North Audley Street forms an important connection between Oxford Street and the heart of Mayfair. During the COVID-19 pandemic, Westminster City Council and Grosvenor Property UK commissioned a temporary public realm scheme to create a more welcoming, pedestrian-friendly environment that supported local businesses and outdoor hospitality. The success of the temporary installation led to a permanent transformation of the street, delivering enhanced public space, new tree planting and integrated sustainable drainage infrastructure.
The permanent scheme, designed by Publica and WSP and delivered by FM Conway, widened footways, improved pedestrian movement and introduced new planting to strengthen the connection between Grosvenor Square and Oxford Street. As part of the permanent works, two semi-mature American Sweetgum trees were planted to extend the existing tree avenue and provide long-term environmental benefits.
The project presented significant technical challenges. Shallow basement structures beneath the footway, limited pavement build-out width and a dense network of underground utilities severely restricted available rooting volume and excavation depth.
To overcome these constraints, WSP designed, with guidance from GreenBlue Urban, a compact SuDS tree pit solution using RootSpace 600 structural soil cells, creating a load-bearing rooting environment beneath the paved surface. The system provides sufficient uncompacted soil volume for healthy root development while maintaining the structural performance required within a busy city streetscape.
Each tree pit was equipped with RootRain ArborVent irrigation and aeration systems, together with trafficable aeration inlets integrated into the paving surface. This combination ensures effective delivery of water and oxygen directly into the root zone, supporting successful establishment and long-term tree health.
Rainwater from the road is directed into the tree pits through nearby drainage gullies. Before entering the system, sediment and debris are captured to help keep the drainage network functioning effectively and make future maintenance easier. This helps ensure clean water reaches the trees while protecting the long-term performance of the system.
The SuDS tree pits were designed to capture and manage runoff directly from the surrounding streetscape. Water is stored and filtered within the engineered soil profile before being discharged to the existing combined sewer network.
By combining tree planting with sustainable drainage, the scheme delivers multiple benefits within a constrained urban footprint. The trees contribute shade, biodiversity and improved air quality, while the SuDS infrastructure helps increase capacity within the drainage network and supports resilient surface water management.
The project represents a pioneering approach within Westminster, demonstrating how green infrastructure and SuDS can be successfully integrated into high-value urban environments where available space is limited.
Project Managers:
Thompson Cole and WSP
Installation Photographs Credit: Publica
