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The R-value is the building industry term [3] for thermal resistance "per unit area." [4] It is sometimes denoted RSI-value if the SI units are used. [5] An R-value can be given for a material (e.g., for polyethylene foam), or for an assembly of materials (e.g., a wall or a window). In the case of materials, it is often expressed in terms of R ...
Energy-efficient houses in cold climates often feature triple-glazed windows with a U-value between 0.19 and 0.26. In moderate and hot climates, quality double-glazed windows with a U-value of about 0.30 are generally a more cost-competitive and effective choice. [8]
A typical installation of insulated glass windows with uPVC frames. Possibly the earliest use of double glazing was in Siberia, where it was observed by Henry Seebohm in 1877 as an established necessity in the Yeniseysk area where the bitterly cold winter temperatures regularly fall below -50° C, indicating how the concept may have started: [2]
Typical R-values are given for various materials and structures as approximations based on the average of available figures and are sorted by lowest value. R-value at 1 m gives R-values normalised to a 1 metre (3 ft 3 in) thickness and sorts by median value of the range.
Thermal insulance (R-value) is a measure of a material's resistance to the heat current. It quantifies how effectively a material can resist the transfer of heat through conduction, convection, and radiation.
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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)
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