Roofing Dictionary (A–Z)

Explore comprehensive roofing terms and definitions in our A-Z guide. Learn about materials, techniques, and components for better roofing knowledge.

AlligatoringA pattern of cracking in the surface of asphalt or bitumen on a built-up roof (BUR), resembling an alligator’s hide. This is caused by aging and the limited ability of asphalt to expand and contrast with temperature changes.

AsphaltA dark brown to black cementitious material in which the predominant constituents are bitumen’s. Occurs naturally or is refined from petroleum and commonly used in roofing systems.

BitumenA generic term for amorphous, semi-solid mixtures of complex hydrocarbons derived from organic sources. In roofing, this includes asphalt and coal tar.

BlisterA raised, spongy area of a roof membrane caused by trapped air or moisture vapor beneath the surface. Blisters typically indicate ply separation within the roofing system.

Built-Up Roof Membrane (BUR)A continuous, semi-flexible roofing system consisting of multiple plies of saturated felts, fabrics, or mats, bonded together with alternating layers of bitumen and typically surfaced with gravel or mineral aggregate.

Can’t StripA beveled strip (typically wood or fiberboard) installed at roof-to-wall intersections to ease the transition between horizontal and vertical surfaces and reduce membrane stress.

CaulkingA pliable sealant applied at ambient temperatures to fill joints or cracks and remain flexible after curing.

Coal Tar PitchA dark brown to black semi-solid hydrocarbon residue produced during coal tar distillation. Used as a waterproofing agent in low-slope or dead-level roofing systems. (ASTM D450)

CopingA protective cap installed on top of a parapet or wall, typically sloped to shed water and protect the wall from weather exposure.

CounterflashingFormed metal or elastomeric material installed over base flashing to protect its upper edge and fasteners from water intrusion.

CurbA raised frame or box built above the roof deck to support rooftop penetrations such as skylights, HVAC units, or roof hatches.

Dead-Level AsphaltA roofing asphalt with a softening point of approximately 140°F (60°C), meeting ASTM D312 Type I requirements.

Dead-Level RoofA roof with zero slope—completely horizontal. Dead-level roofs require special drainage and waterproofing considerations.

DeckThe structural surface (steel, wood, or concrete) to which the roofing system and insulation are applied.

DelaminationSeparation of layers within a roofing membrane or laminated insulation, often caused by moisture intrusion or poor adhesion.

Downspout (Leader)A vertical pipe that carries water from gutters to the ground or storm drainage system.

EPDMEthylene Propylene Diene Monomer. A synthetic rubber single-ply roofing membrane known for flexibility and long service life.

Expansion JointA designed separation in a building structure that allows movement due to thermal expansion, contraction, or seismic activity, preventing membrane splitting.

Factory Mutual (FM)An insurance-related testing organization that evaluates roofing assemblies for fire resistance and wind uplift performance.

FeltA fabric manufactured from organic fibers or fiberglass and used as reinforcement in roofing membranes.

FerruleA small metal sleeve placed inside a gutter to maintain spacing and prevent deformation when gutter spikes are driven.

FishmouthA roofing defect where the edge of a membrane ply opens due to wrinkling, allowing moisture intrusion.

FlashingComponents installed to weatherproof roof edges, penetrations, walls, and transitions where the roofing system is interrupted.

GravelCoarse aggregate (typically ½"–⅝") used as surfacing on built-up roofing systems for UV protection and durability.

Gravel StopA metal edge detail that prevents loose aggregate from washing off the roof while providing a finished perimeter edge.

Heat WeldingA method of joining thermoplastic roofing membranes by melting and fusing overlapping sheets using hot air.

Infrared ThermographyA roof diagnostic technique using infrared imaging to detect temperature variations indicating trapped moisture.

JoistsStructural members (wood or steel) installed parallel to support floors or roof decks.

Modified BitumenAn asphalt-based roofing material enhanced with polymers such as SBS or APP for increased flexibility and durability.

MSDS (SDS)Material Safety Data Sheet (now Safety Data Sheet). Provides information on handling, hazards, and safety procedures for materials.

Parapet WallA perimeter wall that extends above the roof surface.

Pipe BootA flexible or pre-formed flashing component used to seal around pipe penetrations.

PVCPolyvinyl Chloride. A thermoplastic single-ply roofing membrane with heat-welded seams and chemical resistance.

RegletA groove cut into a wall or curb to receive and secure counterflashing.

RidgingAn upward tenting or buckling of the roofing membrane, often occurring over joints or seams due to improper installation.

Sprayed Polyurethane Foam (SPF)A roofing system formed by spraying two liquid components that expand into a rigid, fully adhered, insulating, and water-resistant membrane.

Standing SeamA metal roofing system characterized by raised, interlocking vertical seams that conceal fasteners.

Thermoplastic Olefin (TPO)A single-ply roofing membrane made from polypropylene and ethylene-propylene polymers with added UV stabilizers and flame retardants.

ThermoplasticMaterials that soften when heated and harden when cooled, allowing seams to be heat-welded.

ThermosetMaterials that cure irreversibly when heated or chemically activated (e.g., EPDM).

UL (Underwriters Laboratories)An independent safety science organization that tests and certifies roofing assemblies for fire resistance and performance.

Vapor BarrierA material installed within a roof assembly to limit the migration of water vapor from the building interior into the insulation and roofing system.

Walkway PadsDurable pads or pavers installed on roof surfaces to protect the membrane from foot traffic and maintenance activity.

Wind UpliftThe upward force exerted on a roofing system by wind pressure, which roofing assemblies must be designed to resist.

XPS (Extruded Polystyrene)A rigid foam insulation commonly used in roofing assemblies, known for high compressive strength and moisture resistance.

YieldThe coverage rate of a roofing material, typically expressed as square feet per gallon or per unit.

Zinc Coating (Galvanization)A protective zinc layer applied to steel roofing components to prevent corrosion.