A bit of green :: Green Walls / Living Walls

Green Walls / Living Walls

A green wall at São Paulo.

A green wall is a wall partially or completely covered with vegetation. Green walls can either be free-standing or part of a building. There are two main categories of green walls: green façades and living walls. The vegetation for a green façade is attached on outside walls, but there is also the case of indoor living walls where the vegetation lies on interior walls. Green walls are also referred to as living walls, biowalls, or vertical gardens.

Green façades are made up of climbing plants either growing directly on a wall or, more recently, specially designed supporting structures. Vertical gardening isn’t a new idea; for aeons, people have been staking tomato plants, and espaliering trees. Actually, the espaliering technique was very popular in the Middle Ages! In all these techniques, the plant that grew up the side of the wall has always been rooted to the ground.

However, the green wall of the 20th century has absolutely no dependency on the ground. Living walls actually exploit the fact that plants do not really need soil to grow, as long as they have water and the minerals found in soil. Light and carbon dioxide, needed for the plant to conduct photosynthesis, should be plenty around in our urban environment. Without soil, the plant supporting system is very light; a vertical garden can be realised anywhere, as long as we provide it with these 4 things: water, minerals, light and carbon dioxide.

The new -and much safer for the building- vertical garden methods suggest a steel framework for structural integrity, a waterproof backing material to keep water off the walls and felt fabric for the plants to adhere and grow into. Patrick Blanc, a French Botanist, is the one who came up with the idea of this system, using the ability of plants to grow roots spreading on the surface rather than the depth of a material. Whenever roots are allowed to grow deep inside a wall, they can easily damage it and cause its destruction. This root-related damage can be prevented if the plants are regularly watered. This way roots are only spreading on the surface, leaving the inner wall unaffected.

The plant species selection is mainly set according to the prevailing climatic conditions. In general, plants with shallow roots are better, because they can stay easier on a vertical wall. All kind of flowers and plants can be planted on a vertical garden, including epiphytes, tropical plants, ferns or herbs. The plants used can be seeds, cuttings or already grown plants.

Vertical gardens require more maintenance than gardens in traditional horizontal plane. Fertilisation and watering (usually using nutrients enriched water) should be automated to insure the needed ingredients are evenly -and regularly- distributed. For indoor installations, artificial lighting is usually required.

Jean Nouvel’s Musée du quai Branly

A great indoor vertical garden example.

Les Halles, Avignon

Green walls are found most often in urban environments where the plants act as insulating material. A green wall can reduce energy consumption because the plants protect the building from the cold in the winter and act as a natural cooling system in the summer. The primary cause of heat build-up in cities is insulation, the absorption of solar radiation by roads and buildings in the city and the storage of this heat in the building material. Plant surfaces however, as a result of transpiration, do not rise more than 4–5 °C above the ambient and are sometimes cooler. In addition to leaves and their well-known air improving effect, the roots are acting a as a wide air-cleaning surface. Polluting particles (such as VOCs, mentioned before here) are taken in from the air and are slowly decomposed and mineralized on the felt material. Overall, green walls can be used for air cleaning, water reuse, diminishing energy costs or just for the sake of filling a wall with life.

However, big scale vertical gardening projects can be really expensive; the species and the demands of the plants as well as the automated systems used are greatly affecting the cost of the project. Living walls can be difficult to maintain, since they need constant care.

A saddening example of vertical garden gone wrong is the living wall of the Paradise Park Children’s Centre in London – a living wall that isn’t living anymore. DSDHA architects designed the building and its living wall, covered in geraniums and euphorbia, which was completed in 2005 and used recycled rainwater for irrigation. It was this irrigation system that seemed to break down, causing the plants to dry out. Apparently, the centre’s living wall cost 100,000£, which is now criticized as a waste of public money.