A wind assessment should ideally be commissioned at the start of the schematic design phase, before the building layout and massing are fixed. At that stage, findings can still directly influence design decisions without causing costly revisions. The later you commission a wind study, the more limited your options become if problems are found. The sections below answer the most common questions project managers and structural engineers ask about timing, legal requirements, methodology, and what to do when results flag a hazard.
At what stage of a building project should a wind study be commissioned?
Commission a wind study during the schematic design phase, as early as possible after the initial massing concept is defined. This is the point where the building’s height, footprint, and orientation are taking shape but have not yet been locked in. Acting at this stage means that wind findings can still steer design decisions rather than force expensive revisions later.
If you wait until the permit application stage, you are essentially using the wind study as a compliance checkbox rather than a design tool. That works if the results come back clean, but if the study flags a wind hazard, you may be looking at significant changes to facade geometry, building orientation, or ground-level layout at a point when those changes are expensive and disruptive.
For large area developments or masterplans, an early-stage wind assessment is even more valuable. At the urban planning level, decisions about street orientation, building clustering, and open space placement have a direct effect on pedestrian wind conditions. Catching problems at that scale is far easier than trying to fix them building by building later in the process.
A practical rule of thumb: if your project involves a building significantly taller than its surroundings, or an open public space at the base of a high-rise, commission the wind study before the design is presented to the municipality. This gives you time to respond to findings and strengthens your permit submission.
Is a wind assessment legally required for your project?
In the Netherlands, a wind assessment is legally required for permit applications where wind nuisance or wind hazard is a realistic concern, particularly for high-rise buildings and area developments. The applicable standard is NEN 8100, which defines wind comfort classes and sets thresholds for wind nuisance (exceedance of 5 m/s at eye height) and wind hazard (exceedance of 15 m/s). For projects in the UK and other international contexts, the Lawson criteria are the standard reference.
Whether a municipality will formally require a wind study depends on the project type and local policy. In practice, most municipalities request one for buildings above roughly six to eight storeys, or for developments that significantly alter the existing urban fabric. Some municipalities have their own additional requirements on top of the national standard, which is why familiarity with local policy matters as much as technical expertise.
Even when a wind study is not formally required, commissioning one voluntarily is often a sound decision. A report that demonstrates acceptable wind conditions strengthens a permit application and reduces the risk of objections from planners or local residents. Discovering a wind problem during the permit process, rather than before it, is a situation worth avoiding.
What is the difference between a wind comfort study and a wind loading assessment?
A wind comfort study assesses the wind conditions that pedestrians experience at ground level around a building. A wind loading assessment calculates the wind forces acting on the building’s structure and facade. These are two distinct studies with different inputs, methods, and outputs, and they serve different people on the project team.
Wind comfort studies produce results in terms of wind speed exceedance probabilities, classified according to NEN 8100 or the Lawson criteria. The output is typically a set of colour-coded maps showing which areas around a building are comfortable for sitting, strolling, or walking through, and which areas present a hazard. These maps are directly useful for architects, urban designers, and permit authorities.
Wind loading assessments, by contrast, produce pressure coefficients and force data that structural engineers and facade contractors use to size cladding systems, connections, and load-bearing elements. The relevant standard here is NEN-EN 1991-1-4 (Eurocode 1). This type of study is not about pedestrian comfort but about structural integrity and the safe design of the building envelope.
On a typical high-rise project, you may need both. The comfort study informs the design and supports the permit application. The loading study informs the structural and facade engineering. They can be run in parallel, and using the same consultant for both can save time on model setup and data sharing.
How does CFD simulation differ from a physical wind tunnel test?
CFD (Computational Fluid Dynamics) simulation and physical wind tunnel testing both produce reliable wind data, but they suit different project types and scales. CFD uses computer simulation to model airflow around a building or across an urban area. A wind tunnel test uses a physical scale model placed in a controlled airflow. For large-scale urban studies, CFD is the practical choice; for individual buildings or smaller masterplans, both methods are viable.
In a CFD simulation, a 3D model of the building and its surroundings is built from geodata, and the airspace around it is divided into millions of computational cells. The software then solves the airflow equations for each cell across multiple wind directions. The Rotterdam city-wide wind study carried out by Actiflow used a mesh of more than 583 million cells and required over 1,500 CPU cores to run, which illustrates the computational scale involved in large urban assessments.
Wind tunnel testing involves constructing a physical scale model and exposing it to controlled airflow in a laboratory setting. This method has a long track record and is well-accepted by permit authorities. Its limitation is physical scale: modelling an entire district or city in a wind tunnel is not practical, and the cost of building and modifying physical models adds up quickly during iterative design phases.
