According to the EPA, indoor air pollutants can be two to five times higher than outdoor air pollutants, making indoor air one of the top five environmental health risks. Poor indoor air quality (IAQ) is often due to poor ventilation and off-gassing of Volatile Organic Compounds (VOCs) from carpets, paints, upholstery, insulation and countless other common products.
Living walls—walls covered by plants which do not root in the ground, yet root in soil or mats suspended on the wall itself—can be used on any scale to improve indoor air quality. But it’s not just in the area of health that living walls provide benefit. They also save energy, reduce noise, protect a building, serve as an art and architectural medium and can be used to grow food or medicinal plants.
Living walls – background
There are two types of living walls: with a substrate and without. The most used substrate is sphagnum, commonly called peat moss. Living walls can be adapted to almost any size, View a photo gallery of living walls.
Living walls have been used for centuries in Europe; whether this was an intentional use of living walls or a natural process of local fauna overtaking an available medium probably depended on the cultural status of the occupants. Today, living walls are re-entering the spotlight as an environmentally friendly way to improve air quality, reduce energy costs and bring nature back into the human landscape.
Living walls provide both physical and psychological health benefits. The plants use CO2 and circulate the air in the room, removing VOCs from the ambient air. This reduces the negative health effects associated with VOCs and poor indoor air. Living walls therefore improve air quality through photosynthesizing; absorbing CO2 and emitting oxygen.
On a psychological level, plants can provide a calming effect as well as increase worker efficiency. Quantifying a psychological benefit from plants in a person’s space is somewhat difficult. However, qualitative reports of a general improvement in mood and calmness are common in measuring effects of plants on human psychology.
- Reduce the heat island effect – the sun’s energy that’s used to reflect and radiate heat from buildings gets absorbed by the plants.
- Increase the thermal performance of buildings (lowering energy consumption and costs) – shading from the plants on an exterior wall can decrease the temperature inside the building; lower temperatures indoors reduce the need for air conditioning.
- Lower greenhouse gas emissions – by reducing indoor cooling demands, less energy is used and less GHGs are emitted.
- Living walls absorb sound waves, reducing city noise.
Reduction of storm water runoff
- The soil from living walls absorbs rain, reducing runoff.
- Absorb acid rain, keeping it off the building.
- Protect against ultraviolet rays.
- Reduce temperature change, which reduces expansion and contraction of building materials.
- Living walls create habitat for microorganisms, insects and birds.
- Increase urban biodiversity and urban food production.
How do living walls improve indoor air quality?
Air quality is improved by a biological process called biofiltration. Air can be forced past the plants and the soil medium containing microbes, which remove VOCs, dust and dirt particles from the air. The pollutants from the air are absorbed into a liquid phase and consumed by the microbes. The microbes use the pollutants as an energy source and degrade them to carbon dioxide and water. The air is then pumped through the traditional HVAC system and is redistributed into the building. An estimated 65 to 90 percent of VOCs have been removed using biofiltration.
>How do living walls reduce cooling costs?
Shading from the plants on a sunlit wall reduces the amount of direct light hitting the structure. The energy absorbed by the plants is converted into sugars through photosynthesis instead of reflecting and radiating most of the energy (heat) striking the wall.
Indoor living walls can also reduce cooling/heating costs. Traditional HVAC systems must, by code, replace a certain amount of indoor air with fresh outdoor air every hour. While this is being accomplished, the outdoor air must be heated/cooled to the desired indoor temperature. With an indoor living wall system the same air is used over and over again. The air is filtered by the living wall and maintains its temperature, eliminating the need to heat and/or cool outdoor air.
How are living walls made?
Any plant requires a type of growing medium. Some plants require a lot of medium in order to flourish, other plants need very little. The first element to building a living wall is the physical structure of the wall. Plants need water and moist soil, two things not commonly found anywhere near drywall. Some method of retaining the drip from plants and soil is a good first step, for example, building little cubbies at slight upward angles.
Types of living walls
Living walls to choose from:
- Living walls can be made using a pallet
- The panel system is a pre-planted system that you can buy from a company such as panel specialists at ELT Living Wall Systems or VertiGarden. Once purchased you can either install the panels yourself or have an expert install them for you onto an existing wall, indoors or outdoors, along with an irrigation system.
- In Felt Systems plants are fitted into felt pockets of growing medium and then attached to a waterproofed backing which is then connected to the building behind. An example of a felt system is Patrick Blanc’s Vertical Garden and Bacsac Sac by Sac. Patrick’s system is composed of a metal frame, a thin PVC sheet, and a felt polyamode layer which is attached to the PVC.
- They can also be made DIY using a metal grating dressed with a jute mat and filled with potting soil, or using a EPDM plastic with felt matting, and sacs with potting soil and a irrigation system.
- Finally, a container/trellis system consists of vegetation that is grown in containers which climb onto trellises. Irrigation drip lines are put in place to control the watering and feeding of the plants.
If you consider living walls before the building’s construction occurs you can greatly reduce maintenance costs.
Once the initial panels are in place living walls require little maintenance. They are designed so their upkeep is about the same as a landscaped garden. Most important to the upkeep of living walls is their irrigation systems. Living walls are basically hydroponic systems where water and nutrients are fed to the wall through some means of mechanical irrigation. Some living wall systems are designed to collect rainwater and/or reuse gray water.
Some panels are designed to allow the water to flow from cell to cell within the panel and from panel to panel within the wall. The water flows internally within the panels. The water flows from the top grooves in each panel, through the subsequent grooves, until it reaches to bottom of the panel where it drips out from the drainage channels and into the panel below. Irrigation systems are designed with automatic timers for ease of use.
Types of plants to use
The plants you choose for your living wall can vary greatly, depending on the amount of sunlight available, the space available, the different places on your living wall (and different exposure to water), and whether your living wall is indoors or outdoors. There are many options to choose from. There are also many vegetables that have been grown successfully in living walls.
Some things to keep in mind
- Moisture must be controlled to avoid mould growth.
- Plants will attract insects.
- One must be careful to choose plants that won’t release excessive pollen.
- Plants must be maintained, including, trimming, watering, replanting and washing.