Green walls can offer more than an environmental finish to a wall – they can significantly improve acoustics, a study has found.

To date, green walls have been recognised more for their climatic benefits – helping to conserve energy, improving air quality and mitigating the urban heat island effect, along with bringing about a sense of well-being.

Now, agricultural engineer Zaloa Azkorra of the University of the Basque Country’s Department of Thermal Engineering has found that when installed correctly, green walls can also provide passive acoustic insulation.

Azkorra’s study was prompted by the lack of credible research available that recognised the acoustic properties of green walls. She decided that no current study offered any strong conclusions on the topic and deduced to conduct a laboratory experiment in a controlled environment.

The study was carried out within a reverberation chamber in two different labratory settings that follow international standards. A modular green wall was used.

Modular green wall used in study

Azkorra concluded that “the green wall showed a similar or better acoustic absorbtion coefficient than other common building materials, and its effects on low frequencies were of particularly interested because its observed properties were beter than those of some current sound-absorbent materials at low frequencies.”

“The main results were a weighted sound reduction index (Rw) of 15db and a weighted sound absorption coefficient (a) of 0.40. It could be concluded that green walls have significant potential as a sound insulation tool for buildings but that some design adjustments should be performed, such as improving the efficiency of sealing the joints between the modular pieces,” Azkorra said.

The voice frequency was listed at around 60 decibels, corresponding to the frequency at which this modular green façade is more efficient absorbing sound. Azkorra suggests this points to new uses for green walls in public places such as restaurants, workplaces and hotels.

There is also a huge opportunity for green walls to exercise their acoustic benefits in healthcare environments, where they can offer biophilic benefits and support sound reduction, both of which can be critical to patient recovery.

Libraries could also stand to benefit from green walls’ sound-dampening qualities, as demonstrated in a recent project by Australian green roof and wall specialists Junglefy.

The green wall Inside Bankstown Library

Junglefy installed a 9.5 metre high green wall inside Bankstown Library last October. The wall features 4,353 plants from 10 species, and while it has been installed primarily for its carbon absorbing benefits, the size and plant variance of the wall can also support the acoustics within the building.

US green wall company Green Over Grey also lauds the use of plants within buildings for their acoustic benefits.

“In Germany a green concert hall was constructed which incorporated many plants,” the firm state on their website. “The high density resulted in such a good acoustic quality that the German Broadcasting Station relocated to use the room for news casting,” the company said.

Ambius Indoor Plants has also conducted its own research in the UK. With additional studies conducted by Peter Costa of South Bank University in London, Ambius has concluded that plants can be effective at reducing background noise, with species selection and positioning crucial to achieving the proper effects.

Despite the myriad benefits, cost seems to impede designers, who aren’t rushing to implement green walls for clients.

In an article with Science Daily, Azkorra recognised that green wall systems and their maintenance are costly and acknowledged that there is plenty of room for improvement.

Australian ecological artist Lloyd Godman, who is conducting a plant experiment atop Eureka Tower, noted that many green walls fail due to maintenance costs. He estimates that those costs for a typical vertical garden are equivalent to approximately 20 per cent of its installation price per year.