Retrofitting Green Buildings with Nature Based Climate Technology.

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The positive effects of an interior living wall on a person’s health and well-being have been widely documented. In recent times, however, studies are also turning their attention to the large-scale impact an exterior living wall can have on a building as a whole.

From moderating heat transfer and improving the performance of HVAC systems to boosting the efficiency of solar PV systems — the results may surprise you.

In this article, we examine each of the positive impacts an exterior living wall can have on an entire building, from the inside out.

A Reduction in the Need for Heating and Cooling Energy

Living walls are an innovative building envelope technology that attempts to solve a variety of challenges related to sustainability in our built environment.

Green living walls vary from other forms of botanical wall coverings in that they incorporate the planting substrate into the construction of the building’s surface. In doing so, studies have found that living wall facades have the potential to enhance the thermal performance of the building envelope.

Photography credit by Zauben

The building envelope (also referred to as an enclosure) is the physical barrier that separates a building's interior and exterior environments. Therefore, this envelope is responsible for creating a building's resistance to outside air, water, heat, light, and noise transfer.

There are several reasons that a living wall enhances the thermal performance of a building envelope. Most notably, this is due to the fact that a living wall requires a substrate system, which often contains a growing medium, for the plants to be attached to the wall.

One study has found that some living walls offer as much as a 68°F air temperature difference between the surface of the building envelope and the ambient air.

It’s not just a reduction in heat transfer that has researchers excited about the energy-reducing effects of a living wall on a building’s facade. During cold weather, living walls also limit the flow of heat from inside the building to the outside.

Research by the University of Plymouth has discovered that swapping an existing wall featuring a masonry cavity to one containing a living wall can lower the amount of heat lost through its structure by over 30 percent. This study found that the areas within a building that contained an exterior living wall remained more stable in temperature throughout the day. This meant that less energy was required to heat them.

When living walls on the facades of buildings are having such a significant effect as a buffer against both hot and cold weather, they allow a building to require less artificial heating and cooling, therefore lowering its energy usage.

The Ability to Pre-Cool Intake Air

Living wall facades also play a key role in pre-cooling intake air to improve the performance of HVAC (Heating, Ventilation, and Air Conditioning) systems. Firstly, the shading effect that the plants provide to the exterior of the building prevents it from absorbing solar radiation. In doing so, this solar radiation is also prevented from being re-radiated back into the surrounding environment of the building.

Secondly, the living wall encourages a process known as evapotranspiration, which cools the surrounding air. It also causes the formation of dew, which has an additional cooling effect on the immediate outside environment.

This means that when a HVAC system draws air in from its exterior intake vents, it is doing so with cooler air than what it normally would. This shift dramatically reduces the negative impacts of heavy energy loads on air conditioning systems — especially during extremely hot weather.

Recent studies also confirm these findings, with one report stating, “Green walls allow less costly heating, ventilation, and air conditioning systems in almost all climate zones. [They] will support the provision of indoor comfort in different climatic zones and the realization of comfort conditions at much lower costs, especially by reducing energy loads.”

More Efficient Solar Photovoltaic (PV) Technology

Research is also highlighting the positive effects a large surface area of plants can have on the efficiency of solar PV systems. In 2021, a study by an Australian university found that installing PV panels on a green roof can increase their output by around 3.6 percent when compared to a typical rooftop setup.