weathertightness

Weathertightness is the property of a building envelope to prevent water intrusion from weather, including rain, snow, and wind-driven spray. It covers all elements of the building shell—cladding, roofing, windows, doors, joints, penetrations, and the flashing and sealants that connect them. A weathertight enclosure resists typical service loads and environmental conditions such as temperature changes and aging. It relies on design, material choice, workmanship, and ongoing maintenance, and it interacts with, but is distinct from, air tightness and thermal performance.

Effective weathertight detailing creates a controlled path for water to shed or drain away, with a continuous drainage plane, proper flashing, and robust seals at openings and joints. Materials may include cladding with rain screens and resilient sealants. Movement joints and durability of flashing must accommodate expansion and contraction. Good installation and regular maintenance are essential to preserve performance.

Verification combines design review and testing, including visual inspections and water penetration tests where required. Standards vary by jurisdiction and may specify allowable water ingress under defined conditions. Addressing aging seals, flashing, and gaskets is part of lifecycle maintenance to sustain performance.

Failure can cause moisture damage, mold, and structural risk, and it affects energy efficiency and indoor comfort. Weathertightness is a key consideration in building codes and durability standards.