| 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). The formula for perm is: P
= GRAINS OF WATER VAPOR/SQUARE FOOT * HOUR * INCH MERCURY |
| Permeance |
an index of a material's resistance
to water vapor transmission. (See PERM. ) |
| 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. (Contact IRC staff for further
information and details.) |
| 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. |
| Plastic Cement |
see FLASHING CEMENT |
| 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. (See EXPOSURE.) |
| 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. |
| PVC |
Polyvinyl Chloride - Usually
associated with a thermoplastic single ply roof membrane
system. |
