches or other pieces of mechanical equipment above the level of the roof surface, should be a minimum of eight inches (8″) in height; (2) A raised roof perimeter that is relatively low in height.

Cure
A process by which a material is forms permanent molecular linkages by exposure to chemicals, heat, pressure, and/or weathering.

Cure Time
The time necessary to effect curing.

Curing Agent
A material additive that alters chemical activity between the components resulting in a change in the rate of cure.

Curing Compound
A liquid that is applied to newly installed concrete which slows water loss while curing.

Cutback
Bitumen thinned by solvents that is used in cold-process roofing adhesives, roof cements, and roof coatings.

Cutout
The open area between shingle tabs. Also known as a “throat”.

Cutt-off
A detail designed to seal and prevent lateral water movement in an insulation system, and used to separate different sections of a roofing system.

Dampproofing
Treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

Dead Level
Refers to a roof with no slope or pitch.

Dead Loads
Permanent, non-moving loads on a roof resulting from the weight of a building’s components, equipment, and the roof system.

Dead-Level Asphalt
A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type I. This asphalt is for use in roofs which do not exceed a ¼ in 12 slope (2%).

Deck
The structural component of the roof of a building which provides the substrate to which the roofing system is applied.

Decking
See Deck

Deflection
The downward displacement of a structural member under load.

Degradation
A decline in the appearance, structure, or properties, of a material or substance.

Delamination
Separation of laminated layers of a material or system.

Dew Point Temperature
The temperature at which water vapor turns to liquid in cooling air at the existing atmospheric pressure and vapor content.

Diaphragm
A type of structural roof deck capable of resisting shear that is produced by lateral forces such as wind or seismic loads.

Diffusion
The movement of a substance such as water vapor from regions of high concentration to regions of lower concentration.

Dimensional Shingle
A shingle that is textured, or laminated to produce a three-dimensional effect. Also known as Laminated and Architectural Shingles. Please be aware that there are also shingles being produced that can be classified as Dimensional but not as Laminated. These shingles are comprised of a single piece of material rather than two different materials laminated together.

Dimensional Stability
The ability of a material to retain its current properties and to resist a change in size resulting from exposure to temperature changes and moisture.

Dome
A roof with a partial-spherical shape.

Dormer
A framed projection through the sloping plane of a roof.

Double Coverage
Installing roofing so that there is twice the materials used resulting in a double layer of roofing.

Double Graveling
Installing one layer of gravel in a flood coat of hot bitumen, removing the excess gravel and then installing a second layer of gravel in another flood coat of hot bitumen.

Downspout
A conduit for carrying water from a gutter, scupper, drop outlet or other drainage unit from roof to ground level. Also known as a Leader Pipe.

Drain
A device used to carry water off of a roof.

Drip Edge
A steel flashing bent at a 90º angle that is placed along the outer perimeter of steep sloped buildings; used to help direct runoff water away from the building. Drip Edge resembles nosing except that it has an outwardly-angled bottom edge (preferably hemmed).

Drip Edge
A steel flashing bent at a 90º angle that is placed along the outer perimeter of steep sloped buildings; used to help direct runoff water away from the building. Drip Edge resembles nosing except that it has an outwardly-angled bottom edge (preferably hemmed).

Dry Bulb Temperature
The temperature of air in degrees Fahrenheit measured by an ordinary thermometer.

Dry Film Thickness
The thickness in mils (thousandths of an inch), of a dried coating or mastic.

Dry Rot
Wood rot caused by certain fungi. Dry rot can result from condensation build-up, roof leaks that go untended, or from other problems. Dry rot will not remain localized. It can spread and damage any lumber touching the affected area.

Dry-In
(1) The process of installing the underlayment in steep slope roofing; (2) Making a low-slope roof watertight. Does not always mean getting all of the required plies installed.

Dual Level Drain
An item that will permit drainage at two different levels.

Dynamic Load
Any moving load on a roof such as people and equipment. Wind can also be considered a Dynamic Load.

Eave
A roof edge that extends out past the exterior wall line.

Eaves-Trough
Another name for Gutter.

ECH
Polyepichlorohydrin. See also Epichlorohydrin.

Edge Stripping
Roofing material used to seal perimeter edge metal and the roof itself.

Edge Venting
The installation of vent material along a roof edge (e.g., Starter Vent) as part of a ventilation system. Edge vent material should be used in conjunction with other venting material (e.g., ridge vent) as it not intended for use by itself.

Elastomer
A material which, after being stretched, will return to its original shape.

Elastomeric
Properties of a material that will permit it to return to its original shape after being stretched.

Elastomeric Coating
A coating that can be stretched to twice its dimensions and that will return to original when tension is released.

Elongation
The ability of a material to be stretched or lengthened.

Embedment
In roofing, to uniformly press one material into another, such as aggregate into bitumen, roofing felt into bitumen, or granules into a coating.

Emulsion
Fine particles suspended in a liquid solution. See also Asphalt Emulsion and Bituminous Emulsion.

End Lap
The extension of one component of material past the end of an adjacent piece of material.

Envelope
A continuous seal for preventing bitumen from leaking down into or off a building. Is constructed by extending the base sheet or other non-porous ply of felt beyond the edge of the field plies. It is then turned back onto the top of the system and adhered. See also Bitumen-Stop.

EPDM
Ethylene Propylene Diene Monomer.

Epichlorohydrin (ECH)
A synthetic rubber material similar to EPDM with a stronger resistance to animal fats and oils than EPDM.

Epoxy
A type of synthetic, thermosetting resins that produce tough, hard, chemical-resistant coatings and adhesives.

Equipment Screen
A nonstructural wall or screen constructed around rooftop equipment such as HVAC units, curbs, etc. to hide the look of the equipment and make the structure more aesthetically pleasing.

Equiviscious Temperature (EVT)
The temperature at which a bitumen attains the proper viscosity for use in built-up roofing. There is usually a twenty-five degree Fahrenheit (25° F) variance permitted above and below the recommended EVT. The EVT is measured in application equipment just prior to application using a standard thermometer or it can be measured just after application using a laser thermometer.

Ethylene Propylene Diene Monomer (EPDM)
A thermoplastic rubber with high tear strength that can be cross-linked by both peroxides and sulfur.

EVT
Equiviscous Temperature

Exhaust Vent
A device used to vent air from the roof cavity with vents that are installed on or near the higher portions of the roof such as the ridge.

Expansion Cleat
A cleat designed to handle thermal movement of the metal roof panels.

Exposed-Nail Method
A method of installing roll roofing materials to where all nails/fasteners are visible and exposed to the elements.

Exposure
The portion of the membrane that is not overlapped by the succeeding ply or course. Or, the portion of the roofing material exposed to the weather after being installed.

Extrusion
The process of manufacturing and/or shaping a material by forcing it through a die.

Eyebrow
A small, shed roof protruding from the main roof or located on the side of a building below the level of the main roof.

Factory Mutual Research Corporation (FMRC)
As it relates to roofing – a division of Factory Mutual System that tests and classifies roof components and systems for their resistance to fire, traffic, impact, weathering, and wind-uplift. The various organizations of Factory Mutual are owned or directed by Allendale Insurance, Arkwright, and Protection Mutual Insurance.

