{"id":9948,"key":"R_value","title":"R value","latest":{"id":1207651,"timestamp":"2025-11-27T22:37:49Z"},"content_model":"wikitext","license":{"url":"https://www.appropedia.org/Appropedia:Copyrights","title":"CC-BY-SA-4.0"},"source":"{{Topic notice}}\n\nThe materials ability to resist the [[heat transfer]] by [[conduction]] is known as thermal resistance or R-Value. Materials with high R-values have greater insulating capabilities than materials with low R-value numbers. Most construction materials have easy to find R-values, such as insulation you may find at a local hardware store may have R-values ranging from R-19 to R-32. As it would be expected the R-32 insulation has better insulation capabilities than the R-19, but the R-32 is usually more expensive.\n\n== Definitions ==\n\nR-values can be expressed using basic thermodynamic properties of heat transfer, conductivity and amount of material in question:\n\nSine R-values are \"A measure of the resistance of the material to heat flow is the thermal resistance R, often called its R-value given by R=delta/k. The higher the R-value is, the better are the insulating properties of the material. Using this notation, the rate of heat flow is given by\n Qc/t = 1/R*A*change in T\nwhere;\n\n* R is a function of both the type of material and its thickness.\n* T=Time\n* Qc=Heat transfer\n* AL/k = R-value of insulation\n\nR-value according to Physics by Cutnell and Johnson:\n\n* The R value expresses in a single number the combined effects of thermal conductivity and thickness.\n* Larger R values reduce the heat per unit time flowing through the material and therefore mean better insulation. It also convenient to use R values to describe layered slabs formed by sandwiching together a number of materials with different thermal ratings and different thicknesses. The R-values for the individual layers can be added to give a single R-value for the entire slab. It should be noted, however, that R-values are expressed using units of feet, hours, F and BTU for thickness, time, temperature, and heat, respectively.\n\nAccording to the [http://web.archive.org/web/20121027045557/http://www.engext.ksu.edu:80/ees/henergy/envelope/basement.html Kansas State University Extension Service] the R-value of soil is about 1 per foot.\n\n== See also ==\n\n* [[Thermal mass]]\n* Earth sheltering\n\n== External links ==\n\n* [[Wikipedia:R value]]\n\n{{Page data\n| license = CC-BY-SA-3.0\n| part-of = PH261\n| keywords = Heating and cooling, Thermal insulation, energy efficiency, construction, heating, cooling\n| sdg = SDG07 Affordable and clean energy\n| organizations = Clarion University\n| description = Understand R-value and how it affects insulation. Appropedia explains it simply so you can save energy and stay comfortable.\n}}\n\n[[Category:Heating and cooling]]\n[[Category:Energy efficiency]]\n[[Category:Construction]]"}