The MSU research team
Associate Professor, Geography
Rique Campa, Professor,
Fisheries and Wildlife
Associate Professor, Civil and Environmental Engineering
Professor, Landscape Architecture
Indrek Wichman, Professor,
Graduate Research Assistant, Horticulture
PhD Graduate Research Assistant, Horticulture
Erik Cronk, Graduate Research Assistant, Environmental
Carly Eakin, Graduate Research Assistant, Fisheries and Wildlife
Graduate Research Assistant, Environmental Design
Kevin Krogulecki, Graduate Research Assistant, Environmental Design
Theresa Miller, Graduate Research Assistant, Environmental Design
Jeremy Monsma, Graduate Research Assistant, Environmental Design
What is a green roof?
An extensive green roof covers the garage providing an aesthetically pleasing view for the building occupants (Photo courtesy of Behrens Systementwick
An intensive green roof atop the Coast Plaza Hotel in Vancouver, British Columbia, has the appearance of a wooded forest.
Green roofs involve growing plants on rooftops, thus replacing the vegetated
footprint that was destroyed when the building was constructed. Germany is
widely considered the leader in green roof research, technology and usage. It is
estimated that 12% of all flat roofs in that country are green and the German
green roof industry is growing 10% to 15% per year. Modern green roofs can be
categorized as ‘intensive’ or ‘extensive’ systems depending on the plant
material and planned usage for the roof area. Intensive green roofs utilize a
wide variety of plant species that may include trees and shrubs, require deeper
substrate layers (usually > 10 cm (4 in)), are generally limited to flat roofs,
require ‘intense’ maintenance, and are often park-like areas accessible to the
general public. In contrast, extensive roofs are limited to herbs, grasses,
mosses, and drought tolerant succulents such as Sedum, can be sustained
in a shallow substrate layer (< 10 cm (4 in)), require minimal maintenance, and
are generally not accessible to the public.
Benefits of green roofs
A typical ugly commercial roof that provides no ecological, economic, aesthetic, or psychological benefits.
Flowering sedum and Allium schoenoprasum on a roof in Amsterdam.
As our forests and agricultural lands are replaced with impervious surfaces due
to urban development, the necessity to recover green space is becoming
increasingly critical for the health of our environment as well as our
well-being. Vegetated or green roofs are one potential remedy for this problem.
Establishing plant material on rooftops provide numerous ecological and economic
benefits including stormwater management, energy conservation, mitigation of the
urban heat island effect, increased longevity of roofing membranes, as well as
providing a more aesthetically pleasing environment to work and live. The
mitigation of stormwater runoff is considered by many to be the primary benefit
because of the prevalence of impervious surfaces in urban areas. The rapid
runoff from roof surfaces can exacerbate flooding, increase erosion, and may
result in raw sewage that is discharged directly into our rivers. The larger
amount of runoff also results in a greater quantity of water that must be
treated before it is potable. A major benefit of green roofs is their ability to
absorb stormwater and release it slowly over a period of several hours. Green
roof systems have been shown to retain 60-100% of the stormwater they receive.
In addition, green roofs have a longer life-span than standard roofs because
they are protected from ultraviolet radiation and the extreme fluctuations in
temperature that cause roof membranes to deteriorate. Furthermore, the
construction and maintenance of green roofs provide business opportunities for
nurseries, landscape contractors, irrigation specialists, and other green
industry members while addressing the issues of environmental stewardship.
Green Roof Research at Michigan State
An overview of the
research platforms at MSU.
