Term Description
Equilibrium moisture content (EMC)

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

Equiviscous temperature (EVT)

The temperature at which a bitumen attains the proper viscosity for built-up membrane application.

Equiviscous temperature (EVT) application range

The recommended bitumen application temperature range. The range is approximately 25 F below the EVT to 25 F above the EVT (50 degree Fahrenheit span). The EVT is measured in the mop cart or mechanical spreader just prior to application of the bitumen to the substrate.

Equiviscous temperature (EVT) for asphalt

The recommended EVT for roofing asphalt (ASTM D312, Type I, II, III or IV) is as follows:
mop application: the temperature at which the asphalt’s apparent viscosity is 125 centipoise.

mechanical spreader application: The temperature at which the asphalt's apparent viscosity is 75 centipoise. Note: To avoid the use of two kettles if there are simultaneous mop and mechanical spreader applications, the EVT for mechanical spreader application can be used for both application techniques.

Equiviscous temperature (EVT) for coal tar

The recommended EVT for roofing coal tar (ASTM D450, Type I or III) is the temperature at which the coal tar’s apparent viscosity is 25 centipoise.


(1) Weathering, wearing away or degradation; (2) wearing away of a coating by chalking or the abrasive action of water or windborne particles or grit.

Ethylene interpolymers (EIPs)

A group of thermoplastic compounds generally based on PVC polymers from which certain single-ply roofing membranes can be formulated.

Ethylene propylene diene terpolymer (EPDM)

A terpolymer of ethylene, propylene and diene with the residual unsaturated portion of the diene in the side chain to provide for vulcanization. It is a thermosetting synthetic elastomer. EPDM is an acronym for "ethylene propylene diene M-class rubber," which is a name assigned to this material within the classification established in ASTM D1418, "Standard Practice for Rubber and Rubber Lattices-Nomenclature."


See "equiviscous temperature."

Expanded polystyrene (EPS)

A type of plastic foam insulation product having predominately closed-cell structure manufactured from expanded polystyrene beads in a molding process; boards or blocks are formed. See "insulation."


The increase in length or volume of a material or body caused by temperature, moisture or other environmental conditions.

Expansion joint

A structural separation between two building elements that allows free movement between the elements without damage to the roof or waterproofing system.


(1) The transverse dimension of a roofing element or component not overlapped by an adjacent element or component in a roof covering. For example, the exposure of any ply in a built-up roof membrane may be computed by dividing the felt width, minus 2 inches, by the number of shingled plies; thus, the exposure of 36-inch-wide felt in a shingled, four-ply membrane should be approximately 8 1/2 inches; (2) the dimension of sidewall or roof covering that is not covered or overlapped by the upslope course of component. The typical exposure for a standard-size, three-tab shingle is 5 inches. This varies depending on manufacturer specifications.

Extensive (shallow) vegetative roof system

Vegetative roof system with a growth medium approximately 2 inches to 6 inches deep.

Exterior insulation and finish system (EIFS)

A non-load-bearing outdoor wall finish system consisting of a thermal insulation board, attachment system, reinforcement system and compatible finish.

Extruded polystyrene (XPS)

A type of plastic foam insulation product manufactured by a continuous extrusion process as the resin foams. This forms a tight and complete skin on each side of the board. See "insulation."


A process in which heated or unheated material is forced through a shaping orifice (a die) in one continuously formed shape, as in film, sheet, rod or tubing.


(1) A woven cloth or material of organic or inorganic filaments, threads or yarns used for reinforcement in certain membranes and flashings; (2) geotextile membranes used as a protective or separating layer in roof and waterproofing systems.


The outermost adhered top or bottom, or both, sheet (or layer) of an insulation board that is composed of a different material than the insulation itself. It is commonly composed of organic paper, glass mat or a combination thereof; generally impregnated or coated, or both, with asphalt, latex, or other like material; or metal foil.


Any lightening of initial color.


A reduction in bitumen softening point sometimes caused by refluxing or overheating in a relatively closed container.


(1) In steep-slope roofing, a board that is nailed to the ends of a roof rafter; sometimes supports a gutter; (2) in low-slope roofing, the vertical or steeply sloped roof or trim located at the perimeter of a building. Typically, it is a border for a low-slope roof system.


Any of a wide variety of mechanical securement devices and assemblies, including nails, staples, screws, cleats, clips and bolts, that may be used to secure various components of a roof or waterproofing assembly.


A flexible sheet manufactured by the interlocking of fibers with a binder or through a combination of mechanical work, moisture and heat. Felts are manufactured principally from wood pulp and vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers (fiberglass felts or ply sheets) or polyester fibers; other fibers may be present in each type.


Insulation composed principally of cellulose fibers usually derived from paper, paperboard stock or wood, with or without binders. See "insulation."