| Summary: | Improving air tightness of structures prevents uncontrolled air leaks and it can be used to solve IAQ problems in buildings, usually in combination with other renovation methods. When improving air tightness, the airflow rates of mechanical ventilation usually need to be readjusted to correspond to the changed airtightness of the envelope. In optimal situation the supply- and exhaust air volumes are balanced and the pressure differential is close to zero Pascal. The article presents several buildings (n=7, built 1986-2005, renovated 2012-2019), where air tightness has been improved and the mechanical ventilation/pressure ratio has been adjusted as a part of other IAQ renovations. The pressure difference measurements (duration 7...14 days) have been done three times after renovation: right after the renovation, after 2 years and after 5 years. In addition, the long-term functionality of the air tightness renovation has been tested at the age of 5 years both with visual survey and with a tracer-gas leak test. After 5 years, the structures had remained airtight and the sealing materials were found to be durable. Pressure ratio needed some fine adjustment in 30 % of the renovated areas, where monitoring was made right after the renovation. At the age of 5 years the pressure ratio range was acceptable (-5...+5 Pa) and stable in approximately 85 % of the renovated areas. In these airtight buildings, the major effect to the pressure difference was caused by the mechanical ventilation system. Pressure difference adjustment and stability was possible to reach in all studied buildings with careful maintenance.
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