Factory Seam
A splice/seam made in the roofing material by the manufacturer. It is preferable during installation to cut these splices out of the membrane.

Fading
Losing brightness or brilliance; dim.

Fallback
A reduction in the softening point temperature of asphalt that occurs when asphalt is overheated for pro-longed periods of time. See also Softening Point Drift.

Fascia
Vertical roof trim located along the perimeter of a building, usually below the roof level. Its use can be either decorative or for waterproofing.

Fasteners
Devices used to secure roof system components.

Feathering Strips
Strips of wood that are placed along the butt ends of wood shingles to form a somewhat smooth surface so that the shingles can be roofed over without removal.

Felt
A roofing sheet made of interwoven fibers. The fibers can be wood or vegetable for Organic Felts, glass fibers for fiberglass felts, polyester, or synthetic.

Felt Machine
A machine that will install bitumen and felt at the same time.

Ferrule
A metal sleeve used as a spacer to keep gutter from being beat up when secured to fascia with spikes.

Fiberglass Insulation
Insulation composed of glass fibers used to insulate walls and roofs. It can be rigid board or blanket insulation.

Field of the Roof
Refers to the central part of a roof away from the perimeter.

Field Seam
A non-factory material seam made by joining overlapping seams together with adhesives, heat welders, or other means.

Filler
An inert ingredient added to roofing materials in order to alter their physical characteristics.

Fillet
A sealant material installed at horizontal and vertical planes to remove 90° angles.

Film
A membrane or sheeting material with a nominal thickness of 10 mils or less.

Film Thickness
The thickness of a membrane or coating that is expressed in mils (thousandths of an inch). See also Wet Film Thickness and Dry Film Thickness.

Fin
A sharp protrusion in a roof deck that can damage roof components.

Fine Mineral-Surfacing
A fine mineral material on the surface of roofing materials to prevent them from sticking to surfaces. 50% of this material has to pass through a sieve with holes that are 1/35″ in size (#35 sieve).

Fishmouth
An opening along the exposed edge of an installed ply of felt caused by shifting the ply during installation. Repair these by making a slice along their entire length and feathering two plies of felt over the fishmouth for a minimum coverage of one foot all the way around.

Flaking
Occurs when a coating loses its cohesion.

Flame Retardant
A substance used to impede a material’s tendency to burn or ignite.

Flame Spread
A measure of relative combustibility. The flame spread of a tested material is rated relative to asbestos cement board (flame spread = 0) and red oak flooring (flame spread = 100).

Flammability
The ability of a material to burn or ignite.

Flange
A projection edge of a roof component such as flashings, skylight frames, pre-manufactured curbs, etc. Usually refers to the part that sits on the roof surface.

Flash
v. To install flashing components.

Flash Point
The lowest temperature of a liquid material at which combustion will occur when air reaches its surface.

Flashing
Components used to seal the roof system at areas where the roof covering is interrupted or terminated. For example, pipes, curbs, walls, etc. all have special components that, when correctly installed, will help prevent moisture entry into the roof system or building.

Flashing Cement
A trowelable mixture of solvent-based bitumen and mineral stabilizers. Flashing cement that may contain asbestos stabilizers is categorized by ASTM standard D 2822-91 (1997) or for non-asbestos, ASTM standard D 4586-93. Flashing Cement is the term for Asphalt Roof Cement that can be used on vertical surfaces and has a high softening point, low ductility and conforms to the requirement of ASTM Specification D 312, Types II or III; or Specification D 449, Type III. See also Asphalt Roof Cement and Plastic Cement.

Flashing Collar
A flashing component used to seal soil pipe vents, hot stacks or other roof penetrations.

Flat Lock
A type of interlocking two separate metal panels by folding one panel over on top itself and the folding the other down under itself and then hooking the panels together.

Fleece
Mats or felts used as a membrane backer and composed of fibers.

Flood Coat
The surfacing layer of bitumen into which aggregate is embedded on an aggregate-surfaced built-up roof. A flood coat is applied at an approximate rate of 45 to 60 pounds per square (100 square feet).

Flood Test
A water test performed to determine the effectiveness of a roof covering.

Flow
To become fluid in character.

Fluid-Applied Elastomer
A liquid elastomeric material that cures to form a continuous waterproofing membrane.

FM
Short for Factory Mutual Research Corporation

Foam Stop
The edge metal used to terminate Sprayed Polyurethane Foam

Framed Opening
An structurally-framed opening in a roof of a building for use in installing large items such as HVAC units, skylights, or ventilators.

Froth Pack
A term used to describe small, disposable aerosol cans of SPF.

G-90
A coating weight for galvanized sheet metal, 0.90 ounces of zinc per sq. ft., measured on both sides of the sheet.

Gable
A triangular-shaped portion of the endwall of a building directly under the sloping roof and above the Eave line.

Gable
A triangular-shaped portion of the endwall of a building directly under the sloping roof and above the Eave line.

Gable Roof
A roof configuration that has gable ends.

Gable-On-Hip Roof
A roof configuration with hips coming up from the eave corners that terminate into a gable roof.

Galvalume
Trade name for a protective coating composed of aluminum zinc.

Galvanic Action
A reaction between different metals in the presence of an electrolyte.

Galvanize
To coat with zinc.

Galvanized Steel
Steel that is coated with zinc to aid in corrosion resistance. Galvanized steel for use in roofing should be Hot-Dipped Galvanized with a G-90 coating.

Gambrel
A roof that has two different pitches.

Gauge
A standard of measurement. For instance the thickness of sheet metal or the diameter of wire. The thicker the wire or metal, the lower the gauge.

Geodesic Dome
A geodesic dome uses a pattern of self-bracing triangles in a pattern that gives maximum structural advantage, thus theoretically using the least material possible. (A “geodesic” line on a sphere is the shortest distance between any two points.) The first contemporary geodesic dome on record was designed by Walter Bauersfeld.

Girt
A horizontal beam place between support columns that is used for attaching wall cladding.

Glass Felt
(1)In the manufacturing of roofing materials – a sheet comprised of bonded glass fibers prior to being saturated with bitumen; (2) short for asphalt or coal tar saturated fiberglass felt membrane.

Glaze Coat
(1) The uppermost layer of asphalt on a smooth-surfaced built-up roof membrane, usually a reflective surfacing is installed over it; (2) A thin coat of bitumen applied to help protect the roof membrane when application of additional felts or the flood coat and aggregate surfacing are delayed.

Grain
A unit of measure for the mass of moisture: a unit of weight equal to 0.002285 ounces or 0.036 dram.

Granule
A small aggregate, naturally or synthetically colored, used to surface cap sheets, shingles, and other granule-surfaced roof coverings.

Gravel
Aggregate consisting of rock fragments or pebbles.

Gravel Stop
A flanged, sheet metal edge flashing with an upward projection installed along the perimeter of a roof to stop the flow of bitumen over the edge.

Grout
A thin mortar used to fill cracks in masonry and tile.

Grout (Non-Shrink)
A cementitious material used to partially fill penetration pockets (pitch pans). A pourable sealer is used afterward.

Gutter
A channel (usually sheet metal) installed along the downslope perimeter of a roof to convey runoff water from the roof to the drain leaders or downspouts.

