Panel clip—Independent clip used to attach roof panels to substructure.

Panel creep—The tendency of the transverse dimension of a roof panel to gain in modularity due to spring-out or storage-distortion.

Parapet—That portion of the vertical wall of a building which extends above the roof line at the intersection of the wall and roof.

Parapet wall—That part of any wall entirely above the roof.

Pascal—SI unit of measure for force per unit area (N/m2).

Peak—The uppermost point of a gable.

Peak sign—A sign attached to the peak of the building at the end wall showing the building manufacturer.

Penetration—The consistency of a bituminous material expressed as the distance in tenths of a millimetre (0.1 mm) that a standard needle or cone vertically penetrates a sample of material under specified conditions of loading, time, and temperature.

Percent elongation—In tensile testing, the increase in the gauge length, measured after fracture of the specimen within the gauge length. Usually expressed as a percentage of the original gauge length.

Percent water by volume—
Volume of Water in Sample x lOO
Volume of Sample Percent water by weight — x lOO
Sample weight wet—Sample weight dry Sample weight dry.

Perlite—An aggregate used in lightweight insulating concrete and in preformed perlite insulating board; formed by .heating and expanding siliceous volcanic glass.

Perm—(vapor transmission)—A unit to measure water vapor transmission—one grain of water vapor per square foot per hour perinch of mercury pressure difference. 1 Perm= 1 grain/h'ftMn. Hg.

Permeability—(1) The capacity of a porous medium to conduct or transmit fluids; (2) The amount of liquid moving through a barrier in a unit time, unit area and unit pressure gradient not normalized for but directly related to thickness; (3) The product of vapor permeance and thickness (for thin films, ASTM E96-over 1/8", ASTM C355). Usually reported in perm inches or grain/h'ftMn. Hg per inch of thickness.

Permeance—The rate of water vapor transmission per unit area at a steady state through a membrane or assembly, expressed in ng/Pa»s»m2 (grain/ft^h'in. Hg).

Petroleum pitch—A dark brown to black, predominantly aromatic, solid cementitious material obtained by the processing of petroleum, petroleum fractions, or petroleum residuals.
pH—(1) The negative log of the hydrogen ion concentration, a measure of acidity and alkalinity. (2) A measure of the relative acidity of alkalinity for water. A pH of 7.0 indicates a neutral condition. A greater pH indicates alkalinity and a lower pH, acidity. A one unit change in pH indicates a tenfold change in acidity and alkalinity.

Phased application—The installation of a roofing or waterproofing system during two or more separate time intervals; a roofing system not installed in a continuous operation.

Phenolic plastics—Plastics based on resins made by the condensation of phenols, such as phenol and cresol, with aldehydes.

Picture framing—A rectangular pattern of ridges in a membrane over insulation or deck joints.

Picture temperature level control—A control on an infrared imaging system which is used to move the thermal range being viewed to include areas of interest.

Pig spout—A sheet metal flashing designed to direct the flow of water out through the face of the gutter rather than through a downspout.

Pilaster—A reinforced or enlarged portion of a masonry wall to provide support for roof loads or lateral loads on the wall.

Pinhole—A tiny hole in a film, foil, or laminate comparable in size to one made by a pin.

Pitch—See Incline; Coal tar pitch; or Petroleum pitch.

Pitch pocket—A flanged, open bottomed metal container placed around a column or other roof penetration, and filled with hot bitumen or flashing cement to seal the joint.

Plastic—A material that contains as an essential ingredient one or more organic polymeric substances of large molecular weight, is solid in its finished state and at some stage in its manufacture or processing into finished articles, can be shaped by flow.

Plastic cement—See Flashing cement

Plastic design—A design concept based on multiplying the actual loads by a suitable load factor and using the yield stress as the maximum stress in any member.

Plastic roof or wall panels—Panels used to admit light. They are normally of the same configuration as the metal roof or wall panels, and installed in the same plane.

Plasticizer—Material, frequently solvent-like, incorporated in a plastic or a rubber to increase its ease of workability, flexibility, or extensibility. Adding the plasticizer may lower the melt viscosity, the temperature of the second order transition, or the elastic modulus of the polymer.

