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A building envelope (or building envelope assembly) is the physical separator between the conditioned interior and the exterior environment, comprising exterior walls, roofs, floors on grade or over unconditioned space, windows, doors, and associated air, vapor, and moisture-control layers ^[1]. An energy-efficient building envelope is designed to reduce unwanted heat transfer, air leakage, and moisture accumulation while maintaining acceptable indoor environmental conditions. Key performance considerations include thermal resistance, airtightness, moisture control, solar control, and, where appropriate, thermal mass ^[1][2][3]. Thermal transmittance (U-value), expressed in W/(m²·K), can be calculated for applicable building components and elements from the thermal resistances of their constituent layers and the relevant surface resistances in accordance with ISO 6946 ^[4]. ISO 6946 applies principally to relevant building components and elements and excludes windows, doors and other glazed units, curtain walling, building components involving heat transfer to the ground, and components through which air is designed to permeate ^[4]. Energy-efficient envelopes are therefore defined by their ability to achieve appropriate thermal, air, moisture, and solar-control performance while supporting energy-efficient building operation, rather than by a prescribed material or construction method ^[1][2].