Wind comfort around buildings is measured by assessing how often wind speeds at pedestrian height exceed a defined threshold, typically 5 metres per second. The result is expressed as a probability — how many hours per year that threshold is crossed at a given location. Two widely used standards define what those probabilities mean in practice: the Dutch NEN 8100 standard and the international Lawson criteria. The sections below walk through the key questions around measurement methods, standards, and how the outcomes feed into design decisions.
What methods are used to measure wind comfort around buildings?
Wind comfort around buildings is measured using two main methods: physical wind tunnel testing and CFD (Computational Fluid Dynamics) simulations. Both assess wind speeds at pedestrian height across a range of wind directions, then combine those results with local meteorological data to calculate exceedance probabilities. The choice of method depends on project scale and complexity.
In a wind tunnel test, a scaled physical model of the building and its surroundings is placed in a controlled airflow environment. Sensors measure wind speeds at key locations around the model. This approach works well for individual buildings and smaller masterplan areas.
CFD simulations run the same calculations virtually. A detailed 3D model of the area is built from geodata, the surrounding airspace is divided into a computational mesh of cells, and airflow is solved mathematically across all wind directions. For large urban areas, CFD is the more practical option — a physical wind tunnel model of an entire city district simply is not feasible. In our wind engineering work, we use both methods depending on what the project calls for, and we regularly combine them for validation purposes.
Both methods feed their results into a statistical assessment. Wind speed data from simulations or tunnel tests is combined with meteorological wind statistics — in the Netherlands, this is typically based on KNMI data — to calculate how often specific wind speeds occur at each location throughout the year.
What are the Lawson criteria and the NEN 8100 standard?
The Lawson criteria and NEN 8100 are the two most widely used frameworks for classifying pedestrian wind comfort. Both use exceedance probabilities of wind speeds at eye height (1.75 m) to assign comfort classes, but they differ in thresholds, classification labels, and geographic application. NEN 8100 is the Dutch standard used in permit procedures in the Netherlands; the Lawson criteria are used internationally, including in the UK.
Under NEN 8100, wind comfort is classified from A to E based on how often wind speeds exceed 5 m/s at pedestrian height:
- Class A: exceedance less than 2.5% of hours per year — suitable for all activities including sitting
- Class B: 2.5–5% — good for walking, moderate for sitting
- Class C: 5–10% — moderate for slow walking, poor for sitting
- Class D: 10–20% — moderate for brisk walking only
- Class E: more than 20% — poor for all activities
NEN 8100 also defines a wind danger threshold at 15 m/s. An exceedance probability above 0.30% at that speed is considered unacceptable. Between 0.05% and 0.30%, danger may be conditionally accepted depending on the location and function.
The Lawson criteria follow a similar logic but use slightly different thresholds and activity categories. They are widely applied in the UK, Gibraltar, and other international contexts. We apply the Lawson criteria for projects outside the Netherlands, including our work in the UK and the Middle East.
How is pedestrian-level wind speed actually measured?
Pedestrian-level wind speed is measured at eye height, defined as 1.75 metres above ground level. In wind tunnel tests, pressure taps or anemometers placed at that height on the scale model capture speed and direction data at specific points. In CFD simulations, the computational mesh resolves airflow at that elevation across the entire study area, producing continuous spatial results rather than point measurements.
Field measurements — physical sensors placed at actual locations — are sometimes used to validate simulation results or to capture real-world conditions at a specific site. These are less common as a primary assessment tool because they only capture conditions during the measurement period, which may not represent the full range of wind conditions across a year.
What matters for the comfort assessment is not a single wind speed reading but the statistical distribution over time. Raw speed data is combined with local wind roses — diagrams showing how often wind comes from each direction and at what speed — to calculate how many hours per year a given threshold is exceeded at each point in the study area. This is what feeds into the NEN 8100 or Lawson classification.
What’s the difference between wind comfort and wind safety?
Wind comfort and wind safety address different risk levels. Wind comfort describes how pleasant or unpleasant conditions are for pedestrians going about normal activities — sitting, strolling, or walking purposefully. Wind safety (or wind danger) describes conditions where wind poses a physical risk to people, such as causing them to lose balance or be blown over. The two are assessed using different thresholds and carry different consequences for design.
