There are five main wind comfort criteria for pedestrians, each defined by a specific activity and the wind speed threshold at which conditions become uncomfortable for that activity. The two most widely used frameworks are the Lawson criteria (used in the UK, Canada, and internationally) and the NEN 8100 standard (used in the Netherlands). Both classify wind conditions on a scale from comfortable to dangerous, but they use different thresholds and methods to get there. This article walks through each criterion, explains how the two frameworks compare, and helps you figure out which one applies to your project.
How do wind comfort criteria actually classify wind conditions?
Wind comfort criteria classify pedestrian wind conditions by measuring how often wind speeds at eye level exceed a defined threshold for a specific activity. The core principle is simple: different activities tolerate different wind speeds, and the more often those speeds are exceeded, the worse the comfort class assigned to that location.
Both the Lawson criteria and NEN 8100 measure wind speed at eye height (1.75 metres) and express exceedance as a probability — how many hours per year, or what percentage of the time, wind speeds go above the relevant threshold. A busy entrance plaza used for standing and socialising has a stricter threshold than a through-route where people are just walking past.
The five main activity categories that wind comfort criteria assess are:
- Sitting (outdoor seating, terraces, rest areas)
- Standing (bus stops, entrances, waiting areas)
- Strolling (leisurely walking, window shopping)
- Walking through (purposeful pedestrian movement)
- Dangerous / unsafe (conditions posing a physical risk)
Each of these maps to a wind speed threshold. Exceed that threshold too often, and the location fails its comfort class for that activity. This is the foundation shared by both major frameworks — though they set those thresholds differently.
What are the Lawson criteria for pedestrian wind comfort?
The Lawson criteria define pedestrian wind comfort by setting a maximum wind speed for each activity that must not be exceeded more than 5% of the time. Developed in the UK and widely adopted in Canada and internationally, Lawson assigns a comfort class based on the intended use of a space and whether measured wind speeds stay within the permitted exceedance limit.
The Lawson thresholds work as follows:
- Sitting: wind speeds above 4 m/s must not occur more than 5% of the time
- Standing: wind speeds above 6 m/s must not occur more than 5% of the time
- Strolling: wind speeds above 8 m/s must not occur more than 5% of the time
- Walking through: wind speeds above 10 m/s must not occur more than 5% of the time
- Uncomfortable: wind speeds above 10 m/s exceed the 5% threshold — the location fails for all pedestrian use
Lawson also includes a wind danger threshold: speeds above 15 m/s occurring more than 0.025% of the time indicate a risk for vulnerable people, while speeds above 20 m/s at the same exceedance level represent a risk for everyone.
One important limitation of Lawson in practice: the thresholds are relatively generous. In the Rotterdam pilot study we conducted, the Lawson method classified the Erasmusbrug as the only problematic location — while multiple other spots in the city are clearly uncomfortable in reality. This is because Lawson’s higher speed thresholds mean more locations pass than NEN 8100 would classify as acceptable.
For wind engineering projects in the UK, Gibraltar, and other international contexts, Lawson remains the standard reference framework.
What is the NEN 8100 standard and how does it differ from Lawson?
NEN 8100 is the Dutch standard for pedestrian wind comfort, and it differs from Lawson primarily in how it measures exceedance and how finely it grades the results. Where Lawson uses a single 5% exceedance threshold across all activities, NEN 8100 assigns locations to one of five comfort classes (A through E) based on the probability that wind speeds exceed 5 m/s at eye level.
The NEN 8100 classification table looks like this:
- Class A: exceedance below 2.5% (under 219 hours per year) — good for sitting, strolling, and walking through
- Class B: 2.5–5% exceedance (219–438 hours per year) — good for sitting and strolling, moderate for walking through
- Class C: 5–10% exceedance (438–876 hours per year) — good for sitting, moderate for strolling, poor for walking through
- Class D: 10–20% exceedance (876–1,752 hours per year) — moderate for sitting, poor for strolling and walking through
- Class E: exceedance above 20% (over 1,752 hours per year) — poor for all activities
The key practical difference: NEN 8100 is more nuanced in the worst-performing classes and aligns more closely with what people actually experience on the ground. It also applies a single measurement threshold (5 m/s) across all activity types, which makes it easier to produce consistent, comparable results across a study area. For projects in the Netherlands, NEN 8100 is the regulatory standard — municipalities and permit authorities expect results in this format.
What wind speed thresholds define danger versus discomfort?
Discomfort and danger are measured differently. Discomfort is about wind speeds that make a space unpleasant to use — conditions that exceed the activity threshold too often. Danger is about wind speeds that pose a physical safety risk, regardless of how often they occur.
