Wind Microclimate Assessment
Tall buildings and large-scale developments can significantly alter wind patterns at ground level, creating uncomfortable or even dangerous conditions for pedestrians, cyclists, and people using outdoor spaces. A Wind Microclimate Assessment evaluates these effects and ensures that the development creates an acceptable wind environment in and around the site. As cities grow denser and buildings grow taller, wind microclimate has become an increasingly important consideration in the planning process.
Typical Cost
£300 – £5,000+
Turnaround
1 – 6 weeks
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What is a Wind Microclimate Assessment?
A Wind Microclimate Assessment is a specialist study that predicts the wind conditions at pedestrian level in and around a proposed development. It evaluates how the building massing, orientation, and surrounding context will affect wind speeds and gustiness at ground level, and compares the predicted conditions against the Lawson Comfort and Safety Criteria — the industry-standard benchmarks for wind suitability. The assessment identifies areas where wind conditions may be uncomfortable for the intended use (such as sitting, standing, or walking) or where safety thresholds could be exceeded.
When is a Wind Microclimate Assessment required?
A Wind Microclimate Assessment is typically required for developments involving buildings of 10 or more storeys, tall buildings that significantly exceed the height of their surroundings, developments in exposed locations such as waterfronts or hilltops, schemes with large open spaces or podium-level amenity areas, mixed-use developments with ground-floor retail or restaurant terraces, and any development where the local planning authority considers that wind effects could be a material consideration. In London, the requirement is common for tall building applications and is addressed in several borough local plans and the London Plan itself.
What does a Wind Microclimate Assessment include?
A comprehensive Wind Microclimate Assessment includes a description of the site location, surrounding building context, and prevailing wind conditions, identification of the assessment methodology — either Computational Fluid Dynamics (CFD) modelling or wind tunnel testing, analysis of wind conditions at key pedestrian locations including building entrances, walkways, bus stops, seating areas, and amenity spaces, comparison of predicted wind speeds against the Lawson Comfort Criteria for the intended use of each location, assessment of the worst-case scenario for safety, identifying any locations where wind speeds could pose a danger to vulnerable pedestrians, analysis of the development's impact on wind conditions in the surrounding area, and recommendations for mitigation measures such as canopies, screens, planting, and building design modifications where adverse conditions are identified.
How much does a Wind Microclimate Assessment cost?
The cost of a Wind Microclimate Assessment depends primarily on whether CFD modelling or wind tunnel testing is used. A CFD-based assessment for a standard tall building development typically costs between £5,000 and £12,000. Wind tunnel testing, which involves constructing a physical scale model and testing it in a boundary layer wind tunnel, is more expensive — typically £15,000 to £40,000 depending on the size and complexity of the model. Very large developments with multiple tall buildings and extensive public realm may require assessments costing £40,000 to £80,000.
Who can prepare a Wind Microclimate Assessment?
Wind Microclimate Assessments are carried out by specialist wind engineering consultants or environmental physics consultancies with expertise in pedestrian-level wind studies. Practitioners should have advanced qualifications in fluid dynamics, meteorology, or environmental engineering, and experience with CFD software such as ANSYS Fluent, OpenFOAM, or StarCCM+, or with boundary layer wind tunnel facilities. There are relatively few specialist wind consultancies in the UK, and the field requires highly specialised knowledge.
How long does a Wind Microclimate Assessment take?
A CFD-based Wind Microclimate Assessment typically takes 4 to 8 weeks to prepare, including model set-up, simulation runs, post-processing, and report writing. Wind tunnel testing has a longer lead time — usually 8 to 14 weeks — due to the time needed to construct the physical scale model, book wind tunnel time, and analyse the results. If the initial assessment identifies adverse conditions requiring design changes, additional iterations of the modelling and re-assessment add further time.
Frequently Asked Questions
What are the Lawson Comfort Criteria?
