Thermal transmittance

Thermal transmittance, often represented by the symbol \( U \), is a measure of how well a building element (such as walls, roofs, windows, or doors) can conduct heat. It quantifies the rate of heat transfer through a unit area of the building element for a temperature difference of one degree (typically measured in watts per square meter per degree Kelvin, W/m²·K or W/m²·°C).