Living walls are springing up in our cities, often on luxury hotels, office blocks, and major stores.
Also called green walls, their benefits include increasing wildlife biodiversity and improving air quality.
The UK Green Building Council has called for all new buildings and infrastructure to include nature-based solutions by 2030 as our cities heat up, and living wall systems can be a part of that vision.
However, critics accuse them of being `marketing greenwash’ due to the carbon emissions created in their construction, usually from steel and concrete, which their benefits can’t neutralise.
Let’s take a closer look at living walls.
What is a living wall?
Following the development of green roofs in the 2000s, living walls first appeared in Germany in the 2010s and spread across Europe. Living wall systems enable walls to be planted vertically with shrubs, flowers, and grasses in soil or using a hydroponic system to keep them watered: they also need materials and manpower to maintain them. While they’re praised for increasing biodiversity, the environmental footprint of a living wall depends on factors including its installation in terms of carbon emissions, the amount of water required, and the drip irrigation system used.
A living wall can contain foliage plants, climbing plants, herbaceous perennials and flowering plants, or a mixture of all these. It’s important to get the plant selection right to suit the chosen living wall system, as this is the best way to ensure healthy plants.
The benefits of a living wall
As well as helping biodiversity, a living wall can:
- Absorb heat and cool the air around it, lowering temperatures in cities. A green wall can be up to 32 degrees cooler than a conventional wall and reduce air temperature around it by up to 4%.
- Help ecosystems to be resilient to climate change. Plants absorb carbon; a tree absorbs around 5.5kg of carbon dioxide per year and 1m2 of a green wall can absorb up to 2kg per year.
- Help reduce air pollution by removing toxins from the air such as nitrogen dioxide.
- Reduce noise inside a building.
- Help reduce flooding by absorbing rainwater.
- Add greenery via a vertical garden rather than using up valuable horizontal building space in a city for landscaping.
- Add character and be aesthetically pleasing. By bringing the natural world into a city landscape, a green wall provides enriching green space, giving a sense of well-being which can benefit our mental health.
- Increase footfall by making shopping areas more appealing.
- Give companies installing them the opportunity to boost their green credentials to customers.
Criticism of living wall systems
- To keep them in good condition they can need high maintenance, making them less sustainable than a green roof.
- They are accused of being `more style than substance’ and not really delivering benefits when their construction costs and carbon emissions are accurately taken into account, leading to claims of `marketing greenwash’.
- A living wall is very manicured – a scruffy green wall maintained with minimal effort will attract more wildlife than one that’s beautifully maintained.
- The fact that they turn brown and die back in winter is an aesthetic problem for some people who find their appearance untidy, but they do provide habitat at all times of the year.
Examples of living walls
Specialist firm Scotscape has been installing living walls since 2008 with the aim of creating biodiversity corridors to connect inner cities and the countryside, and states that introducing sustainable planting in the right places creates ecosystems that encourage biodiversity. Their green walls use smart technology and are flexible and lightweight to support mature plants and trees which can trap increased amounts of particulates from the air. They use native plant species, those on the Royal Horticultural Society pollinator list, and insect and bird boxes.
Scotscape designed and installed two green walls for Plymouth University, the biggest of which wraps around the Sustainability Hub building entrance. Research by the university in 2021 found that a living wall can reduce heat loss from buildings by over 30%, which they believe could help the UK achieve its net zero commitments.
Another company has designed a model to minimise its environmental footprint, costs, and carbon emissions. Green walls created by Vertical Meadow are designed for construction site hoardings, scaffolding, and building facades. They aim to be community assets, offering visual screening and reducing dust and noise while promoting the client’s brand.
This temporary `wrapping’ model sees plants grown from seed in situ, making the system lighter, thinner, more cost-effective, and easier to maintain. The wrapping is delivered to the site, connected to an irrigation system, Wi-Fi, and power, then switched on to start the germination process. Plant health is then monitored by maintenance apps and inspections; it needs nutrient replenishment and one or two monthly cuts. This system is approved by the Wildlife Trusts and Buglife (the Invertebrate Conservation Trust).
Problems with the take-up of green walls
One issue is their perceived lack of return on investment. However, as a report by the UK Green Building Council (UKGBC) indicates, green infrastructure such as a living wall can generate many benefits for businesses as well as the environment and society. Along with helping mitigate the impact of climate change, flooding, and overheating in buildings, in some cases they can be helpful in achieving planning permission where a local authority has a green agenda.
Kai Liebetanz, Senior Sustainability Adviser at the UKGBC said that green walls are valuable, providing that there are sufficient maintenance processes in place, clearly distributed responsibilities, sustainable costs and accountabilities.
Walls should ideally be optimised for biodiversity, and preferably utilising native vegetation. Green/living walls can contribute to biodiversity, improved air quality, and a range of other benefits which are clarified in our report, the Value of Urban Nature Based Solutions. The main drawbacks relate to maintenance, which can be costly or complex and so must be factored into any proposal.
We expect them to continue to be implemented across the built environment particularly in new developments, as they can be helpful in meeting new regulations for Biodiversity Net Gain. We also hope for wider uptake in retrofit projects, to share the benefits more broadly.
The UKGBC’s 2020 report, Making the case for green infrastructure, included an analysis of two sites where living walls had been installed. The first, in London, called the Wild West End project, has been undertaken by the area’s biggest property owners working together to improve green infrastructure and inspire others to do the same. They have a shared vision to enhance biodiversity and ecological connectivity, reduce air pollution, and add to the well-being of residents, workers, and visitors.
The project is ongoing, and its key aim is to create green stepping stones between areas of existing parkland, through the provision of green roofs, living walls, planters, street trees, and flower boxes, providing welcoming spaces for species once common in London such as the black redstart and the house sparrow.
Developers include Grosvenor and The Crown Estate, and key contributors include technical partner Arup, Greater London Authority, London Wildlife Trust, and Westminster City Council. Regular meetings are held to assess the scheme’s net gain. One finding is that while green infrastructure can be viewed as `nice to have’, businesses feel it costs money while not creating value: the project aims to demonstrate that the value may not be in monetary form but in environmental, social, and health benefits.
A second case study in the report focused on the 167m2 living wall designed by ANS Group Global as part of a refurbishment of the Marks & Spencer store in Newcastle. Its aims were to help improve the store’s sustainability performance, demonstrate its green credentials to customers, look striking and encourage biodiversity. The living wall plants include 16,000 native species including thyme, wild strawberries, and cranesbill. The system is compost-based and harvests rainwater for the plants, while the plant selection chimed with the M&S brand. Its green infrastructure benefits include urban cooling, provision of bird and insect food and habitat, improving health and well-being while being a great addition to the high street.
The outlook for living walls
They look set to become more common in our towns and cities as installation frame design becomes more environmentally sustainable, overcoming `greenwashing’ criticism. Different systems have evolved to use rainwater, and manufacturers are adding native plant species and plants that provide nectar, along with specific habitat boxes and bird boxes to improve the biodiversity of their products.
However, the performance of a living wall depends on its design, location, surroundings, and the building it’s installed on. Their benefits in helping obtain planning permission may become more relevant as developers need to meet Biodiversity Net Gain targets coming into force later this year, requiring them to leave the natural environment in a measurably better condition than it was before their intervention.
It’s also likely that businesses will increasingly recognise the advantages of a living wall in terms of customers’ perception of their environmental credentials – so, expect to see them springing up in outdoor spaces near you soon!