The Lawson Comfort Criteria, developed by Tom Lawson, classify wind conditions at pedestrian level according to their suitability for different activities. The categories range from 'sitting' (the calmest, suitable for outdoor dining and prolonged rest) through 'standing' (suitable for bus stops and window shopping) and 'walking' (comfortable for pedestrian movement) to 'uncomfortable' (unsuitable for regular pedestrian use). A safety threshold identifies conditions where wind gusts could cause people to lose balance.
What is the difference between CFD and wind tunnel testing?
CFD (Computational Fluid Dynamics) uses computer simulations to model airflow around buildings, while wind tunnel testing uses a physical scale model of the development and its surroundings placed in a specialised wind tunnel. Wind tunnel testing is generally considered the gold standard for accuracy, particularly for complex sites with multiple tall buildings. CFD is faster and less expensive but requires careful validation. Some planning authorities and tall building review panels have preferences for one method over the other.
Do all tall buildings need a wind assessment?
Not necessarily, but most tall buildings will require one. The need depends on the height of the building relative to its surroundings, the exposure of the site, and the sensitivity of the ground-level uses. A 10-storey building in a city centre surrounded by buildings of similar height may have minimal wind impact, while a 6-storey building on an exposed waterfront site could create significant problems. The local planning authority will advise whether a wind assessment is needed.
What wind mitigation measures are commonly used?
Common mitigation measures include canopies and covered walkways at building entrances, solid or perforated wind screens at exposed corners, landscaping with trees and hedges to break up wind flow, recessing ground-floor entrances, stepping back upper storeys, introducing podium levels to deflect wind, and rounding building corners to reduce the venturi effect. The most effective approach integrates wind considerations into the building design from the outset rather than adding mitigation retrospectively.
What is the venturi effect?
The venturi effect occurs when wind is accelerated as it is funnelled through a narrow gap between two buildings or between a building and a barrier. The constriction forces the same volume of air through a smaller space, increasing its speed. In urban developments, this can create uncomfortably windy conditions at ground level between closely spaced buildings. The wind assessment should identify any locations where the venturi effect could occur and recommend design changes to alleviate it.
Can a wind assessment influence building design?
Absolutely, and ideally it should. Early-stage wind assessments can inform decisions about building orientation, massing, facade articulation, and the location of entrances and amenity spaces. Design changes at concept stage — such as rounding corners, stepping back upper levels, or adjusting gaps between buildings — can be far more effective and less costly than adding mitigation measures to a completed design. Engaging the wind consultant at RIBA Stage 2 or earlier is strongly recommended.
How are existing wind conditions accounted for?
The assessment models wind conditions in the 'existing' scenario (the current site with existing buildings) and the 'proposed' scenario (the site with the development in place). Comparing the two scenarios reveals the specific impact of the development on the local wind environment. Meteorological data from the nearest weather station provides the statistical basis for the prevailing wind speeds and directions used in the analysis.
What happens if safety criteria are exceeded?
If the assessment identifies locations where wind speeds exceed the safety threshold — meaning there is a risk that strong gusts could cause pedestrians to stumble or lose balance — the design must be modified to eliminate these conditions. Safety exceedances are treated very seriously by planning authorities, and unresolved safety issues will almost certainly result in a recommendation for refusal. Mitigation through screens, canopies, or design modifications must be demonstrated to be effective through re-assessment.
Does the assessment consider cumulative effects?
Yes. The wind assessment should consider the cumulative effect of the proposed development in combination with other consented or planned developments in the surrounding area. This is important because multiple tall buildings can interact to create wind effects that would not occur from any single building alone. The cumulative scenario typically includes schemes with planning consent that are not yet built, using massing information from those applications.
Are roof terraces and balconies assessed?
Yes. Elevated outdoor spaces such as roof terraces, sky gardens, and balconies are exposed to higher wind speeds than ground-level areas and should be included in the assessment. The Lawson criteria for 'sitting' are applied to seating areas on terraces, and the assessment should demonstrate that conditions will be comfortable for the intended use. Balcony-level winds are typically stronger than ground-level conditions, and mitigation such as glass balustrades and overhead screens may be needed.