Tall buildings accelerate wind at street level because they act as barriers that deflect fast-moving air from higher altitudes downward toward the ground. The taller a building is relative to its surroundings, the stronger this effect becomes. Below, we answer the most common questions about how high-rise buildings affect pedestrian wind comfort and what you can do about it.
Why do tall buildings accelerate wind at street level?
Tall buildings accelerate wind at street level by forcing high-altitude air, which moves faster than air near the ground, downward along their facades. When this downdraft reaches the ground, it spreads out horizontally and creates localised zones of high wind speed that pedestrians experience as sudden gusts. The taller the building and the greater its height difference from surrounding structures, the stronger this effect.
At higher altitudes, wind speed increases because there is less friction from the ground and surrounding objects. A tall building interrupts this faster-moving air and redirects it downward. This is sometimes called a downdraft effect, and it can produce wind speeds at pavement level that are two to three times higher than you would normally expect in that location.
A useful rule of thumb: a building that is more than twice the height of its immediate surroundings is significantly more likely to cause wind problems at street level. The height difference between adjacent buildings also matters. Keeping that difference below 30% reduces the risk of severe downdraft effects, which is why well-planned high-rise clusters tend to perform better than isolated towers.
What types of wind effects do high-rise buildings cause?
High-rise buildings cause several distinct types of wind effects at pedestrian level. The most common are the downdraft effect (fast air pushed down along the facade), the corner acceleration effect (wind speeding up as it wraps around building corners), and the channelling effect (wind funnelled and accelerated through narrow gaps between buildings or along streets).
Each of these effects has a different character and affects different locations around the building:
- Downdraft: Occurs on the windward side of the building, where high-altitude air is pushed downward and hits the ground directly in front of the facade.
- Corner acceleration: Wind that deflects around the building edges speeds up significantly at the corners, creating uncomfortable or even dangerous conditions on the sides of the building.
- Channelling: When streets run parallel to the dominant wind direction, or when gaps between buildings align with the wind, air accelerates through those corridors like water through a narrowing pipe.
- Wake turbulence: On the leeward side of the building, airflow becomes chaotic and gusty as the wind reattaches after passing the structure.
Understanding which effect is dominant at a specific location is important because each requires a different mitigation approach. A canopy helps with downdraft but does nothing for corner acceleration, for example.
Which areas around a tall building are most affected?
The areas most affected by wind around a tall building are the windward facade at ground level, the building corners, and any open plazas or passageways directly adjacent to the structure. These are the locations where wind speeds are typically highest and where pedestrian discomfort or safety risks are most likely to occur.
More specifically, the risk is highest in these situations:
- Open plazas on the windward side: When more than 25% of the windward facade faces an open area, the chance of significant wind nuisance increases sharply.
- Passageways and through-building openings: Any opening aligned with the dominant wind direction creates a pressure shortcut that dramatically accelerates airflow.
- Building corners: These are almost always acceleration zones, regardless of building shape.
- Areas next to isolated towers: A tower surrounded by low-rise buildings has no neighbouring structures to absorb or deflect wind, so the full downdraft reaches street level unimpeded.
Real-world examples confirm this pattern. In Rotterdam, areas directly adjacent to the Lloyd Tower, which stands around 70 metres tall in a predominantly low-rise industrial context, experience persistent downdraft effects at pedestrian level. The surrounding low-rise buildings offer no protection, and the prevailing south-westerly wind arrives largely unobstructed from the river and the Waalhaven. For more on how wind engineering addresses these site-specific risks, the methodology matters as much as the location.
How does building shape influence pedestrian wind comfort?
Building shape has a direct influence on pedestrian wind comfort. Rounded or tapered facades allow wind to flow around the structure more smoothly, reducing the strength of downdrafts and corner effects. Flat, wide facades oriented perpendicular to the dominant wind direction produce the worst conditions because they intercept the maximum amount of air and redirect it downward with full force.
Several shape-related factors determine how much wind a building generates at street level:
- Facade orientation: Placing the widest facade parallel to the dominant wind direction rather than perpendicular to it significantly reduces wind impact.
- Setbacks: Stepping the building back at lower floors breaks up the downdraft before it reaches the ground. For a building of around 100 metres, a setback of at least 5 metres is needed to be effective. However, the roof level of the setback itself sits in the downdraft zone and is not suitable as an outdoor terrace or amenity space.