Comfort is assessed at the 5 m/s threshold. Locations that exceed this speed too frequently receive a lower comfort class, which may be unacceptable depending on the intended use of the space. A terrace classified as D or E is uncomfortable but not inherently dangerous.
Safety is assessed at 15 m/s. Under NEN 8100, an exceedance probability above 0.30% at this speed is classified as dangerous and is generally unacceptable regardless of location. Between 0.05% and 0.30%, the situation is described as “limited risk” and may be conditionally accepted. Locations like exposed bridges — the Erasmus Bridge in Rotterdam is a well-documented example — can reach a danger classification even when the surrounding area scores well on comfort.
In practice, a location can be perfectly safe but still uncomfortable, or it can be comfortable most of the time but occasionally hazardous during storms. Both dimensions need to be assessed separately in a complete wind study.
When is a wind comfort study legally required?
In the Netherlands, a wind comfort study is legally required when a building project triggers a permit procedure and the municipality or reviewing authority determines that wind impact needs to be assessed. This is most common for high-rise buildings, large-scale developments, and projects in exposed locations. NEN 8100 is the applicable standard for these assessments, and its results must be defensible in the context of the permit review.
There is no single national rule that specifies exactly which building height or footprint triggers a mandatory study. In practice, municipalities set their own thresholds and policies. Buildings taller than roughly twice the height of their surroundings are more likely to require a study, as they create stronger downwash effects and increase wind speeds at street level. Developments on open or waterfront sites face similar scrutiny.
Beyond legal requirements, wind comfort studies are also carried out proactively — to validate a design before committing to it, to identify wind issues early enough to address them through design changes, or to provide evidence when a planning authority raises concerns. Finding a wind problem late in the design process is significantly more expensive than addressing it at concept stage, which is why many developers commission an assessment well before the permit phase.
How do wind comfort results influence building design?
Wind comfort results directly inform design decisions about building shape, orientation, height transitions, and the layout of public spaces. When results show that certain locations receive poor comfort classifications, designers can use the findings to test and compare mitigation measures before construction begins.
Common design responses include:
- Setbacks: stepping back upper floors reduces downwash at street level; a minimum depth of around 5 metres is effective for buildings of approximately 100 metres in height
- Clustering: grouping towers so they shelter each other, limiting height differences between adjacent buildings to around 30%
- Facade orientation: avoiding the widest facade perpendicular to the prevailing wind direction
- Covered walkways: providing direct protection for pedestrians at ground level
- Planting and screens: effective for comfort improvement in public spaces, though not as a primary safety measure
The most important principle is that wind problems are far easier to address at the urban planning level than at the individual building level. Once a building’s position and massing are fixed, the options narrow considerably. Results from CFD simulations are typically presented as colour-coded maps showing comfort classes across the study area — these make it straightforward to identify problem locations and communicate findings to architects, planners, and permit authorities.
How Actiflow helps with wind comfort assessment
We carry out pedestrian wind comfort assessments for a wide range of projects — from individual high-rise buildings to city-wide studies like the comprehensive wind assessment we delivered for the city of Rotterdam. With over 21 years of experience and deep familiarity with NEN 8100 and the Lawson criteria, we know what municipalities expect and how to produce reports that hold up under scrutiny.
- Wind comfort assessments using CFD simulations and wind tunnel testing, classified to NEN 8100 or Lawson criteria
- Colour-coded output maps and visualisations ready to submit to permit authorities or share with clients
- Wind danger assessments at the 15 m/s threshold alongside comfort classification
- Design consultancy: we help you interpret results and identify mitigation measures that work
- Fast turnaround — for regular clients, we can start the next day if the project requires it
- Experience across the Netherlands, Belgium, the UK, Gibraltar, and beyond
Want to know more about how we work? Visit our about us page for background on our team and approach.
Curious how we can help with wind comfort for your project? Feel free to contact us. We would be happy to discuss your project and help you find the right engineering solution.
