Houseplants and more advanced plant systems, such as indoor living walls and hydroponic towers, have the potential to raise indoor humidity, boost thermal comfort and help create healthier, more climate-resilient buildings, according to new research led by the University of Surrey’s Global Centre for Clean Air Research (GCARE).

Published in Building and Environment, the study brings together an international collaboration of experts to examine how plants genuinely influence indoor environmental quality. While the understanding of outdoor urban greening has advanced, the effects of indoor green infrastructure have remained poorly defined.

To address this knowledge gap, researchers developed a ten-question framework that examines the evidence across technical, microbiological, health, socio-economic and place dimensions – offering the clearest picture yet of how different types of indoor greening perform in real buildings. The study also introduces the first clear comparison of 26 different indoor greening systems and how they impact indoor-environmental quality parameters, giving designers and building managers clearer guidance than ever on what actually works and where evidence is still lacking.

The analysis shows that larger indoor greening systems can make spaces feel up to two degrees cooler and more comfortable, even when temperatures remain the same. Some engineered systems help reduce fine particulate matter and volatile organic compounds, although the strength of these effects depends on plant density, lighting and overall design. The study also points to early evidence that greenery may enrich the indoor microbiome by introducing more environmentally derived microbes.

The study is a collaboration of 35 experts across the UK, Europe, USA, Australia, India, and Brazil through the GREENIN Micro Network Plus project.

Professor Prashant Kumar, lead author of the study is the founder of Surrey’s Global Centre for Clean Air Research and leader of the GREENIN Micro Network Plus project. He said:

“People spend around 90 per cent of their lives indoors, but surprisingly, we still understand very little about how indoor plant systems can reshape those environments. Our collaborative work shows that indoor greening can make a meaningful difference in certain situations – not just to how buildings feel, but to how they cope with heat, humidity and pollutants.

“But these benefits don’t happen by accident. They rely on using the right systems, in the right way, with the right lighting and maintenance. Treating greening as environmental infrastructure, rather than decoration, as well as filling substantial research gaps in the topic area, will be key to unlocking its full potential.”

The study also makes clear that more work is needed. Many older experiments used unrealistic numbers of plants or controlled chambers in labs that do not reflect real homes or offices. The authors argue that the next step is to carry out long-term, in-building studies that consider lighting, ventilation, occupancy and maintenance – the practical realities that determine whether indoor greening performs well over time.

Dr Tijana Blanusa, Royal Horticultural Society’s Principal Horticultural Scientist and co-author of the paper, said:

“Indoor planting is a fantastic way to bring the benefits of plants, and people’s interaction with them, into urban homes, schools and any other spaces where nature is not easily accessible. This paper lays strong foundations by providing evidence of the conditions needed to achieve the greatest impact on air quality, wellbeing and more.”

The research forms a core part of the GREENIN Micro Network Plus project, which brings together universities, local authorities, environmental organisations and horticultural experts to explore how indoor spaces can be designed for better air quality, comfort and wellbeing in a changing climate. It also lays important groundwork for future design guidance and policy based on what indoor greening can realistically achieve.

Led by the University of Surrey’s Global Centre for Clean Air Research (GCARE), in collaboration with the UK Centre for Ecology & Hydrology (UKCEH) and the Universities of Bath, Oxford, York, and Cranfield, GREENIN Micro Network Plus is funded by the EPSRC under the Grant No. APP55977.

Reference:

Kumar, P., et al. (2026). Ten Questions on Indoor Greening and Environmental Quality. Building and Environment 294, 114336. https://doi.org/10.1016/j.buildenv.2026.114336

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