Half Gable Roof
Half Gable Roof is a hybrid of a gable and a hipped roof. For more information about half gable roof please see Shed Roof.

Hand-Tabbing
Applying spots of adhesive to shingle tabs.

Hatch
A unit used to provide access to a roof from the interior of a building.

Headlap
The distance that the topmost ply of roofing felt overlaps the undermost ply or course.

Heat Seaming
See Heat Welding.

Heat Transfer
Thermal energy going from an area of higher temperature to an area of lower temperature by conduction, convection, or radiation.

Heat Welding
Fusing the seams of separate sections of roofing material together through the use of hot air or an open flame and pressure. Also known as heat seaming.

Hem
The edge created by folding metal back on itself. Metal is hemmed for safety and strength reasons.

Hip
The angle formed by the intersection of two sloping roof planes.

Hip
The angle formed by the intersection of two sloping roof planes.

Hip Roof
A roof that rises by inclined planes on all sides of a building. The line where two adjacent sloping sides of a roof meet is called the Hip.

Hoist
A mechanical lifting device. A hoist can be hand or electrically operated.

Holiday
An area where a liquid-applied material is missing.

Honeycomb
Voids left in concrete because the mortar failed to fill the spaces around the aggregate.

Hot
Slang for hot bitumen.

Humidity
The amount of water vapor in the air.

HVAC
Acronym for Heating, Ventilating, and Air Conditioning.

Hypalon
The trademark name for Chlorosulfonated Polyethylene (CSPE), which is a single-ply roofing material.

ICBO
International Conference of Building Officials, responsible for The Uniform Building Code.

Ice Dam
Ice formed at the transition from a warm surface to a cold surface, such as along the overhang of a house. The build-up of ice is the result of ice or snow melting on the roof area over the warmer, living area of a building and then refreezing when it runs down and reaches the overhang.

Ignition Temperature
The minimum temperature at which a material will combust.

Impact Resistance
A roof assembly’s ability to withstand the impact from falling objects such as hail.

Impregnate
To saturate; in roofing, asphalt impregnated fiber glass roofing felts are fiber glass mats that have been completely permeated with asphalt bitumen.

Infrared Thermography
The use of an infrared camera to detect moisture in roof insulation.

Inorganic
Involving neither organic life nor the products of organic life; relating to compounds not containing hydrocarbon groups.

Insect Screen
Material used to inhibit an insects ability to enter a building through openings in a roof such as vents.

Insulation
Material used to help maintain a certain temperature in a building by reducing the flow of heat to and from that building. See also Thermal Insulation.

Intake Ventilation
The part of a ventilation system used to draw fresh air in. Usually vents installed in the soffit or along the eaves of a building.

Interlayment
A waterproof material usually installed between adjacent rows of wood shakes to help with the roof’s waterproofing characteristics.

Interlocking Shingles
Shingles that lock together to provide wind resistance. See also T-Lock.

Internal Pressure
Atmospheric pressure inside a structure that correlates to the number and location of openings and air leaks.

Inverted Roof Membrane Assembly (IRMA®)
A variation of the “Protected Membrane Roof Assembly” in which Styrofoam® brand insulation is used. IRMA® and Styrofoam® are registered trademarks of the Dow Chemical Company.

IRWC
Institute of Roofing and Waterproofing Consultants

ISANTA
International Staple, Nail & Tool Association

Isocyanate
A highly reactive organic chemical containing one or more Isocyanate groups. A basic component in Sprayed Polyurethane Foam systems and some polyurethane coating systems.

Jack
See Roof Jack.

Joint Tape
Tape used to seal joints between insulation boards.

Joist
Any of the parallel horizontal beams set from wall to wall to support the boards of a floor, ceiling or roof of a building.

Knee Cap
Sheet metal trim that fits over a panel rib after it has been cut and bent.

Laitance
An accumulation of fine, powdery aggregate particles on fresh cement caused by the upward movement of water; indicates that too much water was used in the mix resulting in poor surface adhesion for a waterproofing layer.

Laminated Shingles
See Dimensional Shingles or Architectural Shingles.

Lap
The part of the roofing material that overlaps a section of adjacent material.

Lap Cement
Asphalt-based roof cement used to adhere overlapping plies of asphalt roll roofing.

Lap Seam
Where two material that overlap are sealed together.

Lead
Metal used for flashing material.

Leader Head
A component used to direct water from a through-wall scupper to a downspout. Also known as a Collector Head.

Leader Pipe
A conduit for carrying water from a gutter, scupper, drop outlet or other drainage unit from roof to ground level. Also known as Downspout.

Lift
The rise in Sprayed Polyurethane Foam resulting from a pass.

Live Loads
Temporary items on a roof such as equipment, people, snow, etc. which the roof must be designed to support.

Loose-Laid Roof Membranes
Roofing material attached only at the perimeter and at penetrations and held in place by ballast, pavers, or other materials.

Mansard
(1) A steep-sloped roof located at the perimeter of a building and usually used for decorative purposes. (2) The upper story formed by the lower slope of a mansard roof.

Mansard Roof
A steeper roof that terminates into a lower sloped roof at its high point.

Masonry
Refers to bricks, concrete, or concrete blocks.

Mastic
See Asphalt Roof Cement.

Mat
A thin layer of woven, non-woven, or knitted fiber used to reinforce a material.

Material Safety Data Sheets (MSDS)
Written descriptions of the chemicals in a product provided by the product’s manufacturer. MSDS also contain other information such as emergency procedures and safe handling.

MBMA
Metal Building Manufacturers Association

MCA
Metal Construction Association

Mechanical Damage
Damage to a roof by means of items puncturing or otherwise unnecessarily penetrating the roof system or any of its components. Screws or nails stuck in the roof and heel marks along base flashings are examples of mechanical damage.

Mechanical Fasteners
Devices such as screws, plates, battens, nails, or other materials that are used to secure roofing materials.

Membrane
The portion of the roofing system that serves as the waterproofing material. Can be composed of one material or several materials laminated together.

Metal Flashing
Roof components made from sheet metal that are used to terminate the roofing membrane or material along roof edges. Metal flashings are also used in the field of the roof around penetrations.

Meter
Metric unit of length measurement equal to 39.37 inches.

Mil
A unit of measure equal to 0.001 inches (1/1000 in.) used to indicate the thickness of a roofing membrane.

Mildew
A superficial coating or discoloration of organic materials caused by fungi, especially under damp conditions.

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

MIMA
Mineral Insulation Manufacturers Association

Mineral Fiber
Inorganic fibers of glass or rock.

Mineral Granules
See Granules.

Mineral-Surfaced Roofing
Roofing materials with a top surface consisting of mineral granules.

Miter
The joint made by two diagonally cut pieces put together.

Model Codes
A group of codes and standards accepted by more than one of the Building Code regulatory agencies such as SBCCI, BOCA, and ICBO

Modified Bitumen
A bitumen modified by one or more polymers such as Atactic Polypropylene (APP), styrene butadiene styrene (SBS).

Moisture Relief Vent
A vent installed through the roofing membrane to relieve moisture vapor pressure that has been trapped within the roofing system.

