Life Cycle Cost Analysis of Extensive Green Roofs in Switzerland and the Netherlands

Extensive green roofs in Switzerland and the Netherlands are economically sustainable when considering the added energy savings, municipal incentives and storm water fee reductions. By combing surveys, interviews, and reviews of municipal regulations for fifteen projects the Life Cycle Cost (LCC) was calculated by discounting green roof cash flows over a 50 year time period to determine a Net Present Value (NPV). This research finds that an extensive green roof NPV in Switzerland costs 27% - 37% less than a conventional flat roof. Similarly in the Netherlands, the NPV of green roofs is determined to be 16% - 26% less than a conventional flat roof. Presented here is summary of the results and the explanation of local influences of municipal incentives.

Kelp Extract (Ascophyllumnodosum) Can Improve Health and Drought Tolerance of Green Roof Plants

The soil additive Ascophyllumnodosum (Norwegian kelp) can increase drought tolerance of plants, and promote seed germination, yet there has been no published research testing this amendment on green roofs. Liquid A. nodosum extract in two volumes and a slow release fertilizer were tested in a pot culture experiment for annuals, perennial cultivars, and three native species. Kelp extract did not improve the germination percentage of any of these species. In drought conditions both on a green roof and in the greenhouse, kelp treatments increased plant biomass relative to controls for some species only; plant health and longevity weregenerally improved when kelp was applied as an amendment. Soil water content was higher in kelp treated pots compared to fertilizer treated pots, and higher than controls in kelp treated pots for some species. Application of this local renewable resource to green roof plants could help to improve plant and substrate health while improving drought tolerance of plants on green roofs.

Controlling Ivy Attachment to Wall Surfaces by Applying Paints, Metal Meshes and Sheets

Growing ivy around buildings has benefits. However, ivy potentially damages buildings which limit its use. Options for preventing ivy attachment were investigated to provide ivy management alternatives. Indoor and outdoor experiments were conducted, where metals (Cu, Zn) and anti-graffiti paints were applied to model wall panels. Metal treatments, in both indoor and outdoor experiments, fully prevented ivy attachment. For Hedera helix, silane-based antigraffiti paint prevented attachment in the laboratory and required under half the peak detachment force necessary to detach the control in the outdoor experiment. In conclusion, metals and silane-based paint are management possibilities for ivy attachment around buildings.

Green Roof Plant Trials for the Central Great Plains

Forty-three taxa representing native and adaptable plants were trialed for 4 years on an irrigated
(as needed) 15 cm (6 inch) deep extensive green roof in Lincoln, NE. Twenty-three of the taxa
showed good performance with minimal maintenance. At the end of the trial in fall 2014, 32 of
the taxa still had at least one specimen surviving. Drought impacts in the trial’s second year
eliminated several taxa. Presented here are results and the positive findings of four new extensive
green roof taxa, Festuca cinerea, Carex glauca, Eragrostis trichodes, and Distichilis spicata

Observation of Biodiversity on Minimally Managed Green Roofs in a Tropical City

While much of the land in Singapore has been urbanized, green roofs have the potential to be part of an urban ecosystem where limited human interference can promote natural processes. This study observes the establishment of flora and fauna communities on two newly installed green roofs using a mix of seeding, transplantation and spontaneous colonization installation methods and operating under minimal management over a period of 16 months. Recorded here are plant compositions and spatial distributions of flora growth of 64 species over this period. The minimally managed green roofs in this study possess increased plant species richness, highlighting a way to enhance urban diversity in a tropical city.

Insect Communities On Green Roofs that are Close in Proximity but Vary in Age and Plant Coverage

The effects of roof age and plant coverage on insect communities were investigated between three green roofs located on the campus of Southern Illinois University Edwardsville. Insect collections were made using pitfall traps on green roofs that were established between 0.5 month and five years prior to insect collection. The green roof with the greatest insect collection rate was the oldest but intermediate in size and percent plant coverage. The oldest green roof had similar collection rates as a nearby ground-level rain garden; however measures of species diversity and evenness were greater in the rain garden.

Substrate Loss is Minimal in Vegetated and Un-vegetated Extensive Roof Modules Over a 14-Month Period

The presence of vegetation is thought to reduce loss of soil substrate after roof installation; however, few attempts have been made to quantify this effect. Twelve green roof modules placed at a 2% slope were used to quantify the effect of wind, precipitation intensity, vegetation and vegetation type on modular green roof substrate depth. The presence of vegetation reduced substrate loss immediately after installation of equipment, yet had little effect on substrate depth once the substrate had settled. Neither wind speed nor precipitation rate had a direct effect on substrate depth, although after some large rainfall events substrate depth increased due to media expansion caused by the retained water. Overall we observed negligible substrate depth decrease, regardless of vegetation presence, wind speed or precipitation intensity.

Native Forbs Produce High Quality Seeds on Chicago Green Roofs

Although a paucity of bees on Chicago green roofs suggests some plants may experience reduced pollination and thus poor seed production, a previous investigation revealed high seed set in green roof plants. However, high quantity of seeds does not always imply high quality. In this study, we compared seed germination between green roof and ground-level locations. We hypothesized that forb seeds from green roofs would have lower germination due to differences in maternal provisioning and environmental stressors. We found that green roof seeds did not have lower germination; this supports the continued use of native forbs on green roofs.