The green roof research program at MSU was initiated in
collaboration with Ford Motor Company during 2000 in an effort to advise them on
the installation of a 10.4 acre extensive green roof on a new assembly plant in
The objectives of our ongoing research are to evaluate
plant species, propagation and establishment methods, plant succession, carbon
sequestration potential, water
and nutrient requirements, water quality and quantity of stormwater runoff, and
energy consumption. Numerous experiments are currently being conducted on the
roof of the Plant and Soil Sciences Building (PSSB), on the roof of the
Communication Arts Building (CAB), in the Plant Science Greenhouses (PSG), and
on 48 roof platforms at the Horticulture Teaching and Research Center
(HTRC) at MSU. The roof of the PSSB is equipped with heat flux sensors and
thermocouples that are measuring heat flow through the roof envelope and
temperatures above the roof, at various depths in the growing substrate, and
inside the building. On CAB, long-term plant survival, persistence, and
succession are being studied at various substrate depths in the sun and shade.
At the HTRC site, electronic tipping buckets record the volume and rate of
stormwater runoff from individual platforms. All sites are equipped with a
weather station and a datalogger that records measurements every five minutes,
24 hours a day.
Specific research objectives are to:
- Conduct a performance evaluation of specific plant species for rate of
establishment, nutrient requirements, environmental tolerances, plant
competition, ability to exclude invasive weeds, and survival and
- Evaluate mixed plant communities and succession over time.
- Examine differences in evapotranspiration rates, substrate moisture
levels, and plant performance among species exposed to several substrate depths
and various levels of drought.
- Utilize chlorophyll fluorescence measurements to quantify plant stress
before it is evident from visual observations.
- Determine effect of rooftop microclimate on winter damage and subsequent
the carbon sequestration potential of green roofs.
Quantify the differences in water retention among roof vegetation types.
- Quantify the differences in water retention among combinations of green
roof slopes and substrate depths.
- Evaluate the influence of roof vegetation on roof membrane temperatures,
heat flow into and out of the building, and energy consumption.
Public relations: provide visibility regarding green roofs.
Ongoing research studies
studying native species.
with Sedum cucurbita ‘Watermelonii’.
potential green roof species.
Within the platform partitions, three groups of plants
were cultivated to evaluate the effect of drainage system on plant
establishment, growth, and survival. One group consisted of seven Sedum spp. propagated from seed. Taxa included
S. acre, S. album, S.
kamtschaticum, S. ellacombeanum, S. pulchellum, S. reflexum,
and S. spurium ‘Coccineum’. Seed was applied at a rate of 1.0 g×m-2
and was mixed with 250 ml×m-2
of dry sand to ensure even distribution. All seed was obtained from Jelitto
Staudensamen, GmbH (Schwarmstedt, Germany). A second group consisted of two Sedum
spp. planted from plugs (116.3 cm3, 38/flat): S.
middendorffianum ‘Diffusum’ and S. spurium ‘Royal Pink’.
These plugs were supplied by Hortech, Inc. (Spring Lake, MI) and the study
contained 108 plugs of each taxa. The third group consisted exclusively of 18
taxa of Michigan native plants: Agastache foeniculum (lavender hyssop),
Allium cernuum (nodding wild onion), Aster laevis (smooth aster),
Coreopsis lanceolata (lanceleaf coreopsis), Fragaria virginiana
(wild strawberry), Juncus effusus (spikerush), Koeleria macrantha
(junegrass), Liatris aspera (rough blazingstar), Monarda fistulosa
(bergamot), Monarda punctata (horsemint), Opuntia humifusa
(prickly pear), Petalostemum purpureum (purple prairie clover), Potentilla anserina (silver feather),
Rudbeckia hirta (black-eyed
Susan), Schizachyrium scoparium (little bluestem), Solidago rigida
(stiff goldenrod), Sporobolus heterolepis (prairie dropseed), and Tradescantia ohiensis (spiderwort). All native plants were planted from
plugs (150.8 cm3, 38/flat) obtained from Wildtype Nursery Inc.
(Mason, MI) except for Potentilla anserina, which was planted from
stolons supplied by Hortech, Inc. There were 27 plugs of each native taxa
included in the study. All plugs and seed were planted or sown on the platforms
15 June 2001. An automated overhead irrigation system (Rainbird; Azusa, CA) was
utilized to support seed germination, plant establishment, and plant coverage.
