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
Sustainability in construction the carrying capacity of Earth . According to United Nations Environment Programme (UNEP), “"the increased construction activities and urbanization will increase waste which will eventually destroy natural resources and wild life habitats over 70% of land surface from now up to 2032." ” Moreover, construction uses around half of natural resources that humans consume. Production and transport of building materials consumes 25 - 50 percent of all energy used (depending on the country considered). Taking UK as a sample, the construction industry counts for 47% of CO2 emission, of which manufacturing of construction products and materials accounts for the largest