Moisture Scan
A survey of a roof specifically to detect the amount of moisture present in the roof system. Devices used in moisture surveys can be capacitance meters, infrared cameras, and nuclear scanners. Infrared scans can be done from the air or on the surface of the roof. Capacitance and nuclear scans are done on the roof surface. It is argued that the most accurate scans are done from the surface of the roof with the most accurate of these being nuclear scans.

Mole Run
A term used to describe a ridge in a roof membrane that is not the result of improper deck or insulation joints.

Monolithic
Used to describe something without seams; formed from a single material.

Monomer
A simple molecule that can combine with other to form a polymer.

Mop-and-Flop
A roofers’ term where the back side of a roofing material is mopped, then the piece is turned over and set in place.

Mopping
To apply hot asphalt or coat tar using a hand mop or mechanical applicator.

Mud Cracking
Surface cracking of a material that looks similar to dried, cracked mud.

Multiple Coats
More than one layer of coating applied to a substrate.

NAHB
National Association of Home Builders

Nailer
A piece of lumber, preferably treated, that is secured to the deck, walls, or to premanufactured curbs. Nailers are used to receive fasteners for roof membranes. Generally, nailers are installed wherever it is necessary to secure base flashings and edge metal. Also see Blocking.

Nailing Pattern
Refers to a specific method or pattern at which nails are applied. For instance, a nailing pattern for base sheets on plywood roof decks can be “Nine and Eighteen”. This means one row of nails on the outside edge of the sheet set at nine inches (9″) on center, and two rows in the center of the sheet, each set at eighteen inches (18″) on center.

Neoprene
A synthetic rubber produced by polymerization of Chloroprene for use in liquid-applied and sheet-applied elastomeric roofing.

Nesting
To overlay existing shingles with new shingles and butt the top edge of the new shingle up against the bottom edge of the existing shingles.

Net Free Vent Area
The area permitting unrestricted air flow.

Newton (N)
In the meter-kilogram-second system, the unit of force required to accelerate a mass of one kilogram one meter per second per second (s².)

NICA
National Insulation Contractors Association

Night Seal
To temporarily seal the edge of a roof membrane in order to protect it from moisture entry. A.K.A. Night Tie-Off and Water Cut-Off.

NIST
National Institute of Standards and Technology

No-Cutout Shingle
A shingle made of one solid strip of material.

Noble
In reference to metal, inert or inactive.

Non-Breathing Membrane
A membrane that does not permit water vapor or air to permeate it.

Non-Flammable
Material with no measurable flash point.

Non-Friable
Refers to a material’s inability to be crushed or pulverized into a powder.

Non-Volatile Content
The portion of a material that will not evaporate.

Non-Vulcanized Material
A material that retains its thermoplastic properties throughout its service life.

Non-woven
Random arrangement of the reinforcement fibers of a scrim sheet or mat.

Nosing
Metal flashing bent at a 90º angle and is installed around roof perimeters, curbs, platforms, etc. in order to protect the edge of the roofing system. Nosing should not be used in place of drip edge. To see the difference in the two, click here.

NRCA
National Roofing Contractors Association.

NTRMA
National Tile Roofing Manufacturers Association.

Off-Ratio Foam
SPF where the 1 to 1 ratio of the A and B components has been compromised and which results in a lower quality material.

Open Time
The time after an adhesive has been applied and permitted to cure when the two surfaces can be bonded.

Open Valley
A valley where both sides of the roof are trimmed back from the centerline to expose the valley flashing material beneath.

Orange Peel Surface Texture
A surface with a texture comparable to the skin of an orange upon which a protective coating may be applied.

Organic
Formed from hydrocarbons.

Organic Felt
An asphalt roofing base material manufactured from cellulose fibers.

Organic Shingle
An asphalt shingle reinforced with organic material manufactured from cellulose fibers.

ORNL
Oak Ridge National Laboratory

OSB
Oriented Strand Board – Often used as roof sheathing in place of plywood.

Overlay
See Re-Cover.

Overspray
The loss of spray particles (from coatings, SPF, etc.) in the air.

Pallet
A platform used to hold materials.

Pan
(1) The concave piece of “Pan and Cover” tile whose rounded surface touches the top side of the roof substrate. (2) The flat part of a roofing panel located between the ribs.

Pan Flashing
A sheet metal flashing that covers an equipment platform and is designed to counter flash the base flashings surrounding the platform.

Parapet Wall
That part of a perimeter wall that extends above the surface of the roof.

Pass
The term used to describe the application of one layer of Spray Polyurethane Foam (SPF). The speed of a pass will determine foam thickness.

Pass Line
The distinct line formed between two passes of SPF. This line is the top skin of the bottom pass of the SPF.

Penetration
Any object that pierces the surface of the roof.

Percent Elongation
The maximum amount that a material can be lengthened or stretched before breaking; expressed as a percentage of the original length of material tested.

Perlite
A natural volcanic glass having distinctive concentric cracks and a relatively high water content.. Perlite in a fluffy heat expanded form is used in lightweight insulating concrete, fire-resistant rigid insulation board (R = 2.78 per inch) and potting soil.

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

Permeability
The rate of flow of a liquid or gas through a porous material.

pH
A measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.

Phasing
Installing roof system components in separate time intervals. For instance, installing a base sheet, and then two plies of roofing one day, and coming back and installing the remaining two plies one or more days later. It is generally not considered Phasing if the surfacing is applied at a later date.

Picture Framing
Rectangular patterns seen in a roof that are created by buckles or ridges in the roof system or sumps in the substrate.

PIMA
Polyisocyanurate Insulation Manufacturers Association

Pinhole
A small hole in a coating, foil, membrane, or other roofing material.

Pipe Boot
A prefabricated flashing piece used to flash around circular pipe penetrations. Also known as a Roof Jack. Click here for an example.

Pitch
Term used to describe Roof Slope and also short for Coal Tar Pitch.

Pitch Pocket (a.k.a. Pitch Pan)
A flanged piece of flashing material placed around irregularly shaped roof penetrations and filled with grout and a pourable sealer to seal around the penetration in order to seal it from against moisture entry. Pitch pockets are a good source of leaks and should be avoided if possible.

Pittsburgh Lock Seam
The common type of longitudinal seam is the Pittsburgh Lock Seam. To put it in simple, Pittsburgh Lock Seam is a method of interlocking two separate pieces of metal.

Plastic Cement
A term used to describe Type I asphalt roof cement. Plastic cement should not be used on vertical surfaces. See also Asphalt Roof Cement and Flashing Cement.

Plastic Film
A flexible sheet made by the extrusion of thermoplastic resins.

Plasticizers
Material incorporated into rubber and plastic in order to increase their flexibility and workability.

Plenum
A space or enclosure in which air or other gas is at a pressure greater than that of the outside atmosphere.

Ply
A layer of felt or other reinforcement material in a roof system.

PMR
See Protected Membrane Roof.

Polyester
Any of numerous synthetic polymers produced chiefly by reaction of dibasic acids with Dihydric alcohols and used primarily as light, strong, weather-resistant resins. In roofing, polyester is used to reinforce fabrics.

Polymer
Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule.

Polymer Modified Bitumen
See Modified Bitumen.

