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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 ...
All thermal insulation requirements in ASHRAE 90.1 are divided by the climate zone, it means that the amount of insulation needed for a building is determined by which climate zone the building locates. The thermal insulation requirements are shown as R-value and continuous insulation R-value as the second index. [13]
Unscrupulous contractors may "fluff" insulation using fewer bags than optimal for a desired R-value. Dry-spray (but not wet-spray) cellulose can settle 20% of its original volume. [28] However, the expected settling is included in the stated R-Value. The dense-pack dry installation reduces settling and increases R-value.
Warm air rises, so ceiling insulation is designed to have a higher r-value and the insulation is often installed between the ceiling joists or rafters. A properly insulated and ventilated roof is called a cold roof. A warm roof is a roof that is not ventilated, [9] where the insulation is placed in line with the roof pitch. [10]
This means that VIPs have about one-fifth the thermal conductivity of conventional insulation, and therefore about five times the thermal resistance per unit thickness. Based on a typical k-value of 0.007 W/(m·K), the R-value of a typical 25-millimetre-thick (1 in) VIP would be 3.5 m 2 ·K/W (20 h·ft 2 ·°F/BTU). To provide the same R-value ...
EPS is the most common of the foams used and has an R-value (thermal resistance) of about 4 °F·ft 2 ·h/Btu (equivalent to about 0.7 K·m 2 /W) per 25 mm thickness, which would give the 3.5 inches (89 mm) of foam in a 4.5-inch-thick (110 mm) panel an R value of 13.8 (caution: extrapolating R-values over thickness may be imprecise due to non ...
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