Whitehall Sidings is becoming a major residential development on the edge of Holbeck, Leeds, comprising a 27-storey tower alongside a lower warehouse block. Leeds is one of the windier major cities in the UK, and Whitehall Sidings occupies a particularly exposed site. With considerable height, any proposed tower would intercept winds well above street level, making wind an important design consideration from the outset.
Shaping the massing around the wind
Before detailed modelling began, ArcAero mapped the dominant wind sector against the constraints of the tapering site. Existing buildings offered a small amount of shelter from winds towards the west-northwest, but most of the site remained exposed to the more important west-southwesterly and south-westerly winds. Our advice was therefore to use the position and orientation of the buildings as the first line of defence. Taller, more elongated elements could be concentrated towards the northwestern part of the site and arranged to perform better against the least-sheltered wind directions. Their positioning could then provide some shelter for development further along the plot, allowing the remaining block to be less elongated and oriented more directly towards due-westerly winds.
Testing the emerging design
The proposals evolved considerably from these early multi-block studies. The same broad principle remained: the high-rise element was positioned towards the northwestern end of the site, well oriented for the most problematic winds, with the lower block extending along the plot. Initial configurations still produced safety exceedances at ground level. Downdrafts from the taller elements combined with channelling between buildings, creating localised areas for further attention. The interactions were complex. Improving one location could shift or intensify the flow elsewhere, so the work moved beyond broad massing advice into detailed diagnosis and option testing. Detailed CFD allowed the critical wind directions to be isolated and the combined lateral and downward movement of air around the development to be traced.
Turning complex airflow into practical advice
That detailed modelling generated a substantial amount of technical information. The next task was to turn it into advice, in the form of a simple sketch, that designers could easily use. The principal wind directions and flow mechanisms were summarised, distinguishing areas dominated by lateral flow from those requiring protection against a stronger vertical component. The sketch identified where horizontal cover would be useful, where vertical screening was needed, where boundary treatment could help and where a bespoke combination of measures was required. That interpretation was important. A canopy can intercept descending wind but may do relatively little against fast-moving lateral flow. A vertical screen can break up horizontal movement but may redirect wind around its ends. The eventual strategy therefore matched different forms of protection to different airflow mechanisms: overhead cover where wind was being drawn down from the warehouse block towards ground level, and gantries and porous screens where strong swirling and lateral flows needed to be disrupted.
Verifying the developed design
CFD provided the speed and flexibility needed to explore the design, compare alternatives and identify the critical locations. The developed scheme was then tested physically in the Imperial College wind tunnel. In most areas, the two approaches agreed well, giving confidence in the overall picture and allowing the wind tunnel to verify the preferred design rather than begin the investigation from scratch.
What the CFD missed
At the junction between the tower and warehouse block, the CFD predicted comparatively calm conditions. The wind-tunnel measurements instead recorded a more active recirculation region. Traditional flow visualisation was used to investigate further, with wool tufts showing the strong swirling movement of air between the two buildings. The same airflow then continued laterally at ground level further along Springwell Road. These findings helped to define where the gantries and porous screens were required to interrupt and diffuse these flows. This shows why it can be important to use both CFD and wind-tunnel modelling, particularly for taller schemes in windier cities.
From wind mitigation to place-making
The final strategy used the canopy structure to combat wind being drawn down from the warehouse block towards ground level. Gantries and porous screens helped disrupt the strong swirling flow between the tower and warehouse block, as well as the wind moving laterally further along Springwell Road. Operable gates and locally protected roof-terrace seating completed the strategy, making sure of acceptable conditions without reliance on soft landscaping. Planting could instead contribute to the character and enjoyment of the spaces without carrying responsibility for safety. The railway infrastructure surrounding the site provided a natural design language for these measures. The gantries and screens became part of the identity of Sidings Gardens, helping to define its edge, preserve public access and create useful, sheltered space. With the final measures in place, safety criteria were met throughout the study area. Entrances and pedestrian routes were suitable for their intended uses, while the ground-level gardens and roof terrace offered a mixture of conditions appropriate for play, movement, standing and sitting. Whitehall Sidings shows what wind engineering can contribute when it is treated as part of the design process: not simply a result, but a clearer understanding of the problem and a practical route towards a better place.
