Term Description

Undesirable depositions of airborne spray.


(1) A weathering mechanism of materials exposed to the elements; can be promoted by elevated temperature, ultraviolet radiation, galvanic action and other agents; (2) loss of electrons by a constituent of a chemical reaction; sometimes, more specifically the combination of oxygen with a reactant.


A triatomic form of oxygen that is a bluish gas of pungent odor, chemically very active; formed naturally in the upper atmosphere by a photochemical reaction with solar ultraviolet radiation.


A platform (typically wooden) used for storing and shipping materials.


The bottom flat part of a roofing panel that is between the ribs of the panel.

Parapet wall

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


In masonry construction, a coat of cement mortar on the face of rough masonry, the earth side of foundation and basement walls, or the like.

Partially attached

A roof assembly in which the membrane has been ‚"spot affixed‚" to a substrate, usually with an adhesive or a mechanical device.

Parting agent

A material applied to one or both surfaces of a sheet to prevent sticking. Examples include fine mineral aggregate such as sand or crushed blast furnace or boiler slag and applications of silicone oils or surfactants; also called "release agent."


SI unit of measure for force per unit area (load, pressure, shear stress); 1 Pa=1 N/m2=0.2089 lb/ft2.


(1) A layer of material, usually applied by the spray method, that is allowed to reach cure before another layer ("pass") is applied; (2) a term used to explain a spray motion of the foam gun in the application of the spray polyurethane foam (SPF) material. The speed of the pass controls the thickness of the SPF.


Typically used in reference to aluminum-based coatings; for aluminum coatings, the amount of aluminum flake typically is less than the amount of paste.


A support or base for rooftop components such as pavers, pipes and small rooftop units.

Peel strength

The average load per unit width required to separate progressively a flexible member from a rigid member or another flexible member.


(1) Any construction (e.g., pipes, conduits, HVAC supports) passing through a roof or waterproofing system; (2) the consistency of a bituminous material expressed as the distance, in tenths of a millimeter (0.1 mm), that a standard needle penetrates vertically into a sample of material under specified conditions of loading, time and temperature (ASTM D5 is the test method used for bituminous materials). A cone is sometimes used for special purposes instead of a needle.

Perforated felt

Bitumen-saturated felt perforated with closely spaced small holes to allow air and moisture to escape during application of built-up roofing; depending on the type of material or specific use, can be classified in accordance with ASTM D226, D2626 or D4897 requirements.


An aggregate used in lightweight insulating concrete and preformed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass.


See "permeance."


(1) The capacity of a porous material to conduct or transmit fluids; (2) the time rate of vapor transmission through unit area of flat material of unit thickness induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions. The English (inch•pound) unit of measurement for permeability is gr/h•ft2(in•Hg/in.), which is commonly referred to as ‚"perm/inch‚" units.


(1) The rate of water vapor transmission per unit area at a steady state through a material, membrane or assembly; (2) the time rate of water vapor transmission through unit area of flat material or construction induced by unit vapor pressure difference between two specific surfaces (values in reference sources are quoted for specific material thicknesses) under specified temperature and humidity conditions. The English (inch•pound) unit of measurement for permeance is (grains)/(h•ft2•in. Hg), which is commonly referred to as ‚"perm‚" units.


A measure of the acidity or alkalinity of a solution, with neutrality represented by a value of 7; increasing acidity represented by increasingly smaller values; and increasing alkalinity represented by increasingly larger values.

Phased application

(1) The installation of a roof or waterproofing system during two or more separate time intervals or different days. Applications of surfacings at different time intervals are typically not considered phased application. See "surfacing." (2) A roof system not installed in a continuous operation.

Phenolic foam

A closed-cell, rigid, thermosetting foam insulation product with an orange or light-red foam core. Facer materials include corrugated cellulose, aluminum foil and fiberglass mat. See "insulation." Phenolic foam roof insulation can contribute to corrosion of steel roof decks because of leaching out of acidic compounds that takes place when the phenolic foam roof insulation contacts moisture.


An insoluble compounding material used to impart color.


Polyisocyanurate Insulation Manufacturers Association.