Plants were evaluated over three years (2001-2004) for
growth, survival during establishment and overwintering, and visual appearance.
During the first season, growth of most native plants peaked in September, and
then declined with the onset of dormancy. Optimum growth and appearance during
the entire first season was possible because irrigation was provided during the
plant establishment phase. Supplemental irrigation was much reduced during the
second season and was terminated completely by 10 July of the second season.
Therefore, after this date plants had to rely on natural rainfall, the likely
scenario on most extensive green roofs. The termination of supplemental
irrigation was fatal to many of the native taxa. At the end of the 2002 growing
season, there were no surviving plants of A. foeniculum, A. laevis, F.
virginiana, L. spicata, M. fistulosa, M. punctata, P. purpureum, P. anserina, R.
hirta, S, scoparium, and S. rigida. Likewise, there were high
mortality rates for C. lanceolata, J. effusus, K. macrantha, and S.
heterolepis. Allium cernuum, O. humifusa, T. ohiensis, but all of
the Sedum proved to be drought tolerant.
Ideal plant selections for extensive green roofs in
northern climates such as Michigan that lack irrigation must be heat and cold
tolerant, drought resistant, have a high growth index in order to provide quick
coverage, and must be self-generating by seed, root systems, or some other
means. When the study was terminated in 2004, of the species tested, all nine
species of Sedum along with A. cernuum, C. lanceolata, and T.
ohiensis were the most suitable for unirrigated roofs. Although, Opuntia
humifusa survived, it lacked the ability to provide quick surface coverage.
If irrigation is available, then other native species are potential selections.
No significant differences were found among the commercial drainage systems.
Complete results are published in Monterusso et al. (2005)
A camera stand was
built for taking digital photographs from above the platforms. Images
are analyzed with SigmaScan Pro software to provide a quantitative
assessment of initial plant growth and coverage.
A point frame
transect is used to measure plant competition over time.
Table 1. Representative growth (coverage) at three substrate depths
(2.5, 5.0, and 7.5 cm) over three years.
15 July 2003
1 July 2005
7 July 2006
In both experiments, species are being evaluated at the
three substrate depths for such characteristics as propagation success, rate of
establishment, growth and survival, groundcover density, ability to exclude
invasive weeds, competition among species, persistence over several years,
tolerance to low winter temperatures, and drought resistance. Rate of
establishment and initial plant growth are being determined by utilizing
SigmaScan Pro 5.0 image analysis software (SPSS Science, Chicago, Ill.). A
camera stand was constructed to suspend a digital camera equipped with a 0.8X
wide conversion lens approximately 163 cm (5’4”) above the platforms. These
pictures are taken weekly until the plants enter dormancy in late fall and then
picture taking is resumed the following Spring. The SigmaScan program analyzes
these digital photographs to determine the percentage of plant canopy that can
be attributed to each individual species.
After initial growth rates are established and plants
begin to fill in the platforms, a point-frame is utilized to measure community
composition and change over time. The point-frame is a stainless steal frame
with ten strings spread horizontally and vertically to create a fish line grid.
At each of the 100 intersection points, leaf area index is measured by recording
all species that come in contact with a vertical needle. Every species that
intersects is recorded based on their origin in the canopy layer. It is
essential to determine the tendency of neighboring plantings to displace and
possibly eradicate adjacent species. Susceptibility to plant competition will be
important to predict the long-term stability of the planted communities as well
as preservation of the aesthetic goals of the roof design. Equally critical is
determination of the resilience and seasonal fluctuation of each of the selected
species over the growth season and after winter dormancy. Therefore, the
platform installations in these studies must be evaluated over the course of
several seasons for overwintering plant survival, recovery, and plant community
Initial results are published in Durhman et al. (2007)
Effect of planting season on establishment. The
objective of was to quantify the effect of substrate depth and planting season
on successful establishment of plugs of Sedum species on green roofs. Plugs of
nine species of Sedum were planted at depths of 4.0, 7.0, and 10.0 cm on green
roof platforms in autumn (September 20, 2004) and spring (June 8, 2005) and then
evaluated for survival on June 1, 2005 and June 1, 2006 respectively. Overall,
spring planting exhibited superior survival rates (81%) compared to autumn (23%)
across substrate depths. Sedum cauticola ‘Lidakense’, S. floriferum, and S.
sexangulare were not affected by season of planting. Sedum cauticola barely
survived at any substrate depth or planting season, whereas the latter two
exhibited nearly 100% survival regardless of planting season. All other species
had superior survival percentages when planted during spring.
