Flammability and Reaction to Fire of Different Plant Species Intended as Vertical Greenery on Building Façades

Vertical greenery or green walls are spreading rapidly not only in Southeast Asia but also in colder regions such as Western and Central Europe. The simultaneous growth and densification of larger cities has accelerated this trend recently as these cities require increased green space to improve living quality. A significant issue directly affecting security aspects regarding building components covered with different kinds of plants is their fire behaviour. A major parameter expected to influence this behaviour is the moisture content of the plants and their ability to retain moisture in case of irrigation interruption. In this study, four different plant species were chosen due to their hardiness which favours their usage as vertical greenery under the climatic conditions of Central Europe. Bomb and cone calorimetric investigations and single-flame source tests were carried out on them. These tests have been executed at different plant moisture contents as the fire behaviour of plants is obviously influenced by their moisture content. The results quantify the remarkable individuality of the plants with respect to their reaction to fire exposure in both moist and dry conditions. The findings can be extrapolated to quantify the overall fire behaviour of a green façade, especially the accruing heat content. Additionally, an optimized position of different plants within the façade can be derived to reduce the flame propagation probability upward of the façade.