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

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

Parapet Wall: that part of a perimeter wall immediately adjacent to the roof which extends above the roof.

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.

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

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.

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.

Pipe Boot: prefabricated flashing piece used to flash around circular pipe penetrations.

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.

Plastic Cement: a roofing industry generic term used to describe Type I asphalt roof cement that is a trowel-able 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.)

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.

Polyvinyl Chloride (PVC): a synthetic thermoplastic polymer prepared from vinylchloride. PVC can be com-pounded 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.

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.

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.

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.

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").

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.

Photo Example

Rake: the sloped edge of a roof at or adjacent to the first or last rafter.

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.

Reglet: a sheet metal receiver for the attachment of counterflashing. (A reglet may be inset into a raggle, embedded behind cladding, or be surface mounted.)

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.

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.

Ridge: highest point on the roof, represented by a horizontal line where two roof areas intersect, running the length of the area.

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. Most ridge vents are either premanufactured metal or flexible, shingle-over type.

Ridging: an upward, elongated tenting displacement of a roof membrane frequently occurring over insulation or deck joints. Ridging may be an indication of movement within the roof assembly.

Roof Assembly: an assembly of interacting roof components (includes the roof deck, vapor retarder [if pre-sent], insulation, and roof covering).

Roof Curb: raised frame used to mount mechanical units (such as air conditioning or exhaust fans), skylights, etc.

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 a percent.

Roof System: a system of interacting roof components, generally consisting of membrane or primary roof covering and insulation (not including the roof deck) designed to weatherproof and, sometimes, to improve the building's thermal resistance.

Roofer: craftsman who applies roofing materials.

Rosin Paper (specifically Rosin-Sized Sheathing Paper): a nonasphaltic paper used as a sheathing paper or slip sheet in some roof systems.

Rubber: a polymeric material which, at room temperature, is capable of recovering substantially in shape and size after removal of a force. May be natural or synthetic.

Run: horizontal dimension of a slope.