Loopshore Oy carried out pressure difference measurements in a block of flats in Tampere. The findings showed significant negative pressure in one particular flat – but why there of all places?
Background and measurement site
The study covered a fifth-floor flat in a housing company and the building's first-floor club room. The aim was to measure pressure differences between indoor and outdoor air and to investigate possible problems related to ventilation and the airtightness of the structures.
The measurements were made with Loop Delta devices, which collected continuous time-series data for a week. This made it possible to build a statistically reliable picture of the pressure conditions.
Result: strong negative pressure in the flat relative to both outdoor air and the stairwell
The fifth-floor flat was under constant negative pressure:
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Relative to outdoor air, the pressure difference averaged −10.2 Pa (range −14.0 … −4.7 Pa).
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Relative to the stairwell, the pressure difference averaged −11.9 Pa, exceeding the recommended limit of −10 Pa.
This means that the flat was drawing replacement air both from outside and from the stairwell – and from the latter, possibly also impurities or odours from other flats and shared spaces.
What was particularly surprising was that the flat was on an upper floor, where the stack effect normally causes slight positive pressure relative to the stairwell. Negative pressure this strong points to unbalanced ventilation or an insufficient supply of replacement air.
Point of comparison: the club room
Pressure differences in the first-floor club room were considerably more moderate (averaging −3.7 Pa), and at times the space was even under slight positive pressure. This is consistent with the fact that the ventilation can be adjusted to match usage times.
How weather affects pressure differences
Weather conditions, especially wind speed and direction, proved to be a significant variable. Stronger negative pressure peaks were observed during windy periods. In addition, temperature differences between indoor and outdoor air probably played a part in amplifying the stack effect.
Recommendations and next steps
Based on the report, the following were recommended:
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Balancing the flat's ventilation
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Checking the replacement air routes and adding more if necessary
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Mapping air leaks, particularly from the direction of the stairwell
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Checking that the stairwell ventilation is working properly
Excessive negative pressure is not just a question of energy efficiency or comfort – it can lead to harmful airflows, moisture moving into the structures and poorer indoor air quality.
Why is continuous measurement needed?
Pressure differences clearly follow a daily rhythm and vary with the weather. A single spot check is not enough to build a comprehensive picture. That is exactly why time-series data from Loop Delta makes it possible to identify problems and understand their causes from the perspective of both building physics and building use.
Loopshore Oy provides solutions for managing ventilation and airtightness in buildings – by measuring and understanding.