Vegetation Characteristics of Green Facades, Green Cloaks and Naturally Colonized Walls of Wooden Barns Located in the Mid-Atlantic Region of North America

We quantified the amount and diversity of vegetation on ten green facades and compared it to nine naturally colonized wooden barns located in the humid temperate climate of eastern North America. The leaf area index (3.3 m 2 -vegetation/m2 -wall) and canopy thickness (61 cm) of the green facades was nearly identical to that of the barns (3.1 and 69 cm), indicating that green facades mimic nature’s architecture. Predicting the biomass of façades from models developed for the barns’ canopies, indicated they should range from 1000 to 1400 g/m2 (5600 to 8000 g/m2 , fresh weight) but could be as much as 2900 g/m2 (21,000 g/m2 fw). The façades included a total of 14 vine species while the barns included 8. There was an average and maximum of 3.2 and 6 species on the facades and 2.3 and 4 on the barns. The biodiversity of the cultivated system closely mirrors the colonized system, suggesting that an optimum biodiversity may exist for vertical, vine based living architectures.

Observations on the Survival of 112 Plant Taxa on a Green Roof in a Semi-Arid Climate

The Denver Botanic Gardens (DBG) green roof, built in November 2007, is the first green roof on a city owned building in Denver, Colorado. To date, 112 plant taxa have been trialed, observed, and described on this low water green roof in the high and dry climate of the Colorado Front Range. Plant taxa survival was documented based on the original number of plants installed, and the surviving plants were rated on a scale of 1-4. Additionally, in 2011-2013, plant heights and widths were recorded. The data indicate that taxa can be grouped into categories of perish, survive, and thrive.

Aesthetics for Green Roofs and Green Walls

Do green roofs and green walls have aesthetic benefits? Most green roof proponents would say so. But what are they and how do they relate to green roof design in terms of species selection, planting arrangement, viewable context, access, maintenance and other factors? Aesthetics according to the Green Roof Design 101 Manual 2nd Ed (GRHC 2006) provides “pleasure- and psycho-physiologically-oriented benefits” but, this narrow understanding suggests that the aesthetic potential of green roofs is limited to what one might experience looking upon any garden. We suggest other ways that need exploring to make aesthetics more relevant and understandable to the practice of wall and roof greening.

We suggest other ways that need exploring to make aesthetics more relevant and understandable to the practice of wall and roof greening.

Living Architecture and Biological Dispersal

Many vegetative roof systems deliver biodiversity and conservation goals, but it may be less appreciated that roofs function as a nursery, exporting biological materials. Interestingly, we have observed one green roof performing two forms of plant dispersal, thus demonstrating the potential for vegetative roofs to offer nursery services to their surroundings. We describe the project, explain the dispersal strategies, provide a brief discussion, and define the terminology of terrestrial-roof link, agent dispersal, and self dispersal, in an effort to aid in understanding the nursery function of green roofs. Continuing and future research on the dispersal mechanisms of the roof are also briefly discussed.

Development and Features of the Green Roof Energy Calculator (GREC)

A data base-driven web tool has been developed from detailed energy modeling simulations to enable green roof practitioners to explore the energy, water, and urban climate implications of design decisions. Provided with basic characteristics of a green roof project, the Green Roof Energy Calculator performs a multi-layered interpolation within a database of 8000 simulations to estimate whole building energy use, storm water runoff, and sensible and latent heat exchange with the urban atmosphere. Output from each user query produces information for the specified green roof system, but also includes information for alternatives of both white and dark membrane roofs.

Seeding Green Roofs with Native Grasses

During six years of native grass establishment and growth on four green roofs, we sought to understand appropriate seeding seasons and spacing, the amount of time to reach the industry 80% coverage threshold (FLL 2008), the seed yield projections for volunteer plant infill. We also produced and tested methods for successfully and inexpensively seeding and determined “as needed” irrigation protocols. The suite of techniques examined improves and enhances the use, establishment, and management of native grasses on green roofs and reduces green roof costs. 

Plant Species Survival on Three Water Conserving Green Roofs in a Hot Humid Subtropical Climate

The quantification of ecological services from green roofs in Texas is emergent and proving advantageous. Identification of candidate plant species for green roofs in Texas and similar hot and humid subtropical climates is limited. Three extensive green roof systems and research sites in Texas employed different water conserving techniques ranging from no irrigation, to sparse application during dry and drought periods, to frequent watering with harvested rainwater. Thirty-four candidate species were identified for hot and humid climates from among the three sites. These findings help to establish a reference point for future investigations of green roof plant survivability.

Rethinking Extensive Green roofs to Lessen Emphasis on Above-Ground Biomass

In the future, most green roof applications will not be highly visible, yet these roofs will still provide the benefits of heat island reduction, stormwater control and biodiversity for hard-surfaced cities. However, human bias in wanting more biomass and visible blooms leads green roof horticulturalists and their approach of maximizing those aspects down a slippery slope that, in turn, leads to increased hours of labor, over-watering and fertilizing and specifying too many cultivars.

Fertility Management for Tomato Production on an Extensive Green Roof

Green roofs offer an alternative growing space to provide fresh vegetable products to urban
markets. The soil component is an important aspect of efficient green roof production systems
and adequate fertility levels are often lacking in media that are required to maximize plant
growth. This research project evaluated four fertilizer treatments on „Bush Champion II‟ tomato
(Solanum lycopersicum) growth and yield in a 7.62 cm green roof production system: (1)
vermicompost tea, 2) Miracle-Gro fertilizer, 3) Organic Miracle-Gro fertilizer, and 4) no
fertilizer. Treatments were applied weekly and ripe tomato fruit was harvested from June to
August. Results indicated that Miracle-Gro® provided the highest total tomato fruit yield, which
was 30% and 50% more in 2011 and 2012, respectively, compared to the next highest treatment -
Organic Miracle-Gro®. Plant vigor, chlorophyll content, and tomato yields indicated that
tomatoes can be successfully grown in a 7.62 cm green roof medium when given adequate
fertilizer applications.