Living wall systems, vertical structures where plants grow on building facades, are increasingly used to reduce energy demand, improve air quality, and bring nature into dense urban areas. A new laboratory study shows that a simple change to the growing substrate inside these walls could significantly improve their thermal performance. By adding biochar, a carbon-rich material made from plant waste, researchers found that living walls can provide better insulation while retaining moisture more efficiently.
The study, published in Biochar , examined how adding different proportions of biochar to green waste compost affects heat flow and moisture behavior in living wall substrates. Researchers tested three substrate mixes containing zero, 15 percent, and 30 percent biochar under controlled laboratory conditions, measuring thermal conductivity, thermal resistance, moisture content, and weight as the materials dried over time.
“Our results show that biochar can play a meaningful role in improving the thermal performance of living walls,” said Jack Morewood, corresponding author and researcher at the University of Plymouth. “When biochar content increased and moisture levels were moderate to low, thermal conductivity dropped substantially. This means less heat can pass through the wall.”
Thermal conductivity is a measure of how easily heat moves through a material. Lower conductivity means better insulation. The researchers found that at a typical substrate thickness of 100 millimeters, a mix containing 30 percent biochar could provide nearly double the thermal resistance of compost alone under realistic moisture conditions. This improvement could translate into lower heating demand for buildings fitted with living walls, especially during cooler months.
Moisture also played a key role. All substrates became more thermally conductive as they held more water, but the biochar-amended mixes behaved differently from compost alone. While biochar reduced the maximum amount of water the substrate could hold, it slowed down drying and helped stabilize moisture levels over time.
“Biochar changes how water is stored and released within the substrate,” explained Josh Batterham, lead author of the study. “It reduces overall saturation but improves moisture retention at levels that are beneficial for plants. This combination can reduce irrigation demand while also supporting insulation.”
The study also found that substrates with higher biochar content were lighter when fully saturated. Lower weight is an important practical advantage, since the load-bearing capacity of walls often limits where living wall systems can be installed.
Although biochar-enhanced substrates do not match the insulating performance of conventional building materials such as foam or mineral wool, the researchers emphasize that living walls provide multiple benefits beyond insulation alone. These include cooling through plant transpiration, air pollutant removal, biodiversity support, and improved urban microclimates.
“Living walls are not meant to replace traditional insulation,” said Steve Goodhew, co-author of the study. “But our findings show that their performance can be optimized. By tailoring the substrate, designers can reduce trade-offs between insulation, irrigation needs, and plant health.”
The authors note that moisture management is critical. Lower moisture levels improve insulation but may reduce cooling from evaporation during hot weather. This means biochar-enhanced substrates should be considered as part of an integrated design that accounts for climate, plant selection, and building use.
The researchers conclude that biochar has strong potential to improve the environmental performance of living wall systems and possibly other forms of green infrastructure, such as green roofs. Future work will explore long-term performance, different types of biochar, and real-world testing on buildings.
“This study provides practical evidence that small material choices can make a big difference,” Batterham said. “Biochar offers a promising pathway to make green building technologies more efficient, resilient, and sustainable.”
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Journal Reference: Batterham, J., Alencastro, J., Murphy, T. et al. Biochar to improve the thermal performance of living wall systems: laboratory assessment of three planting substrates. Biochar 8 , 10 (2026).
https://doi.org/10.1007/s42773-025-00508-5
About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
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Biochar to improve the thermal performance of living wall systems: laboratory assessment of three planting substrates
10-Jan-2026