U-Value

U-value is the reciprocal of R-value (thermal resistance). For commercial buildings in tropical climates, wall U-values of 0.5-1.0 W/m2K and roof U-values of 0.3-0.5 W/m2K are considered good practice. Window U-values range from 1.5 W/m2K (high-performance double glazed) to 5.8 W/m2K (single glazed). ASHRAE 90.1 and BNBC specify maximum U-values by climate zone and building element.

Building envelope thermal performance directly impacts cooling energy consumption. In hot climates like Bangladesh, poor insulation (high U-values) increases cooling loads by 20-40%. U-values are a key input for energy modelling and audit calculations.