R Definitions

Definition Categories


R-value is a measure of a material’s resistance to conductive heat flow. R-value is the material’s insulating value. A higher R-value indicates higher resistance to conductive heat flow.  Only components designed to provide insulation, such as fiberglass batts and insulated sheathing, have an R-value for Chapter 11 purposes. Do not use any R-value for components such as drywall, structural sheathing, and siding when calculating the total R-value for an insulated assembly such as a wood-framed wall.


A rabbet is a groove or channel cut into material that is intended to receive another piece of rabbeted material. Two pieces of rabbeted material overlap to form a tight and water-resistive joint. A rabbet joint is normally used in interior and exterior trim work and in exterior siding. When used in exterior siding, the term shiplap is often used.



A raceway is a channel designed to enclose and protect electrical wires. Raceway is a generic term that describes conduit, tubing, surface raceways and other approved components through which electrical wires are run.


A receptacle is a device into which a plug is inserted and through which electricity flows to equipment that uses electricity. Receptacles include the familiar single (one plug) and duplex (two plug) 120 volt devices and the 240 volt devices most often seen in laundry rooms to serve electric clothes dryers. All receptacles are outlets but not all outlets contain receptacles. See the definition of outlet.

Receptor (indirect waste)

The term receptor refers to a device such as a floor sink or a floor drain. Indirect waste receptors have a source of water that is not directly and permanently connected to the receptor. Example: a floor drain could receive condensate water from an air conditioning system. The condensate drain is not directly and permanently connected to the floor drain. Shower pans are referred to in the IRC as shower receptors.


Resistance is a measure of how difficult it is for electricity to flow through a material. Electricity flows more easily (lower resistance) through a conductor and does not flow easily (higher resistance) through an insulator. Resistance is measured in ohms and is expressed in Ohm’s Law as the letter R.

Retaining Wall

A retaining wall is a structure that separates and holds back ground at a higher level from ground at a lower level. Retaining walls are not part of the structural support for a building. They are primarily used for landscaping and to adjust the level of sloped lots for easier building construction.


Brand name belonging to one manufacturer of NM cable.

Roof Span

The roof span is the total distance between supports for a roof system. Example: the span of a gable roof is the base of the triangle formed by each half of the gable