Green Sky Thinking: TfL's Green Wall in Central London
Footprint climbs Biotecture’s green wall at Edgware Road Station
As part of Green Sky Thinking, Footprint attended a seminar hosted by Tim Wraight, operations manager at Biotecture. Over twenty professionals attended the event, which covered the construction process and watering system of the green wall.
Commissioned by Transport for London back in 2011, the 180m² south-facing wall of Edgware Road Station was clad to test its ability to remove pm10 pollutants from the air.
The substructure consists of vertical timber cladding rails at 1200mm centres, attached to the wall via stainless steel angle brackets fixed into the existing brickwork. Ecosheet backing board is then fixed to the cladding rails. Plants were installed at the very end stage to avoid all potentially hazardous works. The plants were pre-grown vertically in a modular hydroponic system with nutrients provided through irrigation channels enabling long-term, stable conditions for them to flourish, while also reducing pest risks.
Main characteristics of the system:
- Independent units of 600mm x 445mm
- Units irrigated by 4 drippers at 150mm spacing
- Construction cost: £600 - £800 per m2
- Hydroponic system
- Integrated design enables moisture control to reduce water consumption
- Includes sun resistant plants such as lavender, geranium and Stachys
- Modular system which allows quick construction
- The wall panels comprise horticultural rockwool manufactured by Grodan within a regenerated plastic case
- Each panel has capillary breaks for water descent control
Plants are irrigated with a remote control system at an average of 1 litre per m2 per day. Comparitive traditional planting bed systems require 3-4 litres per m2 per day.
Tim explains ‘there are three irrigation zones in Edgware Road with an annual average operation of 4 minutes per day per zone with annual pump running costs of £125.’
During the seminar Tim highlighted that these systems need to be carefully thought out from the beginning, in order to plan in maintenance and reduce costs. This particular wall has a warranty of 10 years and is controlled by remote sensing. Elevated work platforms enable easy access to the plants keeping the client’s maintenance costs down.
Funded by the government’s Clean Air Fund, Imperial College London is monitoring the wall to assess the selected plants for their ability to release oxygen and remove pollutants from the air. At one of London’s busiest junctions, the green wall will boost biodiversity along Edgware Road while reducing noise pollution. It is also predicted that evapotranspiration by the plants will reduce the temperature of the air, mitigating the urban heat island effect.