<p>Benefits include improved storm water management, energy conservation, reduced noise and air pollution, improved biodiversity, and even a better return on investment than traditional roofing. <br /><br />But a healthy roof requires a plant species that can survive extreme climates and propagate easily to reduce erosion and weed growth. <br /><br />Kristin L. Getter, Michigan State University (MSU) horticulturist, conducted a study to determine the effect of the soil depth on success of green roofs. The research focussed on Sedum, a variety of succulents known for its drought tolerance. <br /><br />Plots were constructed using the drainage mats and waterproofing systems typical of green roofs, but the growing material varied in depth -- four cm, seven cm and 10 cm. <br /><br />Twelve species of Sedum were planted, fertilised, and watered once. The moisture of the growing material was measured at random times each week. <br /><br />Plants were monitored over four years. Since the average lifespan of the inorganic components of a green roof is about 45 years, the researchers determined that it was important to study the longevity of the plants. <br /><br />The study found that the shallowest plot had the lowest moisture levels on average and dried the fastest after a rain. At the four-cm depth, four species failed to exhibit significant growth over the four-year period. <br /><br />Results indicate that, for the surviving and most-abundant species, no benefits accrue in case of depths more than seven cm, but make for lighter roof loads, says an MSU release. <br /><br />"However, at deeper depths, these plants would likely be healthier, contain greater biomass, and be less susceptible to adverse environmental conditions," says Getter. <br /><br />The study was published in HortScience. </p>
<p>Benefits include improved storm water management, energy conservation, reduced noise and air pollution, improved biodiversity, and even a better return on investment than traditional roofing. <br /><br />But a healthy roof requires a plant species that can survive extreme climates and propagate easily to reduce erosion and weed growth. <br /><br />Kristin L. Getter, Michigan State University (MSU) horticulturist, conducted a study to determine the effect of the soil depth on success of green roofs. The research focussed on Sedum, a variety of succulents known for its drought tolerance. <br /><br />Plots were constructed using the drainage mats and waterproofing systems typical of green roofs, but the growing material varied in depth -- four cm, seven cm and 10 cm. <br /><br />Twelve species of Sedum were planted, fertilised, and watered once. The moisture of the growing material was measured at random times each week. <br /><br />Plants were monitored over four years. Since the average lifespan of the inorganic components of a green roof is about 45 years, the researchers determined that it was important to study the longevity of the plants. <br /><br />The study found that the shallowest plot had the lowest moisture levels on average and dried the fastest after a rain. At the four-cm depth, four species failed to exhibit significant growth over the four-year period. <br /><br />Results indicate that, for the surviving and most-abundant species, no benefits accrue in case of depths more than seven cm, but make for lighter roof loads, says an MSU release. <br /><br />"However, at deeper depths, these plants would likely be healthier, contain greater biomass, and be less susceptible to adverse environmental conditions," says Getter. <br /><br />The study was published in HortScience. </p>
