windtightness

Windtightness is the ability of a building’s enclosing structure to resist wind-driven air infiltration and exfiltration. It is a key aspect of the overall airtightness of a building envelope, influencing heat loss, comfort, and moisture transport. Achieving windtightness involves continuous air barriers and careful detailing around joints, openings, and penetrations in walls and roofs, as well as around windows, doors, and service penetrations. Materials commonly used include membranes, tapes, sealants, gaskets, and sprayed foams, installed to minimize uncontrolled air leakage while allowing intentional ventilation where needed.

Measurement and standards: Windtightness is typically assessed with a blower-door test that measures the air leakage rate at a fixed pressure, commonly 50 pascals. Results are expressed as air changes per hour at 50 Pa (ACH50) or as a normalized leakage rate. Standards such as ISO 9972 and EN 13829 are used in many regions, with national building codes setting target values that vary by climate and building type.

Factors and strategies: Leakage pathways arise from gaps at joints, corners, around windows and doors, and at penetrations for pipes and cables, as well as from poor construction quality. Strategies to improve windtightness include using continuous air barriers on either the exterior or interior, meticulous detailing at roof-to-wall and wall-to-foundation transitions, proper window and door installation with seals, and careful sealing of penetrations and mechanical services.

Implications: Adequate windtightness reduces energy use and drafts but must be paired with controlled ventilation to maintain indoor air quality and manage moisture. Excessive airtightness without ventilation can lead to condensation, mold, and poor indoor air quality. Retrofit measures often focus on improving windtightness through targeted sealing and barrier upgrades.