Psychrometry. The branch of physics concerned with the
measurement or determination of atmospheric conditions,
particularly the moisture in air.
R-Value. In thermal insulation, the thermal resistance of
Re-covering. Covering an existing roof assembly with a new
membrane instead of removing the existing roof system before
installing the new membrane.
Edge of a roof at a gable.
Reglet. A horizontal groove in a wall or other vertical surface
for anchoring flashing.
Relative humidity. Ratio (expressed as percentage) of the mass
per unit volume (or partial pressure) or water vapor in an air-
vapor mixture to the saturated mass per unit volume (or partial
pressure) of the water vapor at the same temperature.
Unit of vapor-permeance resistance, reciprocal of perm.
Replacement. Process of removing and replacing an existing roof
system (as opposed to mere re-covering, see above), also called
The re-covering or replacement of an existing roof.
Resin. Basic raw material for manufacturing polymers, a
synthetic polymer containing no deliberately added ingredients.
Ridging. Membrane defect characterized by upward displacement of
the membrane, usually over insulation board joints (see Picture
Roll roofing. Coated felts, sometimes mineral-surfaced, supplied
in rolls and designed for use without field-applied surfacing.
Roofing contractor or subcontractor.
Roofing system. An assembly of interacting components designed
to weatherproof, and normally to insulate, a building's top
See Thermal Resistance.