Polymeric Methylene Diphenyl Diisocyanate (PMDI)
The “A” component in SPF; when mixed with “B”, it forms polyurethane. PMDI is an organic chemical compound having two reactive Isocyanate (-N=C=O) groups.

Polymerization
The combining of monomers to produce polymers.

Polypropylene
Any of various thermoplastic resins that are polymers of propylene. They are hard and tough, and are used to make molded articles and fibers.

Polyvinyl Chloride (PVC)
A thermoplastic polymer that can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, fillers, and other modifiers; rigid forms are used in pipes; flexible forms are used in the manufacture of sheeting and roof membrane materials.

Ponding
The accumulation of water at low-lying areas on a roof.

Pop Rivet
A small metal pin having a head on one end, inserted through aligned holes in pieces of light gauge metal to be joined and then the head is expanded to join the metal.

Popcorn Surface Texture
A coarse surface texture of SPF considered unacceptable for coatings.

Positive Drainage
The drainage condition of a roof where all water is gone from the roof surface within forty-eight hours of precipitation during normal drying conditions.

Pot Life
The period of time during which a material with multiple ingredients can be applied or administered after being mixed together.

Pourable Sealer
A type of sealant that is initially in liquid form commonly used in conjunction with pitch pans to form a water-tight barrier around penetrations that are difficult to flash.

Press Brake
A mechanical device used to form sheet metal into desired shapes and profiles.

Primer
A material that is applied to a surface in order to increase that surface’s ability to adhere to or work in conjunction with a subsequently applied material.

Proportioner
A pumping unit comprised of two (2) positive displacement pumps that is designed to dispense two (2) components at a precise ratio. Used in SPF and plural component coating applications.

Protected Membrane Roof (PMR)
A roof assembly in which the insulation and ballast are placed on top of the membrane component. Commonly referred to as an “inverted roof assembly.”

Psychrometer
An instrument that uses the difference in readings between two thermometers, one having a wet bulb and the other having a dry bulb, to measure the moisture content or relative humidity of air.

Puncture Resistance
The ability of a material to withstand being pierced by a sharp object.

Purlin
Horizontal secondary structural member used to transfer loads from the primary structural members.

PVC
See Polyvinyl Chloride.

R-Value
The measure of a material’s resistance to heat flow. The higher a material’s R-value, the more it insulates.

Racking
The method of installing asphalt shingles where the shingles are installed straight up to the ridge rather than horizontally. If this method is used with 3-tab shingles, the throats of every other course will line up.

Rafter
The structural member extending from the downslope perimeter of a roof to the ridge or hip and is designed to support the roof deck and roof system components.

Raggle
A groove that is cut into the side of a vertical surface such as a wall or chimney that is used to insert a flashing element such as a reglet or counterflashing.

Rake Edge
The sloped perimeter edge of a roof that runs from the eaves to the ridge. The rake is usually perpendicular to the eaves and ridge.

Rake-Starter
A starter strip placed along rake edges for use in asphalt shingle roofing. See also Bleeder Strip.

RCDA
Roof Deck Contractors Association

RCI
Roof Consultants Institute

RCMA
Roof Coatings Manufacturers Association

Re-Cover (Overlay)
The installation of a new roof system over an existing system without removing an existing system.

Re-roofing
The procedure of installing a new roof system.

Reglet
A receiver, usually sheet metal, that counterflashings are attached to. Reglets can be surface-mounted, set in a raggle, or be part of the wall assembly.

Reinforced Membrane
A roofing membrane that has been strengthened by adding polyester scrims or mats, glass fibers or other material.

Relative Humidity
The amount of water vapor in the air compared to the amount of water vapor that the air can hold at a given temperature. For example, if the relative humidity is 50 percent, then the amount of water vapor in the air is half of what the air could actually hold at that temperature.

Remove and Reinstall
To remove a component and reuse that component by reinstalling it.

Remove and Replace
To remove a component and replace it with a new component of the same or similar type.

Resin
The “B” component in SPF that is mixed with the “A” component in order to form polyurethane. Resin contains a catalyst, fire retardants, a blowing agent, Polyol, and a surface active agent.

Ridge
The line where two planes of roof intersect, forming the highest point on the roof that runs the entire length of the roof.

Ridge Cap
Material applied over the ridge or hip of a roof.

Ridge Course
The final course of roofing applied that covers the area where two or more roof planes intersect.

Ridge Vent
An exhaust venting device located at the ridge of a roof that works in conjunction with a starter or under eave soffit vent and is used to ventilate attics. Ridge vents and their cooperative starter or soffit vents should be installed at a 1:1 ratio in order to function properly.

Ridging
The formation of a Buckle.

RIEI
Roofing Industry Educational Institute

RMA
Rubber Manufacturers Association

Roll Goods
The term used for all roofing materials that come in rolls.

Roof Assembly
A term used to describe all of the roof components including structural roof deck.

Roof Cement
See Asphalt Roof Cement and Coal Tar Roof Cement.

Roof Covering
The outermost reinforced layer of the roof assembly. In BUR it’s the multiple-ply membrane, in Thermoplastic roof systems it’s the thermoplastic sheet, etc.

Roof Curb
A frame used to structurally mount rooftop equipment such as HVAC units, exhaust fans, skylight, etc.; may be pre-constructed or constructed on site.

Roof Jack
(1) A steel bracket fastened to the roof that is used to support toe boards. (2) A term used to describe a Pipe Boot or Flashing Collar.

Roof Overhang
That portion of the roof that extends beyond the exterior wall line of the building.

Roof Seamer
(1) A mechanical device used to crimp metal roof panels and make the seams watertight. (2) A machine used to weld membrane laps of PVC (Thermoplastic) roofing material.

Roof Slope
The angle made by the roof surface plane with the horizontal plane and expressed as the amount of vertical rise for every twelve inch (12″) horizontal run. For instance, a roof that rises four inches (4″) for every twelve inch (12″) horizontal run, is expressed as having a “four in twelve” slope; often written as “4:12.” Expressed as a percentage, the slope would be 33%, which is equal to 4 divided by 12. Also known as the Pitch of a roof.

Roof System
Multiple roof components assembled to provide waterproofing (and sometimes insulating) capabilities for a structure.

Roofer
An individual who installs roof systems and materials.

Rosin
Non-asphaltic material used as slip sheets and sheathing paper in roof systems. Also referred to Rosin Paper and Rosin-Sized Sheathing Paper.

Run
The horizontal dimension of a slope.

Rust Blush
Early stage of rust indicated by an orange or reddish color.

Saddle
(1) A type of flashing usually used in conjunction with step, counter, and apron flashings on steep slope roof systems. (2) A small, somewhat pyramid-shaped figure constructed in between sump drains that is used to direct run-off water toward the sump drains.

Sag
Settling or drooping of base flashings that have not been properly secured to a surface.

Saturated Felt
Felt that has been saturated with bitumen.

SBCCI
Southern Building Code Congress International, Inc.

SBS
Styrene Butadiene Styrene.

Scarfed
Shaped by grinding.

Screeding
Bringing the surface of concrete to the final, desired look and finish by removing any excess or unwanted material.

Screen or Screen Wall
See Equipment Screen.

Scrim
Woven or non-woven material used to reinforce membranes; it is usually laminated or coated to produce the membrane.

