When it is colder on one side of an envelope element, such as a wall, roof, floor, or window, heat will conduct from the warmer side to the cooler side. Heat conduction is driven by temperature differences and is a major component of heating and cooling loads in buildings. Building codes address heat conduction by specifying minimum R-Values (thermal resistance to heat flow or insulation) or maximum U-Factors (the rate of steady-state heat flow) for building envelope construction assemblies.
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