Cooling Down Heated Cities through Moss

It is becoming increasingly hot in the Netherlands. This wee, too, brought a lot of heat. This is especially noticeable in cities, where the temperature difference with the countryside can be as much as 7 degrees. This is a consequence of urbanization, but greening urban areas often proves difficult in practice due to high costs and heavy maintenance. However, with the introduction of moss in the built environment, heat stress can be reduced, and greening becomes more accessible.

For years, the importance of greenery in cities has been emphasized. "The best thing municipalities can do is plant greenery," argues Jeroen Kluck, lecturer at the Hogeschool van Amsterdam. In practice, planting greenery can still be challenging. High maintenance and high costs mean that many parts of the city lack options for greening. "In neighborhoods with lower incomes and a lot of social housing, such as flats, the environment is often more urbanized. The possibilities for people to seek cooling in greenery also vary greatly per neighborhood," says Marian Stuiver of Wageningen University. An innovative solution to this is to deploy moss growth on the walls of buildings and infrastructure.

Moss and the Heated City

Currently, ivy is considered the most accessible way to grow greenery vertically, but now there are other options, such as moss concrete. Moss has several advantages over traditional climbing plants like ivy. First, moss requires significantly less maintenance; it does not need pruning and does not require complex structures to grow. Additionally, moss growth does not require planters because mosses have no roots. Thus, no precious space is taken up in the city. The result is a constant green layer that helps cool the city.

Wall Greening

Wall greening provides cooling, as a green wall retains less heat than a brick wall. Additionally, plants hold a lot more water, the evaporation of which quickly cools the air in the streets. A green wall also helps improve air quality by capturing particulate matter, which becomes more harmful in hot weather. Furthermore, it can contribute to urban biodiversity by providing habitat for insects and birds.

New in Construction

Until recently, moss was not an option in construction. The idea came from TU Delft and was further developed by Auke Bleij. He founded the start-up Respyre to make use of the advantages of moss and the low maintenance of the small plant. Meanwhile, the first moss walls can be seen in Limburg, Purmerend, and Alphen aan den Rijn. The introduction of this new alternative makes greening accessible to even more places in the city. The product can be applied to any paved wall. The effect is substantial: a gray wall can heat up to about 60 degrees, while a vegetated wall heats up to about 30 degrees—a huge difference.