Scuttle
A unit that provides access to the roof from the interior of the building. See also Hatch.

SDI
Steel Deck Institute

Sealant
Generic term for a multitude of materials used to seal joints or junctures against moisture or weather.

Sealer
Coating designed to prevent bleed-out or bleed-through.

Seam
A line, ridge, or groove formed from fitting, joining, or lapping two sections together.

Self-Adhering Membrane
A type of membrane whose bottom surface will stick or adhere to a substrate without the use of an additional adhesive material.

Self-Drilling Screw
A screw with a small drill-bit like tip that will drill its own hole and eliminate the need to pre-drill a hole.

Self-Sealing Shingle
Asphalt shingles with adhesive strips that will soften and stick to the following course of shingles when heated by the sun; used to help against wind uplift.

Self-Tapping Screws
Fasteners that make screw thread receivers when screwed into a hole.

Self-Vulcanizing Membrane
Membrane that is initially thermoplastic in nature but that cures after installation.

Selvage Edge
That portion of a granule-surfaced membrane that is designed to be overlapped by the following membrane course; usually two, four, or nineteen inches in width.

Shark Fin
A curled corner or lap in a membrane.

Shed Roof
A roof with only one sloping plane. Also known as Half Gable.

Shelf Life
The length of time between the manufacture of a material and when the material is no longer suitable for use.

Shiner
Term used to describe an exposed nail; one that was not covered by the following course of roofing material.

Shingle
(1) A single piece of prepared roofing material, either asphalt or wood, for use in steep slope roof systems. (2) To install a wood or asphalt shingle roof system.

Shingle Fashion
Refers to the way courses of like materials are overlapped in order to have multiple layer coverage.

Shrinkage
The process of shrinking; depreciation in size.

Shrinkage Crack
A crack caused by material shrinkage. May be the result of thermal expansion/contraction, material failure, or cure.

SI
The international system of weights and measures (metric system). Système International [d’Unites]

Side Lap
The longitudinal overlap of neighboring materials.

Siding
Exterior wall finish materials applied to the outside of a structure.

Sill
The bottom framing member of a door or window opening.

Sill Flashing
Flashing material(s) used to waterproof the bottom framing member of a door or window opening.

Single Coverage
One layer of roofing material.

Single-Lock Standing Seam
A standing seam system with one overlapping interlock between two seam panels.

Single-Ply Membranes
Roofing membranes that are applied in one layer. Thermoplastic and thermoset membranes are usually Single-Ply Membranes. Single-Ply membranes come in five basic types: (1) Ballasted, (2) Fully-Adhered, (3) Mechanically-Fastened, (4) Partially-Adhered, and (5) Self-Adhered. Seams of Single-Ply Membranes can be heat welded, solvent welded, and adhered using seam tape or other adhesives.

Single-Ply Roofing
Roofing systems where the principal component consists of a single-ply membrane.

Skylight
A transparent or translucent item that is designed to admit light and set over a curbed opening in the roof.

Slag
Residue from blast furnaces that is sometimes used for the surfacing on aggregate-surfaced built-up roof systems.

Slate
A fine-grained metamorphic rock that splits into thin, smooth-surfaced layers used in steep slope roofing applications.

Slating Hook
A hook-shaped device used to secure roofing slate.

Slip Sheet
Sheeting material placed between roofing components to prevent those components from adhering to one another or to prevent material damage due to component incompatibility. Slip Sheets may be polyethylene, rosin-sized sheathing paper, or other material.

Slit Sample
A cut made in SPF roofing to measure coating thickness. The cut should be about 1.5″ long by ¾” deep by ½” wide.

Slope
The angle of incline of a roof expressed as a percent or as a ratio of rise to run. See Roof Slope.

SMACNA
Sheet Metal and Air Conditioning Contractors National Association

Smooth Surface Texture
In SPF roofing, a relatively smooth surfaced texture that is considered ideal for receiving the base coating.

Smooth Surfaced Roof
A roof with no surfacing or with a smooth surfacing such as emulsion and/or a reflective coating.

Snow Guard
Devices secured to the roof to prevent snow and ice from sliding off of a roof.

Snow Load
A roof load resulting from snowfall. Snow load is a major structural consideration when roofs are designed in areas that receive heavy snow.

Soffit
The underside of a roof overhang.

Soffit Vent
An intake ventilation device located in the soffit. An exhaust vent should be installed on or near the ridge of the roof to work in conjunction with the soffit vent in order to properly ventilate the attic space. The ratio of intake vent area to exhaust vent area should be 1:1.

Softening Point
The temperature at which bitumen will begin to Flow.

Softening Point Drift
A change in the softening point of bitumen. See also Fallback.

Soil Stack
A pipe that penetrates a roof and is used to vent a building’s plumbing.

Solder
Any of various fusible alloys, usually tin and lead, used to join metallic parts.

Solid Mopping
To continuously apply hot asphalt or coal tar leaving no areas without bitumen.

Solvent
(1) A liquid capable of dissolving other substances such as bitumen. (2) A liquid that is part of a substance and is used to make that substance easier to work with. Once applied, the solvent evaporates and leaves the working characteristics of the substance. Examples are solvent-based adhesives and solvent-based mastics.

Solvent Weld
To weld materials using a liquid solvent.

Spall
A chip, fragment, or flake from concrete or masonry.

Special Steep Asphalt
A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type IV. This asphalt can be used on roofs with slopes up to 6 in 12 (50%).

Specification
Written requirements for a construction project; contains but is not limited to the following: the scope of work, methods of construction, and materials.

SPF
Sprayed Polyurethane Foam.

SPF Compounds
Refers to the Isocyanate and resin components used to make polyurethane foam.

SPI
The Society of the Plastics Industry

SPI/SPFD
The Society of the Plastics Industry/Sprayed Polyurethane Foam Division

Splash Guard
A fabricated metal pan or masonry block that is placed below a leader pipe or downspout and is used to help protect the roof membrane on a lower roof level or to prevent soil erosion when placed on the ground.

Splice
To join by overlapping along ends.

Splice Plate
A metal plate placed beneath the joint between two pieces of metal.

Splice Tape
A self-adhering (usually double-sided) tape used for splicing membrane materials.

Split
The separation of a material resulting from tensile forces.

Sprayed Polyurethane Foam (SPF)
A monolithic sprayed-on roofing material with a high R-value; formed when isocyanate (“A” component) and resin (“B” component) are mixed at a 1:1 ratio.

SPRI
Single Ply Roofing Institute

Sprinkle Mopping
To scatter hot bitumen over a surface.

Spud
To remove the top surfacing of a roof by scraping it with special tools called spud bars or power spudders.

Spud Bar
A long-handle tool with a stiff flat blade on one end (usually 4″ or 6″ wide) that is used to scrape and remove the top surfacing of a roof down to the membrane.

Spunbond
Describes nonwoven fabrics made from continuously bonded fibers.

Spunlaced
Describes nonwoven fabrics that have the fibers intertwined by water-jet method.

Square
(1) 100 square feet of roof area (9.29 m2) in the USA. (2) 10 square meters (107.639 ft.2) of roof area using the metric system of weights and measures.

