Roofing Terminology
(Click on a letter to learn more)
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Parapet Wall
Perimeter wall, which extends above the roof.
Peel Strength
Average force required to peel a membrane from the substrate to which it has been bonded.
Penetration
Any object passing through the roof.
Perlite
An aggregate used in lightweight insulation concrete and in preformed perlitic insulation board, formed by heating and expanding siliceous volcanic.
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 = 0.491 psi).
Phase Application
The installation of a roof system or waterproofing system during two or more separate time intervals.
Phenolic
A rigid closed-cell foam product with an orange or light red foam core, sandwiched between various types of facers. Problems have been reported with board shrinkage, and corrosion of adjacent metal roof assembly components.
Picture Framing
A rectangular pattern of ridges in a roof membrane over insulation or deck joints.
Pitch Pocket
A flange, open bottomed, metal container placed around columns or other roof penetration that is filled with hot bitumen and/or flashing cement to seal the joint.
Ply
A layer of felt in a built up roof membrane system. A four-ply membrane system has four plies felt. The dimension of the exposed surface (the "exposure") of any ply may be computed by dividing the felt width (minus 2 inches) by the number of plies; thus, the exposed surface of a 36 inch wide felt in a four ply membrane should be 8 1/2 inches.
Pond
A roof surface that is incompletely drained.
Positive Drainage
The drainage condition in which consideration has been made for all loading deflection of the deck, and additional roof slop has been provided to ensure complete drainage of the roof area within 24 hours of rainfall.
Pourable Sealer
A type of sealant often supplied in two parts and is typically used to fill pitch pans.
Protected Membrane Roof (PMR)
An insulated and ballasted roof assembly, in which the membrane is covered by the insulation and ballasted (sometimes referred to as an "inverted roof assembly")
Psychometric Chart
A diagram relating to the properties of humid air with temperature.
Primer
A thin, liquid bitumen applied to a surface to improve the adhesion of subsequent application of bitumen.
Polyvinyl Chloride (PVC)
Usually associated with a thermoplastic single ply roof membrane system.
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