Tall buildings face particular challenges when it comes to ventilation and energy efficiency. One of the most significant – and often invisible – is the pressure difference across the building envelope, which can have a major impact on indoor air quality, energy consumption and the condition of the structures.
Thermal pressure difference: the stack effect in everyday life
When it is freezing outside and warm inside, a natural phenomenon occurs: warm air tends to rise and escape from the upper parts of the building, while cold outdoor air flows in at the lower parts. This is called the thermal pressure difference, or stack effect. The phenomenon is particularly pronounced in winter and increases with the height of the building and the temperature difference.
For example, in a 50-metre building where indoor and outdoor temperatures differ by 40 °C, pressure differences of as much as ±20 pascals can arise. This can cause significant leakage airflows that impair ventilation performance and may carry moisture into the structures.
How wind affects pressure differences
Wind striking the outer surface of a building creates positive pressure on the windward side and negative pressure on the opposite side. When wind speed exceeds 10 m/s, its effect can outweigh thermal pressure differences and cause strong airflows through the envelope. Tall buildings in particular, which are exposed to pressures that vary from several directions, are prone to this kind of phenomenon.
Uncontrolled airflows – an invisible risk
The combined effect of pressure differences can cause leakage airflows that bypass the intended ventilation routes. This disturbs the building's internal pressure and airflow balance. The consequences can include:
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Ineffective ventilation, when the designed airflows are not achieved
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Increased energy consumption, as heat is lost in an uncontrolled way
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Risk of moisture damage, as moisture from outdoor air can penetrate the structures
How can pressure differences be managed?
Managing pressure differences calls for a holistic approach:
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An airtight building envelope and internal structures prevent uncontrolled air leakage
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Balanced ventilation ensures that air flows along the intended routes
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Compartmentation (e.g. stairwell separation, draught lobbies) limits the spread of pressure differences
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Structural solutions such as revolving doors and airlocks prevent pressure transfer between spaces
In addition, up-to-date measurement and continuous monitoring are needed. Without accurate information on the pressure differences between the outdoors and the indoor spaces, there is no way of knowing how the building actually performs in different weather conditions.
Are you in control of the pressure conditions in your building?
Loopshore offers a simple, continuously measuring solution for managing pressure differences. Real-time monitoring of outdoor and indoor pressure helps to identify problems, improve ventilation performance and reduce moisture risks – especially in tall buildings and changing weather conditions.