Stack Effect
The occurrence where air escapes through opening in the upper part of a building and is replaced with outside air which enters through an opening lower down. In roofing, the Stack Effect helps create proper air flow for attic or roofspace ventilation. The Stack Effect will be affected by atmospheric conditions such as temperature and wind.

Stainless Steel
A highly corrosion resistant steel alloy containing either chromium, nickel, or copper.

Stair Step
The diagonal method of laying shingles.

Standing Seam
A type of metal roof system where the longitudinal seams on adjacent panels are turned up, overlapped and folded in various ways in order to prevent moisture entry and interlock the panels.

Starter Course
The primary course of roofing materials. The Starter course is installed along the downslope perimeter edge and usually covered by the first course of roofing.

Starter Plies
Felt or ply sheets that are cut into widths that are proportionate to the reciprocal of the number of plies being installed. For instance, with a three-ply built-up roof, the first starter ply would be one-third of the roll width, the second two-thirds of the roll width installed over it, and then a full ply over those.

Starter Shingles
The first course of roofing installed. Sometimes trimmed from main roof material.

Starter Strip
Strips of shingles (usually 3-Tab shingles with the tabs cut off) or roll roofing material that is laid along the eave line of the roof prior to the application of the first course of shingles. The starter strip is used to fill in the gaps created by shingle cutouts and joints.

Static Load
Roof loads that do not move such as HVAC units.

Steep Asphalt
A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type III. This asphalt can be used on roofs with slopes up to 3 in 12 (25%).

Steep-Slope Roof
A roof with a slope exceeding 3 in 12 (25%). Deemed appropriate to receive water-shedding type roofing materials such as asphalt shingles, wood shakes and shingles, concrete or clay tile, etc.

Steep-Slope Roofing Materials
Roofing materials that depend on their water-shedding capabilities to keep moisture from entering a building. These materials are generally installed on roofs with slopes that equal or exceed 3″ in 12″ (25%).

Steeple
A tall tower forming the superstructure of a building, such as a church or temple, and usually surmounted by a spire.

Step Flashing
Pieces of metal or other material that are used to flash roof projections such as chimneys, walls, curbs, etc. The pieces are installed between each course of roofing and generally have a vertical flange equal in length to that of the horizontal flange.

Strapping
Installing roofing felts so that they run parallel with the slope. Not a recommended installation method for slopes that are 1:12 or less.

Straw Nail
Long-shanked nails used to fasten tile along hips and ridges.

Strawberry
See Tar Boil.

Strip Flashing
Pieces of membrane material that are used to flash metal flashing flanges such as gravel stop. Also referred to as Stripping.

Strip Mopping
Hot bitumen applied in parallel bands.

Strip Mopping
Asphalt shingles that are manufactured in strips.

Styrene
A colorless oily liquid, C6H5CH:CH2, the monomer for polystyrene.

Styrene Butadiene Styrene (SBS)
The modifying agent used in SBS modified asphalt roofing materials that gives the material a rubber like quality.

Substrate
The surface that the roof is installed upon.

Sump
A depression around roof drains and scuppers to help promote roof drainage.

Surface Erosion
The effect on a surface after being worn away from abrasion or weathering.

Surface Texture
The final appearance and quality of an SPF surface. SPF surface textures will be one of the following: Orange Peel Surface Texture, Coarse Orange Peel Surface Texture, Smooth Surface Texture, Verge of Popcorn Surface Texture, Popcorn Surface Texture, and Tree-Bark Surfaced Texture.

Surfacing
The top-most layer of the roof system designed to protect the system from damage.

Surfactant
Short for “surface active agent.” A soluble compound that reduces the surface tension of liquids, or reduces interfacial tension between two liquids or a liquid and a solid having cationic (positive charge), anionic (negative charge), or non-ionic (no charge) nature. The ingredient in SPF that controls the cell size.

SWRI
Sealant, Waterproofing and Restoration Institute.

Tab
The portion of an asphalt shingle that is outlined by the cutouts.

Tape
See Joint Tape and Splice Tape.

Tapered Edge Strip
Tapered insulation strip used to ease transitions from one substrate elevation to another and to provide slope along roof perimeters.

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.

Tar Boil
A small bubble found in the flood coat of an aggregate-surfaced built-up roof; usually the result of trapped moisture vapor. Tar Boils are also known as blueberries or blackberries.

Tear Resistance
A material’s ability to withstand tearing. The test is performed by placing stress on an area of the material where a flaw is located. Tear Resistance is expressed in PSI per inch width or kilo-newton per meter width.

Tear Strength
The strength necessary to tear a material.

Tear-off
To remove a roof system down to the structural substrate.

Tensile Strength
The amount of longitudinal pulling stress that a material can withstand before being pulled apart.

Termination
The sealed edges of a roof membrane.

Termination Bar
A bar, usually metal or vinyl, used to seal and anchor the free edges of a roof membrane.

Terne
Sheet iron or steel plated with an alloy of three or four parts of lead to one part of tin, used as a roofing material.

Terra Cotta
A semi-fired ceramic clay used in building construction.

Thatch Roof
A roof covering made with straw, palms, reeds or other natural growths that are bound together in order to shed water.

Thermal Barrier
Material used in conjunction with polyurethane foam that is designed to inhibit the rise in temperature of the foam during a fire in order to delay the foam’s involvement in the fire. Time ratings for thermal barriers should exceed 15 minutes.

Thermal Conductance ©
A constant, equal to a material’s k-value (Thermal Conductivity) divided by the material’s thickness in inches; used often for materials of composite construction such as insulation.

Thermal Conductivity (k)
The heat energy that will be transmitted by conduction through 1 square foot of 1inch thick homogeneous material in 1 hour when there is a difference of 1 degree Fahrenheit perpendicularly across the two surfaces of the material. The higher the k-value, the lower the R-value. Materials with high k-values are good heat conductors, and conversely.

Thermal Insulation
A material used to reduce heat flow.

Thermal Resistance®
The measure of a material’s ability to resist heat flow. The formula for Thermal Resistance is R = L / k where (L) is the material’s thickness and (k) is the material’s Thermal Conductivity constant. The higher a material’s R-value, the better it insulates, and conversely.

Thermal Shock
The damage to a roof resulting from expansion and contraction which are the result of sudden extreme temperature changes. Thermal Shock often occurs when a cold rain shower suddenly cools a roof during a hot day.

Thermal Stress
Stress to a roof system or component caused by expansion and / or contraction from temperature change.

Thermoplastic
(1) adjective Becoming soft when heated and hard when cooled. (2)noun A thermoplastic resin, such as polystyrene or polyethylene.

Thermoset
A material that cannot be reshaped or formed by heating. EPDM and Butyl are thermosets.

Thinners
Liquids that are used to reduce a material’s viscosity when mixed but that evaporates during cure.

Thixotropy
Property of certain materials which liquefy when they are subjected to vibratory forces such as simple stirring or shaking and then solidify when left standing.

Throat
(1) The cutout of a shingle. (2) The narrowing passage located between a fireplace and smoke chamber or flue.

Through-Wall Flashing
A material that extends through a wall and is used to direct water entering a wall cavity to the exterior of the structure.

Tie-In
The joining of two different roof systems.

