Biophilia has long been recognised as a key ingredient in the holistic design of indoor spaces, but few of the general beliefs about the benefits of plants in these environments are supported by science.
Biophilia and indoor environmental quality
Recently, academic and mainstream publications have reported that, despite widespread belief of the contrary, single potted plants alone are unable to remove enough pollutants to improve indoor air quality. This is true, at least from the scientific evidence the academic community has collected so far. However, they cannot say this with certainty because not every plant or pollutant has been tested under all environmental conditions.
Research has now moved onto green walls, and especially what is known as active green walls, which boast a higher density of plants and increased airflow through the soil. This airflow drags pollutants through the soil – where most of the removal is achieved – and cleans the air much more effectively at the same time. But this research is at a very early stage, and although results look very promising, having active green walls has a significant cost implication and this makes them unsuitable for many domestic environments. Further to this, plants have also been shown to increase humidity indoors via the natural process of transpiration which releases water vapour into the air and effectively turns them into passive and low energy humidifiers.
But plants can do so much more than just improve everyone’s indoor environmental quality. They have also been shown to have benefits to physical and mental health, mood, productivity and comfort in a range of different industries.
In a 1989 paper, psychologist Rachel Kaplan suggested the theory that nature can provide a restorative effect to attention after mental fatigue. Known as the biophilia hypothesis, Kaplan’s theory suggests that the tendency of humans to focus on and affiliate with nature is genetic.
It has now been applied to indoor plants in an office environment in several scientific studies, but with mixed results. The inconsistencies are thought to occur in the experimental design and the fact that the indoor environments studied were not nature stimulating enough to trigger attention restoration, which has been shown to work in more immersive outdoor surroundings.
Biophilia and productivity
Creating a workplace that facilitates optimal performance and better productivity is a heavily researched and multi-million-pound industry. ‘Performance’ encompasses any task testing human intellect, which can include creativity-based activities and the testing of word association, filing and sorting. Research across several universities in Japan found that indoor plants can improve the results from performance tasks, but any improvement is task type dependent. The reasons for this are not clear, but the fact that it’s not consistently the same tasks affected, suggests the problems may lie with the experimental design and not the plants themselves. Suggestions have also been made by researchers in Denmark that the condition of the plant can have an impact, and that if the plant is not in optimal condition, little productivity-based improvement will be elicited.
Biophilia and Mood
Plants are well known to invoke positive feelings, and a workplace filled with biophilia is certainly much nicer to work in, but is there any science to back this up? Plants have been shown by researchers at the University of Copenhagen and collaborating universities across Japan to reduce stress by enhancing coping strategies (i.e. through maintenance) and also to improve the general mood and positivity of participants. Interestingly, the extent of the effects was found to be dependent on the gender of the participants tested and whether the plant was flowering.
Biophilia and Health Care
The presence of biophilia in hospital environments has been shown to invoke an array of beneficial responses in patients and staff. In patients, the placement of plants within their rooms has been found to improve recovery times post-surgery and general pain levels (meaning fewer painkillers are required), reduce anxiety, fatigue and even shorten hospitalisation times.
Researchers at the University of Twente in the Netherlands observed that even participants presented with a hypothetical situation of hospital admittance found that when shown a picture of their treatment room, rooms including plants reduced stress levels.
Similar benefits have been observed by researchers looking at in care homes in Finland, where workers looking after residents with dementia noticed a prominent improvement in their psychological and social wellbeing when indoor plants were introduced. This has now led to numerous gardening schemes being implemented across care homes in the UK.
In today’s office environments workers are often isolated from the numerous benefits provided by natural systems and processes. Biophilic design facilitates this connection via the integration of various features into the office space, including indoor plants, natural materials, circadian lighting and the use of patterns and shapes from nature.
This enhanced connection has been shown to improve cognitive function and focus, boost mental stamina and attract the top talent. A recent global survey by Human Spaces reported that 33% of respondents felt the physical environment was a key driving factor when looking for a new role.
Biophilia and Cooling
The ability of external green façades to provide cooling, which in turn reduces the thermal load on buildings and energy requirements is well established. Similarly, utilising green walls indoors has been shown to provide significant cooling, with an average reduction of approximately 3.5 °c measured across several studies in the vicinity of the wall. More work needs to be undertaken to understand how much of an effect this has across a floor plate, but utilised correctly this could provide significant energy savings, made even more relevant with the rise of net zero carbon.
It’s worth noting that plants should not be considered as a single entity expected to provide all of the above described benefits. Differences between species provide large performance variability, and it’s therefore recommended that experts be consulted to ensure that optimal performance is achievable through correct environmental conditions and choice of plant species. Furthermore, although some of the benefits of indoor plants are less clear, when considered holistically, they should certainly be considered a pre-requisite for any building type.
Curtis Gubb joined Cundall in October 2019 and has contributed to the sustainability team’s ongoing research into IEQ in the workplace and managed several ongoing monitoring projects. As part of Cundall’s air quality team, he has undertaken ambient assessments and written strategies for clients on how to enhance indoor air quality. He is an Environmental Health PhD candidate from the University of Birmingham and also a member of the CIBSE air-quality working group.
Work in Mind is a content platform designed to give a voice to thinkers, businesses, journalists and regulatory bodies in the field of healthy buildings.