Roofing Terms P – R
- -P-
- 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. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 995
- 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. (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 polyisocyanurate 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. The NRCA Roofing and Waterproofing Manual—Fifth Edition 996 Glossary
- 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 liquidapplied 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.
- Top of Page
- -R-
- R-value
- see Thermal Resistance.
- Racking
- a method of asphalt shingle application, also referred to as the straight-up method, whereby shingle courses are applied vertically, up the roof rather than laterally or across and up. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 997
- Rafter
- one of a series of sloped structural members, that extend from the ridge or hip to the downslope perimeter or eave, designed to support the roof deck and its associated loads.
- Raggle
- a groove or slot, often cut in a masonry wall or other vertical surface adjoining a roof, for inserting an inset flashing component such as a reglet.
- Rake
- the sloped edge of a roof at or adjacent to the first or last rafter.
- Rake-starter (Bleeder strip)
- starter-strip used along rake edges in conjunction with asphalt shingle roofing.
- Re-cover
- the addition of a new roof membrane or steep-slope roof covering over a major portion of an existing roof assembly. This process does not involve removal of the existing roofing.
- Reflectivity
- see Light Reflectance.
- Reglet
- a sheet metal receiver for the attachment of counterflashing. A reglet may be surface-mounted, inset into a raggle or embedded behind cladding.
- Reinforced membrane
- a roofing or waterproofing membrane that has been strengthened by the addition or incorporation of one or more reinforcing materials, including woven or nonwoven glass fibers, polyester mats or scrims, nylon, or polyethylene sheeting.
- Relative humidity (RH)
- the ratio of the pressure of water vapor present in a given volume of air to the pressure of fully saturated water vapor at the same temperature, expressed as a percentage.
- Release tape (or Strip)
- a plastic film or paper strip that is applied to the back of self-sealing shingles and other materials. The strip prevents the material from sticking together in the roll or bundle. With asphalt shingles, the strip need not be removed for application of the shingles.
- Replacement
- the practice of removing an existing roof system down to the roof deck and replacing it with a new roofing system.
- Reroofing
- the process of re-covering, or tearing-off and replacing an existing roof system.
- Resin
- component B in SPF. This component contains a catalyst, blowing agent, fire retardants, surfactants and polyol. It is mixed with the A component to form polyurethane.
- Ridge
- highest point on the roof, represented by a horizontal line where two roof areas intersect, running the length of the area.
- Ridge cap
- a material or covering applied over the ridge of a roof.
- Ridge course
- the last or top course of roofing materials, such as tile, roll roofing, shingles, etc., that covers the ridge and overlaps the intersecting field roofing.
- Ridge vent
- a ventilator located at the ridge that allows the escape of warm and/or moist air from the attic area or rafter cavity.
- Ridging
- see Buckle.
- Roll materials
- a general term applied to rolls of roofing felt, ply sheet, etc., which are typically furnished in rolls.
- Roll roofing
- coated felts, either smooth or mineral-surfaced.
- Roof
- (1) the cover of a building; (2) to cover with a roof.
- Roof area divider
- refer to area divider.
- Roof area expansion Joint
- see Expansion Joint. The NRCA Roofing and Waterproofing Manual—Fifth Edition 998 Glossary
- Roof assembly
- an assembly of interacting roof components including the roof deck, vapor retarder (if present), insulation and roof covering.
- Roof cement
- see Asphalt Roof Cement or Coal Tar Roof Cement.
- Roof covering
- the exterior roof cover or skin of the roof assembly, consisting of membrane, panels, sheets, shingles, tiles, etc.
- Roof curb
- raised frame used to mount mechanical units (such as air conditioning or exhaust fans), skylights, etc. on a roof.
- Roof jack
- a metal or wood bracket used to support toe-boards on steep-slope roofs. (see Flashing Collar.)
- Roof overhang
- a roof extension beyond the exterior wall of a building.
- Roof seamer
- (1) machine that crimps neighboring metal roof panels together; (2) machine that welds laps of membrane sheets together using heat, solvent, or dielectric energy.
- Roof slope
- the angle a roof surface makes with the horizontal, expressed as a ratio of the units of vertical rise to the units of horizontal length (sometimes referred to as run). For English units of measurement, when dimensions are given in inches, slope may be expressed as a ratio of rise to run, such as 4:12 or as an angle.
- Roof system
- a system of interacting roof components, generally consisting of a membrane or primary roof covering and roof insulation (not including the roof deck) designed to weatherproof and, sometimes, to improve the building’s thermal resistance.
- Rosin paper (specifically Rosin-sized sheathing paper)
- a nonasphaltic paper used as a sheathing paper or slip sheet in some roof systems.
- Rubber
- a material that is capable of recovering from large deformations quickly and forcibly.
- Run
- horizontal dimension of a slope.
- Top of Page