Tie-Off
A watertight seal used to terminate roof membranes at system adjuncts, terminations, flashings, or substrates. Can be temporary (see Night Seal) or permanent.

TIMA
Thermal Insulation Manufacturers Association

Toggle Bolt
A bolt with a separate toggle end that can be flattened to fit through a pre-drilled hole and that springs outward to provide securement when the bolt is tightened.

Tongue-and-Groove
Pre-manufactured materials with a convex “tongue” on one side and a concave “groove” on the other so that pieces of material can be joined together by placing the tongue of one piece into the groove of an adjacent piece so that the pieces fit more securely together.

Torque
Force applied to an object, particularly, to screw a mechanical fastener into a roof deck or substrate.

TPA
Tri-Polymer Alloy.

Traffic
Any rooftop activity that can potentially damage the roof surface.

Tranverse Seam
The joint between the top of one metal roof panel and the bottom of the next panel, which runs perpendicular to the roof slope.

Treebark Surface Texture
An SPF surface deemed unacceptable for coating. This surface texture has deep valleys and is similar in appearance to rough tree bark.

Tuck Pointing
To remove old and deteriorated mortar from between masonry blocks and replace it with new mortar.

U-Valve
The overall coefficient of heat transfer of an assembly measured in BTUs per square foot, per degrees Fahrenheit difference in temperature per hour.

UBC
Uniform Building Code.

UL
Underwriters Laboratories, Inc.

UL Label
A label that has been stamped on certain materials by authority of Underwriters Laboratories, Inc. indicating that the material has met certain performance criteria.

Ultraviolet Light (UV)
A form of luminous energy occupying a position in the spectrum of sunlight beyond the violet, and having wavelengths that do not enter the visible spectrum. UV rays accelerate deterioration of roof materials. Hence, the need for protective coatings.

Underlayment
A material installed over the roof deck prior to the application of the primary roof covering. Usually consists of fifteen (15#) or thirty (30#) pound organic felt. Fiberglass reinforced and synthetic underlayments are becoming more popular due to their strength and moisture-control design.

Underlayment
A material installed over the roof deck prior to the application of the primary roof covering. Usually consists of fifteen (15#) or thirty (30#) pound organic felt. Fiberglass reinforced and synthetic underlayments are becoming more popular due to their strength and moisture-control design.

Underwriters Laboratories (UL)
A non-profit agency which functions as the testing arm of the National Board of Fire Underwriters. It maintains laboratories for the examination and testing of various devices, systems, and materials to determine their safety against the hazards of fire, wind, and accidents.

Uplift
See Wind Uplift.

Upside Down Roof
See Protected Membrane Roof

Valley
The internal intersection of two sloping roof planes that runs from the eaves to the ridge. This intersection collects the most water run-off. See Open Valley, Closed-Cut Valley, and Woven Valley.

Vapor Migration
The natural movement of water vapor from regions of higher vapor pressure to regions of lower vapor pressure.

Vapor Pressure
The pressure at which a liquid and its vapor are in equilibrium at a definite temperature.

Vapor Retarder
A material used to restrict the passage of water vapor through a roof assembly.

Veneer
Any of the thin layers of wood glued together to make plywood.

Vent
An opening or device used to permit air or vapors to exit an enclosed structure.

Vent Pipe
A vertical pipe of relatively small dimensions which protrudes through a roof to provide for the ventilation of gasses.

Ventilation Short Circuit
The disruption of air flow in an intake-exhaust ventilation system. For instance, if vents such as turbine vents or gable vents are placed in between the intake vents and exhaust vents (such as soffit and ridge vents) then the draw created by the Stack Effect will be disrupted and the ventilation system will be much less effective.

Ventilator
A device that circulates fresh air and expels stale air.

Verge of Popcorn Texture
A rough surface texture of Sprayed Polyurethane Foam generally considered unsuitable to receive a base coating. Nodules on this surface are larger than the valleys and an additional 50% or more of coating material is necessary to properly cover and protect the surface.

Vermiculite
One off a group of micaceous hydrated silicate minerals related to the chlorites and used in lightweight insulating concrete.

Viscocity
The resistance of a material to heat flow.

Viscous
Having a fairly high resistance to heat flow.

Void
An open space or a break in continuity; a gap.

Volatile
That which readily vaporizes; evaporates quickly.

Vulcanize
To improve the strength, resiliency, and freedom from stickiness and odor of rubber, for example, by combining with sulfur or other additives in the presence of heat and pressure.

Water Absorption
The increase in weight of a test specimen expressed as a percentage of its dry weight after being immersed in water for a specified time at a given temperature.

Water Cure
To control the rate of cure of materials such as concrete by spraying a fine mist of water on the surface.

Water Cut-off
See Night Tie-Off.

Water Guard
A turned up edge on valley metal or continuous wall flashing; used to prevent water migration under the roof system.

Water Stop
Material placed over a joint and used to prevent water entry.

Water Trough
The area in a valley where water runs. Usually referred to with open valley configurations.

Waterproof
Being resistant to moisture infiltration.

Waterproofing
The treatment of a surface or structure in order to prevent the passage of water under hydrostatic pressure.

Waterproofing Underlayment
Modified bitumen based roofing underlayments. Designed to seal to wood decks and waterproof critical leak areas. Also known as ice and water shield.

Weather
To undergo degradation in quality and appearance which is caused by exposure to the sun, wind, rain, etc.

Weep Holes
Small holes used to permit moisture to drain that has gathered inside a building component.

Weld
To join multiple metal or PVC components together by heat fusion.

Wet Bulb Temperature
Air temperature in °F as measured by a thermometer with a bulb covered by a damp wick.

Wet Film Thickness
The thickness of an uncured material such as a coating.

Wick
To convey liquid by capillary action.

Wind Clip
A clip that slips over the ends of tile, slate and other steep slope roofing materials in order to help prevent wind uplift damage.

Wind Load
The force that wind puts on structures.

Wind Uplift
(1) The upward displacement of a section of a roof system or component caused by movement of air from a location of higher air pressure, such as inside a building, to an area of lower air pressure, such as the surface of a roof during a windy day. Strong wind across the surface of a roof, especially at corners and along perimeters, creates low air pressure above the surface of the roof. Nature will automatically try to compensate for this by moving air from an area of higher pressure such as inside a building. If all penetrations and perimeters are not properly sealed, then “blow-off” can occur. (2) Displacement or blow-off of shingles or other roofing caused by the wind.

Windward
Facing into the wind.

Wire Tie
A system for attaching heavy steep slope roofing materials such as slate r tile by using wire fasteners in addition to or in place of nails.

Woven Valley
A valley construction whereby the valley has a woven look which is effected by overlapping alternate courses of shingles from both sides of the valley.

Z- or Z-Section
A piece of steel formed in the shape of a “Z.”

Zinc
A bluish-white, lustrous metallic element that is brittle at room temperature but malleable with heating. It is used to form a wide variety of alloys including brass, bronze, various solders, and nickel silver, in galvanizing iron and other metals, for electric fuses, anodes, and meter cases, and in roofing, gutters, flashings, edge metals and also for various household objects. Atomic number 30; atomic weight 65.37; melting point 419.4 °C; boiling point 907 °C; specific gravity 7.133 (25 °C); valence 2.