R-value (insulation) as ASHRAE 90.1 and the IECC prescribe U-values. However, R-value is widely used in practice to describe the thermal resistance of insulation products, layers, and most other parts of the building enclosure (walls, floors, roofs). Other areas of the world more commonly use U-value/U-factor for elements of the entire building enclosure including windows, doors, walls, roof, and ground slabs. The SI (metric) unit of R-value is whereas the I-P (inch-pound) unit is For R-values there is no difference between US customary units and imperial units, so the same I-P unit is used in both. Some sources use ″RSI″ when referring
R-value (insulation) it does not produce any quantitative data. This method can only be used to approximate the U-value or the inverse R-value. This approach is based on three or more temperature measurements inside and outside of a building element. By synchronizing these measurements and making some basic assumptions, it is possible to calculate the heat flux indirectly, and thus deriving the U-value of a building element. The following requirements have to be fulfilled for reliable results: The U-value can be calculated as well by using a heat flux sensor in combination with two temperature sensors. By measuring the heat that is