Glossary of Roofing and Waterproofing Terms

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Off-Ratio Foam: SPF which has excess isocyanate or resin. Off-ratio will not exhibit the full physical properties of normal SPF.

Open Time: the period of time after an adhesive has been applied and allowed to dry, during which an effective bond can be achieved by joining the two surfaces.

Open Valley: a method of valley construction in which the steep-slope roofing on both sides are trimmed along each side of the valley, exposing the valley flashing.

Orange Peel Surface Texture: the surface shows a fine texture and is compared to the exterior skin of an orange. This surface is considered acceptable for receiving a protective coating. The theoretical coverage rate cannot be used without adding a minimum 10% additional material to adequately cover the orange peel texture.

Organic: being or composed of hydrocarbons or their derivatives originating from plant or animal matter.

Organic Felt: an asphalt roofing base material manufactured from cellulose fibers.

Organic Shingle: an asphalt shingle reinforced with material manufactured from cellulose fibers.

ORNL: Oak Ridge National Laboratory

Osmosis: the diffusion of fluids through a semi-permeable membrane or porous partition.

Overspray: undesirable depositions of airborne spray loss.

Overspray Surface Texture: the surface shows a linear coarse textured pattern and/or a pebbled surface. This surface is generally downwind of the sprayed polyurethane path and is unacceptable for proper coating coverage and protection, if severe. The minimum percentage of additional material to be added will vary from 25% to 50% depending upon the type of surface texture.

Ozone Resistance: the ability of a material to resist the deteriorating effects of ozone exposure.

Pallet: a platform (typically wooden) used for storing and shipping materials.

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.

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.

Pascal (N/m2): Sl unit of measure for force per unit area.

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.

Peel Strength: the average force (or force per unit width) required to peel a membrane or other material from the substrate to which it has been bonded.

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.

Percent Elongation: in tensile testing, the increase in the gauge length of a specimen measured at or after fracture of the specimen within the gauge length. Usually expressed as a percentage of the original gauge length.

Perlite: an aggregate used in lightweight insulating concrete and in preformed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass.

Perm: a unit of water vapor transmission defined as 1 grain of water vapor per square foot per hour per inch of mercury pressure difference (1 inch of mercury = 0.49 psi). The formula for perm is: P = Grains of Water Vapor/Square Foot.Hour~lnch Mercury (P = grain~in/ft2.h~in Hg [P = ng/(Pa~s~m)]).

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.

Permeance: the rate of water vapor transmission per unit area at a steady state through a material, membrane or assembly, expressed in Grain/Square Foot.Hour~lnch Mercury (grain/ft2.h~in Hg [ng/Pa~a~m2]).

pH: a measure of acidity/alkalinity of aqueous mixtures. A measure of pH 7 is neutral, lower is more acidic.

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.)

Picture Framing: a square or rectangular pattern of buckles or ridges in a roof covering generally coinciding with insulation or deck joints; generally, a function of movement of the substrate.

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

PIMA: Polyisocyanurate Insulation Manufacturers Association

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 trowelable 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.)

Plastic Film: a flexible sheet made by the extrusion of thermoplastic resins.

Plasticizer: a material, frequently solvent-like, incorporated in a plastic or a rubber to increase its ease of workability, flexibility, or extensibility.

Plastomeric: a plastic-like polymer consisting of any of various complex organic compounds produced by polymerization, and capable of being molded, extruded, or cast into various shapes or films.

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.

PMR: Protected Membrane Roof.

Polychloroprene: see Neoprene.

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.

Polyisobutylene (PIB): a product formed by the polymerization of isobutylene. May be compounded for use as a roof membrane material.

Polymer: a natural or synthetic chemical compound of high molecular weight, or a mixture of such compounds, formed when monomers (small individual molecules) are combined to form large long-chain molecules.

Polymer Modified Bitumen: See Modified Bitumen.

Polymeric Methylene Diphenyl Diisocyanate (PMDI): component A in SPF. An organic chemical compound having two reactive isocyanate (-N=C=O) groups. It is mixed with the B component to form polyurethane.

Polymerization: the process whereby monomers are combined to form large, chainlike molecules.

Polypropylene: a tough, lightweight plastic made by the polymerization of high-purity propylene gas.

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.

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.

Popcorn Surface Texture: the 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 of rainfall, during ambient drying conditions.

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: the period of time during which a multi-component or catalytically cured material remains suitable for application after being mixed.

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.

Pre-Tinning: coating a metal with solder or tin alloy, prior to soldering or brazing it.

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 member, holding the concrete in compression for greater strength.

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.

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.

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: a device for measuring ambient humidity by employing a dry bulb thermometer and a wet bulb thermometer.

Psychrometric Chart: a diagram relating the properties of humid air with temperature.

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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