Under NEN 8100, wind danger is assessed separately from comfort:
- Limited risk: wind speeds above 15 m/s occurring between 0.05% and 0.30% of the time (4.5 to 26 hours per year) — sometimes acceptable depending on location
- Dangerous: wind speeds above 15 m/s occurring more than 0.30% of the time (over 26 hours per year) — unacceptable under any circumstances
Under Lawson, the danger thresholds are:
- Above 15 m/s more than 0.025% of the time — risk for vulnerable pedestrians
- Above 20 m/s more than 0.025% of the time — risk for all pedestrians
In practical terms, locations that reach the danger threshold are rare but serious. Known examples include exposed bridge structures and the areas directly beside tall, freestanding towers where downwash streams reach ground level. The area next to Rotterdam’s Lloyd Tower (70 metres high) is a documented case where downward airflow reaches pedestrian level and creates genuine wind danger.
Which wind comfort criterion applies to a building project?
The answer depends on where your project is located and what the permit authority requires. For projects in the Netherlands, NEN 8100 is the applicable standard — it is what municipalities and planning authorities expect, and it is the framework used to assess whether a location meets the required comfort class for its intended use. For projects in the UK, Canada, or other international contexts, the Lawson criteria are the standard reference.
Beyond geography, the choice of method also depends on project scale. Wind tunnel testing is well suited to individual buildings and smaller masterplans. For large-scale urban or area-wide studies, CFD simulations are the appropriate method — a physical wind tunnel simply cannot handle the model size required for a city district or waterfront development.
A practical rule of thumb: if your project is a single high-rise in Amsterdam, you need a NEN 8100 assessment using CFD or wind tunnel testing. If it is a mixed-use development in London, you need Lawson. If it spans multiple countries or involves an international client, it is worth confirming with your consultant which framework the local authority will accept before commissioning the study.
One more factor worth knowing: the intended use of the space determines what comfort class is required. A public square with outdoor seating needs to meet Class A or B. A service route or maintenance access path has a lower bar. Getting the activity classification right from the start avoids surprises when the results come in.
How do wind comfort results affect building design decisions?
Wind comfort results directly inform which design changes are needed — and how urgent they are. A location that scores Class D or E under NEN 8100, or fails Lawson’s threshold for its intended activity, typically requires intervention before a permit is granted. The earlier in the design process you have this information, the cheaper and less disruptive the fix.
Common design responses, ranked from most to least effective, include:
- Urban planning level: clustering towers so they shelter each other, keeping height differences between adjacent buildings below 30%, and orienting streets diagonally rather than parallel to the prevailing wind direction
- Building volume and orientation: avoiding the widest facade facing the dominant wind direction, minimising through-passages aligned with prevailing wind, and adding setbacks (at least 5 metres deep for a building of around 100 metres)
- Architectural features: rounded or tapered facades that guide airflow around the building rather than downward, covered walkways at least 5 metres deep, and canopies (though canopies are less effective than setbacks — they shift the downwash to the canopy edge rather than eliminating it)
- Public space adaptations: planting, sunken seating areas, and relocating sensitive functions like playgrounds and terraces away from the windiest spots
The important principle here: wind problems are much harder to solve at building level if wind has not been considered at the urban planning level first. Discovering a Class E result after the building layout is fixed is a costly problem. Discovering it during the concept phase gives you real design freedom.
The Actiflow Wind Assessment Tool is specifically built to support this — integrating wind assessments into early design phases so that results inform decisions rather than just document them.
How Actiflow helps with pedestrian wind comfort assessments
We carry out pedestrian wind comfort assessments for architects, developers, structural engineers, and municipalities — using both CFD simulations and wind tunnel testing, depending on what the project requires. With over 21 years of experience in wind engineering, we know what municipalities in the Netherlands and Belgium expect from a NEN 8100 report, and we apply the Lawson criteria for international projects in the UK, Gibraltar, and beyond.
Here is what working with us looks like in practice:
- We advise you on which study you need — NEN 8100 or Lawson, wind comfort or wind loading, CFD or wind tunnel — before you commit to anything
- We produce colour-coded comfort maps and graphics that you can share directly with clients, planners, or permit authorities without needing to translate the technical content
- We work at any scale — from a single high-rise to city-wide area studies like the one we carried out for the city of Rotterdam
- We are fast and flexible — for regular clients, we set everything else aside and start the next day if needed, and our internal automation continues to reduce delivery times
- We flag wind issues early and give you concrete design guidance, not just a report that tells you something is wrong
Curious how we can help with your wind comfort assessment? Contact us — we are happy to discuss your project and help you find the right approach. You can also find out more about us and the work we do.