- Tapered or rounded profiles: These guide airflow along the building surface rather than forcing it downward, which reduces ground-level wind speeds.
- Canopies: These are less effective than setbacks because they only relocate the downdraft to the canopy edge rather than eliminating it.
Shape decisions made early in the design process have the biggest impact. Once a building’s massing and orientation are fixed, correcting wind problems becomes much harder and more expensive.
When is a pedestrian wind comfort study required for a tall building?
A pedestrian wind comfort study is typically required when a tall building is likely to significantly change wind conditions in a publicly accessible area. In the Netherlands, this is assessed against the NEN 8100 standard, which classifies wind conditions from Class A (comfortable) to Class E (dangerous). Many municipalities require a wind study as part of the permit application when a building exceeds a certain height or is located in a sensitive urban environment.
In practice, a wind study is needed in these situations:
- The building is significantly taller than its surroundings, particularly when it is more than twice the height of nearby structures.
- The project involves public spaces such as plazas, entrances, or outdoor seating areas adjacent to the building.
- The municipality or planning authority explicitly requests one as a condition of the permit.
- The architect or developer wants to validate the design before committing to a layout that may later require costly revisions.
For projects outside the Netherlands, the Lawson criteria are the most widely used international standard. Both NEN 8100 and Lawson classify wind conditions based on the probability of exceeding threshold wind speeds for different activity types, from walking and cycling to sitting and standing. Knowing which standard applies to your project early on saves time and avoids having to redo assessments in a different format later. You can find an overview of both approaches on the Actiflow website.
How can wind comfort problems around tall buildings be fixed?
Wind comfort problems around tall buildings can be fixed using a hierarchy of measures, ranging from changes to the building’s massing and orientation at the top, through facade-level interventions, to landscaping and public space adjustments at the bottom. The earlier in the design process these measures are applied, the more effective and cost-efficient they are.
Here is how the hierarchy works in practice:
- Urban planning level: Cluster towers so they shelter each other. Keep height differences between adjacent buildings below 30%. Orient streets diagonally or perpendicular to the dominant wind direction to avoid channelling. This is the most effective level of intervention.
- Building volume and orientation: Align the widest facade parallel to the dominant wind direction. Avoid passageways or openings that face the prevailing wind. Add setbacks of at least 5 metres at lower floors for buildings around 100 metres tall.
- Facade-level measures: Use rounded or tapered profiles to guide airflow along the building. Add canopies where setbacks are not possible, bearing in mind that canopies only shift the problem rather than solve it.
- Ground-level measures: Use screens or barriers to redirect local airflow. Plant trees or hedges to slow wind, though deciduous trees lose their leaves in winter when wind speeds are highest. Adjust the function of the most exposed locations: avoid placing entrances, terraces, playgrounds, or seating in the windiest spots.
One important principle: solving wind problems at building level is much harder if wind has not been considered at the urban planning level first. The most effective projects integrate wind thinking from the earliest design phases, not as a last-minute check before permit submission.
How Actiflow helps with wind comfort around tall buildings
We work with architects, developers, structural engineers, and municipalities to assess and improve pedestrian wind comfort around tall buildings. With over 21 years of experience and roots in Delft University of Technology’s aerospace engineering faculty, we combine deep technical expertise with practical knowledge of what municipalities actually need from a wind study.
- Pedestrian wind comfort assessments using CFD simulations and wind tunnel tests, classified against NEN 8100 (Netherlands) or Lawson criteria (international projects including the UK, Gibraltar, and the Middle East).
- Clear, visual output including colour-coded maps and graphics that you can present directly to clients, planners, and permit authorities without translation.
- Design consultancy from early massing studies through to final permit documentation, so wind issues are caught before they become costly revisions.
- City-wide and area studies for large-scale masterplan assessments, including the comprehensive wind study we carried out for the city of Rotterdam.
- Fast turnaround for regular clients, we can start the next day if needed, and our internal automation keeps delivery times short without compromising quality.
Curious how we can help with wind comfort around your project? Contact us and we will be happy to discuss what type of study fits your situation. You can also learn more about us and how we work.
