This glossary contains many useful terms and definitions that will help you understand much of the work we do at ROOFCORP.

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Pallet: a platform (typically wooden) used for storing and shipping materials.

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

Pan former: power roll-forming equipment that produces a metal roofing panel from a flat sheet.

Parapet wall: the part of a perimeter wall that extends above the roof.

Parge: 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 roofing 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 blocking.

Pascal: SI unit of measure for force per unit area; 1 Pa=1 N/m2.

Pass: (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.

Pass line: the junction of two passes of SPF. A distinct line is formed by the top skin of the bottom pass and the next pass adhering to this skin.

Pedestal: a support or base for roof top components such as pavers, pipes and small roof top units.

Peel strength: the average load per unit width required to separate progressively a flexible member from a rigid member or another flexible member.

Penetration: (1) any construction (e.g., pipes, conduits, HVAC supports) passing through the roof; (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.

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

Perm: see Permeance.

Permeability: (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/hr·ft2·(in. Hg/in.), which is commonly referred to as “perm·inch” units.

Permeance: (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, under specified temperature and humidity conditions. The English (inch·pound) unit of measurement for permeance is gr/h·ft2·in. Hg, which is commonly referred to as “perm” units.

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

Phased application: the installation of a roofing or waterproofing system during two or more separate time intervals or different days. Application of surfacings at different time intervals are typically not considered phased application. (see Surfacing.) A roofing system not installed in a continuous operation.

Picture framing: a square or rectangular pattern of ridges in a roof membrane or covering over insulation or deck joints.

Pigment: an insoluble compounding material used to impart color. Pinhole: a tiny hole in a coating, film, foil, membrane or laminate comparable in size to one made by a pin.

Pipe boot: prefabricated flashing piece used to flash around circular pipe penetrations. Pitch: see Coal tar.

Pitch-pocket (Pitch-pan): a flanged, open bottomed enclosure made of sheet metal or other material, placed around a penetration through the roof, filled with grout and bituminous or polymeric sealants to seal the area around the penetration.

Pittsburgh lock seam: a method of interlocking metal, usually at a slope change.

Plastic cement: a roofing industry generic term used to describe asphalt roof cement that is a trowelable mixture of solvent-based bitumen, mineral stabilizers, and other fibers and/or fillers. Generally, intended for use on relatively low slopes, not vertical surfaces. (also see Asphalt roof cement and Flashing cement.)

Plasticizer: a material incorporated in a material to increase its ease of workability, flexibility or distensibility.

Plasticizer migration: in some thermoplastic roofing membranes, the loss of plasticizer chemicals from the membrane, resulting in shrinkage and embrittlement of the membrane, typically PVC.

Pliability: the material property of being flexible or moldable.

Ply: a layer of felt or ply sheet in a built-up roof membrane or roof system.

PMR: protected membrane roof. Polychloroprene: see Neoprene.

Polyester: a polymer in which the repeated structural unit in the chain is of the ester type.

Polyisobutylene (PIB): a product formed by the polymerization of isobutylene. May be compounded for use as a roof membrane material.

Polymer: a macromolecular material formed by the chemical combination of monomers having either the same or different chemical composition.

Polymer modified bitumen: see Modified bitumen.

Polymeric methylene diphenyl diisocyanate (PMDI): component A in SPF. An organic chemical compound having two reactive isocyanate groups. It is mixed with the B component to form polyurethane.

Polymerization: a chemical reaction in which monomers are linked together to form polymers.

Polypropylene: a polymer prepared by the polymerization of propylene as the sole monomers.

Polyol: a polyhydric alcohol, i.e., one containing three or more hydroxyl groups, one component of polyisocyanu-rate and polyurethane compounds.

Polyvinyl chloride (PVC): a synthetic thermoplastic polymer prepared from vinylchloride. PVC 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.

Polystyrene: a polymer prepared by the polymerization of styrene as the sole monomer.

Pond: a surface which is incompletely drained.

Ponding: the excessive accumulation of water at low-lying areas on a roof that remains after the 48 hours after the end rainfall under conditions conducive to drying.

Pop rivet: a relatively small-headed pin with an expandable head for joining light gauge sheet metal.

Popcorn surface texture: in SPF roofing, the condition in which the foam surface shows a coarse texture where valleys form sharp angles. This surface is unacceptable for proper coating and protection.

Positive drainage: the drainage condition in which consideration has been made during design for all loading deflections of the deck and additional roof slope has been provided to ensure drainage of the roof area within 48 hours following rainfall during conditions conducive to drying.

Positive side waterproofing: an application where the waterproofing systems and the source of the hydrostatic pressure are on the same side of the structural element.

Pot life (Working life): the period of time during which a reacting composition remains suitable for its intended processing after mixing with reaction initiating agents .

Pourable sealer: a type of sealant often supplied in two parts and used at difficult-to-flash penetrations, typically in conjunction with pitch-pockets to form a seal.

Press brake: a machine used in cold-forming sheet metal or strips of metal into desired profiles.

Prestressed concrete: concrete in which the reinforcing cables, wires or rods in the concrete are tensioned before there is load on the structural member, holding the concrete in compression for greater strength.

Pre-tinning: coating a metal with solder or tin alloy prior to soldering or brazing it.

Primer: (1) a thin, liquid-applied solvent-based bitumen that may be applied to a surface to improve the adhesion of subsequent applications of bitumen; (2) a material that is sometimes used in the process of seaming single-ply membranes to prepare the surfaces and increase the strength (in shear and peel) of the field splice; (3) a thin liquid-applied material that may be applied to the surface of SPVF to improve the adhesion of subsequent application of SPVF protective coatings.

Proportioner: the basic pumping unit for SPF or two-component coating systems. Consists of two positive displacement pumps designed to dispense two components at a precisely controlled ratio.

Protection course: a sacrificial material used to shield a waterproofing material from damaging external forces.

Protection mat: a sacrificial material used to shield one roof system component from another.

Protected membrane roof (PMR): an insulated and ballasted roofing assembly in which the insulation and ballast are applied on top of the membrane (sometimes referred to as an “inverted roof assembly”).

Psychrometer: an instrument used to measure humidity in the atmosphere from two thermometers which are similar except that the bulb of one is kept wet, the bulb of the other being dry.

Psychrometric chart: chart showing the relationship between dew point temperature, dry bulb temperature, wet bulb temperature and relative humidity.

Puncture resistance: the ability of a material to withstand the action of a penetrating or puncturing object.

Purlin: horizontal secondary structural member that transfers loads from the primary structural framing.

PVC: polyvinyl chloride.