Researchers at the University of Plymouth in the UK have published a study which found that overlaying living walls on existing buildings can improve thermal performance by 31%.

The findings arose from a live experiment on a campus building, where researchers added a living wall system to an uninsulated external masonry cavity wall. The cavity masonry wall has been one of the most common forms of construction across the UK, Europe, North America, and Asia since the 1920s, with cavity systems accounting for 70% of UK dwellings. In addition, 30% of the UK’s building stock does not have cavity insulation.

The Plymouth study is not the first to investigate the impact of living wall systems on such properties. One previous study cited in the paper found that living wall systems could yield energy savings during the UK winter period of between 21% and 37% compared to bare walls, while another found that in extreme cold weather conditions, the savings rise to between 40% and 50%.

In hot climates, meanwhile, living wall systems have been found to reduce the urban heat island effect. By minimizing solar gains on buildings through foliage shade on facades, living wall systems can reduce peak cooling loads on buildings by 28%, and lower wall surface temperatures by 11°C (51°F) according to research cited in the Plymouth study.

To further explore the thermal benefits of living walls on existing buildings, the Plymouth team capitalized on extensive renovations being undertaken to a campus office building in 2019, adding an externally planted living wall to a pre-1970s masonry construction. The new system consisted of a waterproof synthetic layer, absorbent moisture layer, and porous outer felt layer and makes use of these to form pockets for soil and planting. The wall was populated with local plant species including sedges, ferns, rushes, and flowering shrubs.

“Overall findings from this study led to the calculation of a U-value for this living wall system façade location, which was a 31.4% improvement over the original as built state of the same wall,” say the researchers. “Whilst this study is not representative of all situations and wall types, the findings suggest that adding a living wall system to the façade of an uninsulated cavity masonry wall could be used to lower heat losses in addition to bringing many other benefits, such as increased biodiversity, sound absorption and reductions in air pollution.”

The results are encouraging signs for architects engaged in the design and delivery of living wall systems. In August, as part of our Jobs Highlights series, we profiled a position at North Carolina-based firm Living Roofs Inc, who were searching for a Project Designer to assist in the design and installation of green roofs and living walls.

In 2019, as part of our Studio Snapshot series, we spoke with David Brenner, founder of the San Francisco-based firm Habitat Horticulture. “Living walls are often considered an afterthought or a static accessory in architectural design,” Brenner told us. “Having said that, the tide seems to be shifting with proactive urban greening policies and the rise in popularity of biophilic design. I think we are only scratching the surface in understanding the impact living walls can have.”