Acoustic insulation in the form of lush green walls is a sound approach every landlord should consider.
Phone chatter, obnoxiously loud conversations in adjacent cubicles (we've all been there,) printers, photocopiers, HVAC systems... all distract and make employees less efficient. There are several ways to remedy noise levels in the workplace - sound absorption and sound masking are increasingly popular strategies, but what about living plants?
In 2015, an agricultural engineer of the University of the Basque Country conducted a research on the benefits of green walls as passive acoustic insulation for buildings. Zaloa Azkorra concluded that “the green wall showed a similar or better acoustic absorption coefficient than other common building materials, and its effects on low frequencies were of particular interest.”
Despite a rising number of studies highlighting the acoustic potential of plants, biophilic design is a resource yet to be explored by acousticians, particularly in sectors like the workplace, still in dire need of fine tuning.
NB: Biophilia refers to the innate love for the natural world, in other words, for nature and the outdoors.
How do plants regulate noise in the workplace?
To understand this, we must first brave the acoustic jargon and grasp the meaning of reverberation time.
Let's get technical for just a sentence. Reverberation time refers to the time it takes for a sound wave to die away to a level 60 decibels below its original level. And now, in English: when a source creates a sound wave in a room, what you hear is not only the sound wave spreading directly from the source, but also the sound reflecting from various surfaces around you.
Let's put this in context. The average reverberation time (now that you're an expert, we can call it RT) in an open plan office should be less than 1 second. In an enclosed office, the recommended RT is less than 0.6 seconds. In a meeting room, 0.6-0.8 seconds. What does this mean? Simply that an open plan office sporting an RT of 0.6 seconds will be significantly quieter than one with an RT of 0.9 seconds.
But how exactly can plants help reduce reverberation time, and therefore noise levels, in your office?
When sound hits a masonry wall, it bounces off the rigid surface and back to its source, like a solitary tennis ball between a racket and the wall. In contrast, when a sound wave hits a plant, the flexible surface will vibrate and transform sound waves into other kinds of energy. This is the same principle behind acoustic panels that absorb sound by converting sound energy into heatwaves.
There is a clear correlation between the way sound behaves and the surfaces around it. Think of a home with a carpet versus a home with solid floors. Usually, a carpeted room will prevent the sound from bouncing all over and creating echoes. Much like a carpet, plants and shrubbery are naturally uneven - covering surface areas with greenery will help accomplish the same feat. Think vines on walls, lawns, green walls, moss walls, etc.
How to use plants to reduce noise?
Rough bark and leafy plants are particularly effective but for maximum acoustic potential, you should also consider number of plants, location, size and surface area.
Larger planters contain more compost and provide more space for greenery. Combined, these two have a significant impact on noise reduction. As a result, your office benefits from better acoustics, and cleaner air. It's a win-win.
Tip: For better acoustics, arrange your planters throughout the space as opposed to clustering them. It's all about that surface area - the more spread out your plants are, the more opportunites there are for sound diffusion.
Focus on corners, edges and walls
Along the same principle, plants placed in the periphery of your office - corners, edges, walls - are more likely to reflect sound than plants placed in the middle.
Replace partitions with plant screens
Offices are inherently loud - open plan offices even more so. Oftentimes, this means partitions or rows of filing cabinets. What if you could use plants instead? Effective in reducing noise, and more attractive than your average office partition, plant screens are a great alternative.
If your tenants are reluctant to lose the filing cabinets, these and other surfaces can also be used to place small bushy plants in narrow containers.
Biophilic design guidelines for good acoustics
If utilised strategically, biophilic design can drastically improve acoustics in the office and its common areas.
There are few studies on the relationship between plants, architecture and acoustics. In a study performed by P. Costa of the South Bank University in London (1995,) Costa tested several single potted plants and combinations of plants in various areas in a room. His conclusions amount to a certain number of guidelines covered above.
If you accidentally skipped to this last paragraph, here's a summary:
- Plants need to be large and healthy
- Plants should preferably be leafy
- Arrangements with a minimum of three plants seem more efficient than single plants
- Spread out arrangements are better than a concentrated few plants.
- Placing plants alongside walls has a greater impact on acoustics than if they're placed in the middle of a room