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U-Value
STRUCTURE & PHYSICSintermediate
Definition
A measure of how much heat passes through a building element (wall, roof, floor, or window) per unit area, per degree of temperature difference — expressed in W/m²K. The lower the U-value, the better the insulation. Building regulations specify maximum U-values for new construction; Passive House standards require much lower values.
Example
A standard double-glazed window might have a U-value of 1.6 W/m²K; a triple-glazed Passive House window achieves 0.8 or below — halving the heat lost through the same area of glass.