For most building projects in 2026, CFD is the dominant method because it is faster to iterate, easier to visualise, and scales to any project size. The output, colour-coded wind maps and graphics, can be shared directly with clients, planners, and permit authorities without requiring technical interpretation. You can learn more about how we apply both methods on our wind engineering page.
What inputs does a consultant need to start a wind assessment?
To start a wind assessment, a consultant needs a 3D model or detailed drawings of the proposed building, information about the surrounding buildings and urban context, and the intended uses of the ground-level spaces around the building. The more complete this information is at the start, the faster the study can proceed.
In practice, the minimum inputs needed to begin are:
- Building geometry: A 3D model, BIM file, or detailed architectural drawings showing the massing, height, and footprint of the proposed building
- Site context: Information about surrounding buildings within at least 500 metres, including heights and approximate footprints
- Intended ground-level uses: Which areas are entrances, public spaces, terraces, or pedestrian routes, since this determines which comfort class applies
- Project location: To determine the applicable wind climate data and the relevant standard (NEN 8100 for the Netherlands, Lawson for international projects)
- Permit requirements: Any specific requirements from the municipality or client regarding the scope or format of the report
For projects in the Netherlands, the wind climate data comes from KNMI meteorological datasets referenced in NPR 6097, which is the dataset required for permit procedures under NEN 8100. For international projects, equivalent national datasets apply. Geodata for the surrounding context can often be sourced directly from public databases such as 3DBAG and AHN, which reduces the burden on the project team.
If you are at an early design stage and the building geometry is not yet finalised, that is not a reason to delay. A preliminary assessment based on the current massing concept can already identify risk areas and inform design decisions before the geometry is locked in. Our fluid dynamics consultancy team regularly works from early-stage sketches and iterates as the design develops.
What happens if wind assessment results show a hazard?
If a wind assessment identifies a wind hazard, the next step is to explore mitigation measures. Most wind problems can be addressed through design adjustments, and the earlier they are identified, the more options are available. A hazard result does not automatically mean a project fails; it means the design needs to respond to the wind conditions at that location.
Mitigation measures follow a hierarchy from most to least effective:
- Urban planning level: Adjusting street orientation, building clustering, or the spacing between towers. The Manhattan effect, where towers cluster to protect each other, is a well-established design strategy. A useful rule of thumb is to keep height differences between adjacent buildings within 30%.
- Building volume and orientation: Rotating the building to reduce the broadside presented to the prevailing wind, adding setbacks at lower floors (a minimum of 5 metres depth for a building of around 100 metres height), or tapering the facade profile.
- Architectural elements: Canopies, covered walkways, and aerodynamically shaped facades can redirect wind away from pedestrian areas. These are less effective than volume changes but useful when the overall massing is fixed.
- Ground-level landscape measures: Trees, hedges, and screens can improve pedestrian comfort in specific locations. These work best as a complement to building-level measures, not as a substitute for them. Deciduous trees lose their leaves in winter, which is when wind speeds are highest, so they provide less protection when it matters most.
Under NEN 8100, wind hazard is defined as an exceedance probability of 15 m/s at eye height above 0.30%, and this threshold is considered unacceptable. Locations above this threshold require intervention. Locations between 0.05% and 0.30% may be acceptable depending on the context and use of the space.
The important principle is that wind problems are much easier to solve at the urban planning or massing stage than at the detailed design stage. If a wind study flags a hazard after the building design is largely fixed, the available mitigations are more limited and typically more expensive to implement. This is the strongest argument for commissioning a wind assessment early.
How Actiflow helps with wind assessments
We have been carrying out wind assessments since 2005, working with architects, developers, structural engineers, and municipalities across the Netherlands, Belgium, the UK, and internationally. Our team understands both the technical side and the regulatory requirements, including the specific policies of individual municipalities, which means we can advise you on what is needed for your project before the study even starts.
- Wind comfort assessments using CFD simulation and wind tunnel testing, classified according to NEN 8100 (Netherlands) or the Lawson criteria (international)
- Wind loading studies for facade contractors and structural engineers
- Large-scale area and city-wide wind studies, including the comprehensive wind study commissioned by the city of Rotterdam
- Clear, colour-coded output maps that can be submitted directly to municipalities or shared with clients without technical translation
- Fast turnaround, with flexibility to prioritise urgent projects and start the next day for regular clients
- A single point of contact from intake to final report, with experience across projects of all scales
Curious how we can help with your wind assessment? Contact us and we will be happy to discuss your project and help you find the right approach. You can also find out more about us and our background in fluid dynamics engineering.
