Use of Repurposed Fibers to Decrease Hydraulic Conductivity without Compromising Load Restrictions in Urban Roof Farms

Rooftop farming systems deliver the benefits of rural and suburban agriculture to an urban setting by taking advantage of seldom-used roof real estate. One of the challenges preventing the industry from reaching a bigger audience is the existing building’s roof ability to withstand additional structural loads imposed by soil, vegetation, retained water, and increased activity. To help minimize added structural loads designers have used lightweight engineered soil to mimic the characteristics of natural soil. However, lightweight engineered soils have poor water retention properties which leads to the need for heavy irrigation schedules, which in turn leads to rapid leaching of nutrients. This imposes an economic deterrent to the wider use of this green technology. The conundrum leaves the designers and/or farmers with the difficult choice of sacrificing soil depth available for plant growth by adding heavier fine grained soils; or, planning for heavy irrigation schedules accompanied by nutrient loss which results in added economic liability. Through laboratory experiments, the authors have found results which indicate that the addition of repurposed textile to lightweight engineered soils has the effect of modifying the hydraulic properties of the soil without compromising its weight. The results of our experimental program are presented as well as the implications on imposed roof weights, loss of nutrients, and economic benefits of adopting the technology. By presenting this work to the geotechnical community the authors intend to create awareness to this niche technical area, where soil mechanics and structural knowledge can be used to solve problems faced by agronomists.