WIND IMPACT: UNDERSTANDING MICROCLIMATES AND PEDESTRIAN IMPACT

In this post, we explore a force of nature that profoundly shapes our urban environment: the wind. It is essential to understand the technical considerations behind the buildings that surround us, particularly as London’s skyline continues to rise.

Have you ever experienced a sudden, downward gust of wind while cycling that nearly forced you off your path? Or perhaps you have walked past a tall building where the wind became so turbulent that maintaining a straight line became a challenge? These phenomena are not mere weather accidents; they are the result of the microclimates created by the built environment.

The Phenomenon of "Down-draught"

When an architect plans a building that is significantly taller than its immediate context, that structure will have a measurable environmental impact on its surroundings. In simple terms, as wind moves across the city, it strikes the broad facade of a tall building. Unable to move through the structure, the air is "caught" and deflected downwards toward the ground at high velocity.

This is why certain routes in London, such as the area between the south of Blackfriars Bridge and Court Street, can become particularly challenging for cyclists and pedestrians during the winter and early spring.

Strategies for Mitigation

Just as one might add texture to a room to improve its acoustics, architects can manipulate the facade of a building to manage wind velocity. However, surface texture alone is often insufficient. To ensure pedestrian comfort and safety, we must often integrate additional architectural features, such as:

• Cantilevered Canopies: Positioned above the ground floor to deflect downward air currents away from the pavement.

• Strategic Tree Lines: Utilising soft landscaping to break the force of the wind at street level.

• Facade Geometry: Utilising "stepped" massing or porous elements to dissipate wind energy.

The Role of Wind Microclimate Assessments

When planning a tall building, a critical step in the design process is the Wind Microclimate Assessment. This is a highly technical exercise that often involves the following steps:

1. Physical Modelling: A precise scale model of the proposed building and its surrounding context is constructed.

2. Sensor Placement: Small perforations are made in key areas of the model to measure pressure and velocity.

3. Wind Tunnel Testing: The model is placed within a controlled wind tunnel. In some instances, smoke is used to visualise the airflow patterns and identify areas of high turbulence.

4. Computational Fluid Dynamics (CFD): Digital simulations are also used to predict how the wind will behave in various weather scenarios.

The resulting report provides indispensable data on wind speeds at ground level and offers recommendations for mitigation to ensure the safety of the public.

Engaging with Local Consultations

If there are proposals for tall buildings within your neighbourhood, it is common to be told during public consultations that such developments are permissible because other high-rise structures have already been approved nearby.

As an informed member of the community, you may wish to enquire about the Wind Microclimate Analysis and the specific mitigation measures the design team has integrated. High-quality architecture should not only look impressive on the skyline but must also contribute to a safe and comfortable environment at street level.

Architectural Expertise in Urban Contexts

At our studio, we believe that architecture must be sensitive to the invisible forces that dictate the quality of urban life. Understanding these technical complexities is fundamental to responsible design.

Have you noticed specific areas in London where wind turbulence makes walking or cycling difficult? We invite you to share your experiences below. If you are developing a project in a dense urban area and require advice on environmental impact, please reach out to our studio.