Term Description
Polyurethane foam (cellular polyurethane)

Insulation composed principally of the catalyzed reaction product of polyisocyanate and polyhydroxy compounds, processed usually with fluorocarbon gas to form a rigid foam having a predominately closed-cell structure. It is sprayed-in-place or preformed into boards. See "insulation."
Polyvinyl chloride (PVC)

A synthetic thermoplastic polymer prepared from vinyl chloride. 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.
Polyvinylidene fluoride (PVDF)

A highly nonreactive thermoplastic fluoropolymer. PVDF, known by the registered trade names of Kynar 500® and Hylar 5000,® is used as the principal ingredient in high-quality paints and protective coatings for metals, including architectural sheet metal and metal roofing applications. PVDF coatings have good gloss and color retention and are reported to resist chalking, cracking and fading.
Ponding

The excessive accumulation of water at low-lying areas on a roof that remains more than 48 hours after precipitation under conditions conducive to drying.
Popcorn surface texture

In spray polyurethane foam 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.
Portland cement

A hydraulic (sets and hardens by chemical reaction with water and is capable of doing so under water) cement used for making concrete and grout. Portland cement is a mixture that consists of calcium carbonate and clay-like minerals or other silica-, alumina- and iron-oxide bearing materials; various types are formulated and manufactured.
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 rain during conditions conducive to drying.
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.
Pour coat

See "flood (pour) coat."
Pourable sealer

A type of sealant often supplied in two parts and used at difficult-to-flash penetrations, typically in conjunction with penetration pockets to form a seal.
Pre-tinning

Coating a metal with solder or tin alloy prior to soldering or brazing it.
Pressure-sensitive

A term used to describe a category of adhesives that in dry (solvent-free) form are tacky at room temperature and adhere to a variety of dissimilar surfaces when contact is promoted by application of pressure. Pressure-sensitive adhesives do not require activation by an energy source such as heat.
Prestressed concrete

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

Primary drainage

Drainage devices, such as drains or scuppers, that provide for the direct removal of water from a waterproofing system.
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 spray polyurethane foam (SPF) to improve the adhesion of subsequent application of SPF protective coatings.
Protected membrane roof (PMR)

An insulated and ballasted roof assembly in which the insulation and ballast are applied on top of the membrane (sometimes referred to as an inverted roof assembly).
Protection course

(1) A sacrificial material used to shield a waterproofing material from damaging external forces; (2) a separate layer of material installed on top of the membrane to protect a vegetative roof waterproofing membrane from damage.
Protection mat

A sacrificial material used to shield one roof system component from another.
PSI

Pounds per square inch.
Psychrometric chart

A 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

A horizontal secondary structural member that transfers loads to the primary structural framing.
PVC

See "polyvinyl chloride (PVC)."
PVDF

See "polyvinylidene fluoride (PVDF)."
R-value

See "thermal resistance (R)."

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