What is "r-value"

n. Resistance-value - A measure of thermal resistance used in domestic insulation.

The R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux ( heat transfer per unit area per unit time, $\dot Q_A$) through it or $R = \Delta T/\dot Q_A$. Thermal resistance varies with temperature but it is common practice in construction to treat it as a constant value.

An R-value is a unit of thermal resistance for a particular material or assembly of materials (such as an insulation panel). The R-value depends on a solid material's resistance to conductive heat transfer. For loose or porous material, the R-value accounts for convective and radiative heat transfer through the material. However it does not account for the radiative or convective properties of the material's surface, which may be an important factor for some applications.

R is expressed as the thickness of the material normalized to the thermal conductivity. The unit thermal conductance of a material is the reciprocal of the unit thermal resistance. This can also be called the unit surface conductance. The higher the value of R, the better the building insulation's theoretical effectiveness.

R-value is the reciprocal of U-factor.

The R-Value test, California Test 301, measures the response of a compacted sample of soil or aggregate to a vertically applied pressure under specific conditions. This test is used by Caltrans for pavement design, replacing the California bearing ratio test. Many other agencies have adopted the California pavement design method, and specify R-Value testing for subgrade soils and road aggregates.

The test method states:

The R-value of a material is determined when the material is in a state of saturation such that water will be exuded from the compacted test specimen when a 16.8 kN load (2.07 MPa) is applied. Since it is not always possible to prepare a test specimen that will exude water at the specified load, it is necessary to test a series of specimens prepared at different moisture contents.

R-Value is used in pavement design, with the thickness of each layer dependent on the R-value of the layer below and the expected level of traffic loading, expressed as a Traffic Index. Details of the pavement design procedure are given in Chapter 600 of the California Highway Design Manual.

Category:Soil tests

R-value or rvalue may refer to:

• In computer science, a value considered independently of its storage location
• R-value (insulation) in building engineering, the efficiency of insulation of a house
• R-value (soils) in geotechnical engineering, the stability of soils and aggregates for pavement construction
• R-factor (crystallography), a measure of the agreement between the crystallographic model and the diffraction data
• In statistics, the Pearson product-moment correlation coefficient, or simply correlation coefficient
• In ophthalmic optics, the distance between the segment optical center and the segment top
• In solid mechanics, the Lankford coefficient