Plasticizers—May be monomeric liquids (phthalate esters), low molecular weight liquid polymers (polyesters) or rubbery high polymers (E/VA). The most important use of plasticizers is with PVC where the choice of plasticizer will dictate under what conditions the membrane may be used.

Plastisols—Mixtures of resins and plasticizers which can be cast or converted to continuous films by the application of heat.

Ply—A layer of felt in a built-up roofing membrane; a four ply membrane has at least four plies of felt at any vertical cross section cut through the membrane.

Ply (Plywood)—A single veneer lamina in a glued plywood panel.

Plying cement—Any bituminous material used for adhering layers of felts, fabrics, or mats to structural surfaces and to each other.

Plywood—A flat panel built up of sheets of wood veneer called plies, united under pressure by a bonding agent to create a panel with an adhesive bond between plies as strong as or stronger than, the wood. Plywood is constructed of an odd number of layers with grain of adjacent layers perpendicular. Layers may consist of a single ply or two or more plies laminated with parallel grain direction. Outer layers and all odd numbered layers generally have the grain direction oriented parallel to the long dimension of the panel.

Pointing—(1) Troweling mortar into a joint after masonry units are laid. (2) Final treatment of joints in cut stonework. Mortar or a putty-like filler is forced into the joint after the stone is set.

Polyester fiber—Generic name for a manufactured fiber in which the fiber-forming substance is any long chain synthetic polymer composed of an ester of a dihydric alcohol and tereph-thalic acid. Scrims made of polyester fiber are used for fabric reinforcement.

Polyisobutylene—The polymerization product of isobutylene. It varies in consistency from a viscous liquid to a rubberlike solid with corresponding variation in molecular weight from 1,000 to 400,000.

Polymer—A macromolecular material formed by the chemical combination of monomers having either the same or different chemical composition. Plastics, rubbers, and textile fibers are all high molecular weight polymers.

Polyols—A poly hydric alcohol, i.e., one containing three or more hydroxyl groups.

Polypropylene—(C3H5)n—A synthetic thermoplastic polymer, with a molecular weight of 40,000 or more.

Poly vinyl Chloride (PVC)—A synthetic thermoplastic polymer prepared from vinylchloride. PVC can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, filler, and other modifiers; rigid forms used in pipes; flexible forms used in manufacture of sheeting.

Pond—A roof area that retains water instead of draining after rainfall.

Ponding—Water in low or irregular roof areas that remains longer than 48 hours after the cessation of rainfall.

Pop rivet—See Blind rivet

Pot life—The working time once a product has been reacted (catalyzed).

Pre-painted coil—Coil steel which receives a paint coating prior to the forming operation.

Present value—In Life Cycle Cost analysis, the procedure of relating expenses at some future time to present time to permit comparison of alternatives in equivalent terms.

Press brake—A machine used in cold-forming metal sheet or strip into desired cross section.

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

Preventative maintenance—The regular, scheduled, inspection for and the repair of normal, expected failures of plant facilities.
Primary framing—The main load carrying members of a structural system, generally the columns and rafters or other main support members.

Primary members—The main load carrying members of a structural system, including beams, columns, endwall posts, rafters, or other main support members.

Prime coat—First coat applied in coil coating process to about 0.2 mils thick and cured under heat.

Primer (bituminous)—A thin liquid bitumen applied to a surface to improve the adhesion of heavier applications of bitumen and to absorb dust.

Primer paint—This is the initial coat of paint applied in the shop to the structural framing of a building for protection against the elements during shipping and erection.

Proportional limit—The greatest stress which a material is capable of sustaining without any deviation from proportionality of stress to strain (Hooke's Law). It is expressed in force per unit area. (ASTMD-1621)

Protected membrane roof (PMR)—Roof assembly with insulation on top of membrane instead of vice versa, as in conventional roof assembly (also known as inverted or upside-down roof assembly).

Puncture resistance—Extent to which a material is able to withstand the action of a sharp object without perforation.

Purlin—A horizontal secondary structural member bolted to the rafters which transfers the roof loads from the roof covering to the rafters or primary frames.