Pan: the bottom flat part of a roofing panel which 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: that part of a perimeter wall immediately adjacent to the roof which extends above the roof.

 

Penetration: (1) any object passing through the roof; (2) the consistency (hardness) 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 in preformed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass.

 

Permeability: (1) the capacity of a porous material to conduct or transmit fluids; (2) the amount of a fluid moving through a barrier in a unit time, unit area, and unit pressure gradient not normalized for, but directly related to, thickness.

 

Phased Application: the installation of separate roof system or waterproofing system component(s) during two or more separate time intervals. Application of surfacings at different time intervals are typically not considered phased application. (See Surfacing.)

 

Pigment: fine solid particles, which are insoluble in the vehicle, used to impart color in a coating.

 

Pinhole: a tiny hole in a coating, film, foil, membrane, or laminate.

 

Pipe Boot: prefabricated flashing piece used to flash around circular pipe penetrations.

 

Pitch: see Coal Tar, Incline, and Roof Slope.

 

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 Type I asphalt roof cement that is a trowel-able mixture of solvent-based bitumen, mineral stabilizers, other fibers and/or fillers. Generally, intended for use on relatively low slopes — not vertical surfaces. (Also see Asphalt Roof Cement and Flashing Cement.)

 

Pliability: the material property of being flexible or moldable.

 

Ply: a layer of felt, ply sheet, or reinforcement in a roof membrane or roof system.

 

Polyester: a polymeric resin which is generally cross-linked or cured and made into a variety of plastic materials and products. Polyester fibers are widely used as the reinforcing medium in reinforced membranes. (See Polyester Fiber.)

 

Polyester Fiber: a synthetic fiber usually formed by extrusion. Scrims made of polyester fiber are used for fabric reinforcement.

 

Polyvinyl Chloride (PVC): a synthetic thermoplastic polymer prepared from vinylchloride. PVC can be com-pounded 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.

 

Ponding: the excessive accumulation of water at low-lying areas on a roof.

 

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

 

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 of rainfall, during ambient drying conditions.

 

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.

 

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 which 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.

 

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”).

 

Puncture Resistance: extent to which a material is able to withstand the action of a sharp object without perforation.

 

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

 

PVC: Polyvinyl Chloride.

 

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