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Architects and engineers call the resulting values either the U-Value or the R-Value of a construction assembly like a wall. Each type of value (R or U) are related as the inverse of each other such that R-Value = 1/U-Value and both are more fully understood through the concept of an overall heat transfer coefficient described in lower section ...
Although the concept of U-value (or U-factor) is universal, U-values can be expressed in different units. In most countries, U-value is expressed in SI units, as watts per square metre-kelvin: W/(m 2 ⋅K) In the United States, U-value is expressed as British thermal units (Btu) per hour-square feet-degrees Fahrenheit: Btu/(h⋅ft 2 ⋅°F)
The construction industry makes use of measures such as the R-value (resistance) and the U-value (transmittance or conductance). Although related to the thermal conductivity of a material used in an insulation product or assembly, R- and U-values are measured per unit area, and depend on the specified thickness of the product or assembly. [note 2]
The effectiveness of bulk insulation is commonly evaluated by its R-value, of which there are two – metric (SI) (with unit K⋅W −1 ⋅m 2) and US customary (with unit °F⋅ft 2 ⋅h/BTU), the former being 0.176 times the latter numerically, or the reciprocal quantity the thermal conductivity or U-value W⋅K −1 ⋅m −2.
Celotex Corporation is a defunct American manufacturer of insulation and construction materials. [ 1 ] [ 2 ] It was the subject of a number of high-profile lawsuits over products containing asbestos in the 1980s, eventually declaring Chapter 11 bankruptcy in 1990.
The U-value is used to refer to the amount of heat that can pass through a window, called thermal transmittance, with a lower score being better. [1] The U-factor of a window can often be found on the rating label of the window. Although the concept of U-value (or U-factor) is universal, U-values can be expressed in different units.
Base Value/Base Date 100 as of December 31, 1990 Calculation Frequency Every 15 seconds Date of Introduction Dow Jones-UBS Commodity Index: July 14, 1998.
The clo has the same dimensions as the R value (square metre kelvins per watt or m 2 ⋅K/W) used to describe insulation used in residential and commercial construction—thus, the higher the value, the better the insulation performance. 1 clo = 0.155 K·m 2 ·W −1 ≈ 0.88 K·m 2 ·BTU·W −1 ·ft −2 ·°F −1 ·hr −1 R.