Roofing Glossary of Terms





Roof Vent Pipe Field of Roof System Ridge Flashing Hip Soffit Gable Rake Drip Edge Valley Gutters Underlayment Eave Vent
PalletA platform used to hold materials.
Pan(1) The concave piece of "Pan and Cover" tile whose rounded surface touches the top side of the roof substrate. <BR><BR>(2) The flat part of a roofing panel located between the ribs.
Pan FlashingA sheet metal flashing that covers an equipment platform and is designed to counter flash the base flashings surrounding the platform.
Parapet WallThat part of a perimeter wall that extends above the surface of the roof.
PassThe term used to describe the application of one layer of Spray Polyurethane Foam (SPF). The speed of a pass will determine foam thickness.
Pass LineThe distinct line formed between two passes of SPF. This line is the top skin of the bottom pass of the SPF.
PenetrationAny object that pierces the surface of the roof.
Percent ElongationThe maximum amount that a material can be lengthened or stretched before breaking; expressed as a percentage of the original length of material tested.
PerliteA natural volcanic glass having distinctive concentric cracks and a relatively high water content.. Perlite in a fluffy heat expanded form is used in lightweight insulating concrete, fire-resistant rigid insulation board (R = 2.78 per inch) and potting soil.
PermA unit of water vapor transmission, defined as one grain of water vapor per square foot per hour per inch of mercury (Hg) pressure difference (1 inch of mercury = 0.491 psi).
PermeabilityThe rate of flow of a liquid or gas through a porous material.
pHA measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.
PhasingInstalling roof system components in separate time intervals. For instance, installing a base sheet, and then two plies of roofing one day, and coming back and installing the remaining two plies one or more days later. It is generally not considered Phasing if the surfacing is applied at a later date.
Picture FramingRectangular patterns seen in a roof that are created by buckles or ridges in the roof system or sumps in the substrate.
PIMAPolyisocyanurate Insulation Manufacturers Association
PinholeA small hole in a coating, foil, membrane, or other roofing material.
Pipe BootA prefabricated flashing piece used to flash around circular pipe penetrations. Also known as a Roof Jack. Click here for an example.
PitchTerm used to describe Roof Slope and also short for Coal Tar Pitch.
Pitch Pocket (a.k.a. Pitch Pan)A flanged piece of flashing material placed around irregularly shaped roof penetrations and filled with grout and a pourable sealer to seal around the penetration in order to seal it from against moisture entry. Pitch pockets are a good source of leaks and should be avoided if possible.
Pittsburgh Lock SeamA method of interlocking two separate pieces of metal.
Plastic CementA term used to describe Type I asphalt roof cement. Plastic cement should not be used on vertical surfaces. See also Asphalt Roof Cement and Flashing Cement.
Plastic FilmA flexible sheet made by the extrusion of thermoplastic resins.
PlasticizersMaterial incorporated into rubber and plastic in order to increase their flexibility and workability.
PlenumA space or enclosure in which air or other gas is at a pressure greater than that of the outside atmosphere.
PlyA layer of felt or other reinforcement material in a roof system.
PMRSee Protected Membrane Roof.
PolyesterAny of numerous synthetic polymers produced chiefly by reaction of dibasic acids with Dihydric alcohols and used primarily as light, strong, weather-resistant resins. In roofing, polyester is used to reinforce fabrics.
PolymerAny of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule.
Polymer Modified BitumenSee Modified Bitumen.
Polymeric Methylene Diphenyl Diisocyanate (PMDI)The "A" component in SPF; when mixed with "B", it forms polyurethane. PMDI is an organic chemical compound having two reactive Isocyanate (-N=C=O) groups.
PolymerizationThe combining of monomers to produce polymers.
PolypropyleneAny of various thermoplastic resins that are polymers of propylene. They are hard and tough, and are used to make molded articles and fibers.
Polyvinyl Chloride (PVC)A thermoplastic polymer that 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.
PondingThe accumulation of water at low-lying areas on a roof.
Pop RivetA small metal pin having a head on one end, inserted through aligned holes in pieces of light gauge metal to be joined and then the head is expanded to join the metal.
Popcorn Surface TextureA coarse surface texture of SPF considered unacceptable for coatings.
Positive DrainageThe drainage condition of a roof where all water is gone from the roof surface within forty-eight hours of precipitation during normal drying conditions.
Pot LifeThe period of time during which a material with multiple ingredients can be applied or administered after being mixed together.
Pourable SealerA type of sealant that is initially in liquid form commonly used in conjunction with pitch pans to form a water-tight barrier around penetrations that are difficult to flash.
Press BrakeA mechanical device used to form sheet metal into desired shapes and profiles.
PrimerA material that is applied to a surface in order to increase that surface’s ability to adhere to or work in conjunction with a subsequently applied material.
ProportionerA pumping unit comprised of two (2) positive displacement pumps that is designed to dispense two (2) components at a precise ratio. Used in SPF and plural component coating applications.
Protected Membrane Roof (PMR)A roof assembly in which the insulation and ballast are placed on top of the membrane component. Commonly referred to as an "inverted roof assembly."
PsychrometerAn instrument that uses the difference in readings between two thermometers, one having a wet bulb and the other having a dry bulb, to measure the moisture content or relative humidity of air.
Puncture ResistanceThe ability of a material to withstand being pierced by a sharp object.
PurlinHorizontal secondary structural member used to transfer loads from the primary structural members.
PVCSee Polyvinyl Chloride.




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Rough Estimator

Roofing contractors have a language all their own. Don’t get bogged down by the jargon. Check out the glossary for clear, simple definitions of roofing terminology.