Roofing Terminology

A-component (A-side)
One component of a two-component polymer system; for polyurethane foam and coatings, the isocyanate component.

Apron Flashing
A term used for a flashing located at the juncture of the top of a sloped roof and a vertical wall, chimney or steeper-sloped roof.

Bitumen
(1) A class of amorphous, black or dark-colored, (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of high-molecular-weight hydrocarbons, soluble in carbon disulfide, and found in asphalts, tars, pitches and asphaltites; (2) a generic term used to denote any material composed principally of bitumen, typically asphalt or coal tar.

Cool Roof
A roof system that uses products made of highly reflective and emissive materials for its top surface. Cool roof surfaces can remain at markedly lower temperatures when exposed to solar heat in service than surfaces of roofs constructed with traditional non-reflective roofing products.

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

Elastomeric coating
A coating that is capable of being stretched at least twice its original length (100 percent elongation) and recovering to its original dimensions.

Emissivity
(1) Infrared emissivity is a measure of the ability of a surface to shed some of its absorbed heat (in the form of infrared radiation) away from the surface; emissivity is expressed as a percentage or a decimal factor; (2) the ratio of radiant energy emitted from a surface under measurement to that emitted from a black body (the perfect emitter and absorber) at the same temperature.

Foam stop
The roof edge treatment upon which spray polyurethane foam (SPF) is terminated.

Parapet wall
The part of a perimeter wall that extends above a roof.

Single-ply roofing
A roof system in which the principal roof covering is a single-layer flexible thermoset or thermoplastic membrane.

Spray polyurethane foam (SPF)
A foamed plastic material, formed by mixing and spraying two components, methylene diphenyl diisocynate (MDI) ("A-component") and resin containing a polyol ("B-component") to form a rigid, fully adhered, water-resistant and insulating membrane.

Thermal resistance (or R-Value)
The quantity determined by the temperature difference at steady state between two defined surfaces of a material or construction that induces a unit heat flow rate through a unit area. In English (inch•pound) units, it is expressed as F•ft²•h/Btu.

Note 1: A thermal resistance (R) value applies to a specific thickness of a material or construction.

Note 2: The thermal resistance (R) of a material is the reciprocal of the thermal conductance (C) of the same material (i.e., R = 1/C).

Note 3: Thermal resistance (R) values can be added, subtracted, multiplied and divided by mathematically appropriate methods.

Source: National Roofing Contractor Association