Urban greening contributes a lot of benefits to the fabric and quality of life in an city environment, and the vertical plane is often the most readily available and underutilised space. Trees are fantastic and as a designer and consulting arborist, I will extol their virtues all day long, but viable root volume is often the limiting factor in their success. Living walls are a way to introduce large volumes of green biomass into a very small footprint, or no footprint at all.
For those that don’t know, I have instigated green walling in the UK and the UAE via two companies: originally, I conceived of and co-founded Biotecture Ltd in 2007 and later ran a smaller company, Vertology Ltd, up until Covid. I have designed and patented hydroponic systems and used them in climates as diverse as the UK, UAE, USA, Norway, Europe and Iceland. I still consult on these aspects of projects, often designing bespoke solutions to meet a specific situation.
I have always promoted the environmental benefits of vertical greening and not just aesthetics, which is the prevalent motivation for inclusion on projects. A small, dynamic area of wall will look good and be great for human biophilic interaction, but will miss out on the benefits of larger walls, which can be broken down into a number of distinct areas: client-user, building environmental, local microclimate and wider environmental. The list below in not exhaustive nor are they automatic benefits; some must be intentionally designed in and some may be considered contentious:
| Client-User | Building Environment | Local Microclimate | Wider Environment |
| Cooler environment | Heat insulation | Increased local habitat | Reduced urban heat island (UHI) effects |
| Biophilic connection | Reduced HVAC costs | Insect and bird food source | Wildlife corridors |
| Noise suppression | Noise suppression | Nesting for birds | Quieter streets |
| Air quality | Air quality | Bat habitats | pm10 particulate, NOX, VOC removal |
| Aesthetics/ambiance | Reduced absenteeism | Evapotranspiration | Increase of small hydrological cycle |
| Reduced building energy costs | Grey water reuse | Reduced water inflow and outflow | Reduced strain on national resources |
| Reduced water inputs | Harvested rainwater | Reduced local floods | Stormwater mitigation |
| Reduced wind speeds | Reduced heat loss | Sheltered habitats | Reduced wind canyons |
Systems of vertical greening that act as a comprehensive and integrated part of a building and its environmental functions, I call the ‘building biomembrane’, though this idea is far from universally known and needs comprehensive study and development. It is in areas like this, plus urban ecology, climate mitigation and ecosystem services where the landscape industry is lagging behind and missing out on a truly transformative role that is of value to the whole of society.
Vertical greening is not just living wall systems, there are many other ways of using plants on a building. the most obvious, and oldest, is the use of climbing plants. These have many advantages, the use is traditional and known, though needs some adaption to modern needs. Climbers are cheap to install, but have an increasing maintenance cost over time. The picture below shows what happens if maintenance is neglected or insufficient – established climber put on a lot of annual growth!
A more modern approach is to use climbers on frames or tensioned stainless steel cable/net supports. These (can) hold the climbers off of the building fabric, creating shade gaps with cooler temperatures. Where winter solar gain is a benefit, deciduous climbers are used, rather than evergreen, to allow winter sun to strike the building fabric. The project below (not by ML) shows an enclosed spec in a multi-story building with vertical climbers. Such systems are a possible retrofit option.
Indoor walls function well anywhere and in any climate, I have designed them from Iceland to Dubai and they use the same or similar plants, most of a sub-tropical nature (houseplants). They can also be designed to transition from inside to out, with a number of common species that will do well in both environments. There is one I designed in Trondheim, Norway that does this, with the exterior part being the most Northerly outdoor wall, to my knowledge. The benefits I have listed in the table, with biophilia topping the chart. Indoor walls will fail if not given the correct supplemental full-spectrum light.
I have been working with exterior living walls in the UAE for the the past 15 years, where with various business partners, we set up trials to test the suitability of plants. The palette of plants we arrived at is now in general use in the region. There are of course, challenges of extreme heat which can be unforgiving and many systems have been tried and failed. Unfortunately, the market is awash (there, and in the rest of the world) with systems that will not sustain plants in long-term health, nor in the harsh conditions. I believe the best way forward in arid climates is a hybrid of building shading structure and plant systems. I await the project to test this out!
It is not just residential or ‘high-end’ buildings that benefit from vertical greening, many utility buildings do also; car parks and data centres, power generation and temporary building hoarding are all prime areas to offer up greening to hide less attractive buildings, or provide some much needed greening.
The energy and water use on modern systems is pretty low. Irrigation pumps might operate for just a few minutes per day and use just 1-2 litres water per square meter. Even in the UAE, we we using about 5L/m2/day whereas horizontal planting uses about 16L/m2/day. For the 180m2 living wall at Edgeware Road in London, we calculated the electrical cost to be just a few £/year – less than a domestic kettle being used within the same building.
The weak point of any vertical greening is the long term commitment to maintenance. Installation is generally dealt with in a cap-ex budget, maintenance always gets cut, especially after initial contracts expire and work goes out to tender, or the building is sold. I’ve seen too many walls die because the client moves out and shuts the water off, or a new maintenance company doesn’t understand the system. Automation helps, but is only of use if the information is acted upon. Failures then, are human in origin, rather than systems failures, provided a reliable system has been chosen. Maybe we can develop automated maintenance systems to reduce the human maintenance input, though we should value and appreciate horticultural skill.
I fully believe that living walls and other elements of vertical greening have barely scratched the surface of what is possible. The future climatic needs may dictate that we stop designing ego-led buildings and start creating eco-led ones instead. There’s a lot to do, with fantastic potentials. If you have a project, do get in touch!
