Site Conditions, Maintenance Costs, And Plant Performance Of 10 Extensive Green Roofs In The Research Triangle Area Of Central North Carolina

Compared with traditional roofing, green roofs (GRs) have quantifiable environmental and economic benefits, yet limited research exists on GR plant survival, maintenance practices, and costs related to plant performance. The objective of this study was to assess plant cover, site conditions, and maintenance practices on 10 extensive GRs in the Research Triangle Area of North Carolina. Green roof maintenance professionals were surveyed to assess plant performance, maintenance practices, and maintenance costs. Vegetation cover on each site was characterized. Relationships among plant performance and environmental and physical site characteristics, and maintenance practices were evaluated. Survey respondents ranked weed control as the most problematic maintenance task, followed by irrigation, pruning, and debris removal. No single design or maintenance factor was highly correlated with increased plant cover. Green roof age, substrate organic matter, and modular planting methods were not correlated with greater plant cover. Results showed a trend that irrigation increased plant cover. Plants persisting on GRs included several species of stonecrop (Sedum sp.), but flame flower (Talium calycinum) and ice plant (Delosperma basuticum) were also present in high populations on at least one roof each. Green roof maintenance costs ranged from $0.13/ft(2) to $3.45/ft(2) per year, and were greater on sites with more weeds and frequent hand watering.