Soil-Based Green Roofs

Abstract

Although typically eschewed in favor of engineered substrate, natural soils can provide an important ecological benefit for green roof systems in terms of jump-starting a viable habitat. They can act as fungal and microbial inoculants and can serve as an additional source of plants and insects (via seed banks, eggs, and larvae), presumably of species that naturally coexist. Even when no longer biologically active, natural soils can still benefit roof systems by mimicking the mineral-based properties of the natural habitat of a particular plant palette. However, concerns of fine particle illuviation, increased roof loading, and unpredictable biological activity dampen use of natural soils on green roofs. This chapter discusses the pros and cons of natural soils versus engineered substrates and how their properties can affect green roof systems. A single case study is also presented of the soil-based green roof at the Botanical Research Institute of Texas in Fort Worth (USA) that used a mixed engineered substrate–natural living soil system to model a local short-grass limestone prairie barrens ecosystem.