Complete results are published in Getter and Rowe (2007)
J. Environ. Hort 25(2):95-99.
Greenhouse evaluation of succulents.
kamtshaticum can live for at
least 88 days without water.
Greenhouse studies on drought tolerance. The
first greenhouse study consisted of seven species combinations subjected to five
different watering regimes. Species included individual trays of a native
perennial (Coreopsis lanceolata); a native grass (Schizachyrium
scoparium); Sedum album; Sedum reflexum; Sedum
kamtschaticum; a mixture of seven sedum species; and a control with no
plants. Coreopsis lanceolata and S. scoparium were chosen to
include a native forb and grass. These species were two of the most drought
tolerant plants of the 18 Michigan native species that we have tested on roof
platforms over the past two years. Sedum album, S. reflexum, and
S. kamtschaticum were chosen because they possess small, medium, and
large sized leaves, respectively, traits that may influence evapotranspiration.
Irrigation regimes consisted of watering every other day, once a week, once
every two weeks, once every four weeks, and never. Each treatment was replicated
eight times for a total of 280 trays arranged in a completely random design.
The second greenhouse study consisted of two
species combinations (a mixture of seven sedum species and a control as
described above), three substrate depths, and five watering regimes (same as
above). The three substrate depths included 2.5 cm of media with 1 cm of water
retention fabric, 2.5 cm of media with 2 cm of fabric, and 5 cm of media with 1
cm of fabric. Each treatment was replicated eight times for a total of 240 trays
arranged in a completely random design. All trays in both studies included the
XeroFlor green roof drainage system and substrate carrier (Behrens
Systementwicklung, Groß Ippener, Germany). The growing substrate was composed of
expanded slate, USGA specification sand; peat, and aged compost.
During both greenhouse studies, evapotranspiration was
measured by obtaining tray weights. Initially tray weights were obtained daily
and thereafter on a periodic basis. Substrate moisture content was recorded with
a Theta Probe Soil Moisture Sensor ML2X (Delta-T Devices, Ltd., Cambridge,
U.K.). In addition, plant stress was monitored with chlorophyll fluorescence (Fv/Fm)
measurements taken on randomly selected leaves with a Plant Efficiency Analyzer
(PEA) fluorometer (Hansatech Instruments Ltd., Norfolk, England, UK). Since
chlorophyll fluorescence levels are tied to the maximum dark-adapted
photochemical efficiency of photosystem II (PSII), they can serve as a general
measurement of plant photosynthetic potential. At the conclusion of each
experiment, dry mass accumulation was calculated from shoot and root dry
Results of the first study indicate that even after the
four-month period, Sedum spp. survived and maintained active
photosynthetic metabolism, relative to
and Coreopsis. Furthermore,
when Sedum was watered after 28 days of drought, chlorophyll fluorescence
(Fv/Fm) values recovered to values
characteristic of the 2 days between watering (DBW) treatment. In contrast,
the non-CAM plants required watering frequency every other day in order to
survive and maintain active growth and development. Regardless of species, the
greatest increase in total biomass accumulation and fastest growth occurred
under the 2 DBW regimes.
In the second study, substrate volumetric moisture content
could be reduced to 0 m3 • m-3 within one day after
watering depending on substrate depth and composition. Deeper substrates
provided additional growth with sufficient water, but also required additional
irrigation because of the higher evapotranspiration rates resulting from the
greater biomass. Over the 88 day study, water was required at least once every
14 days to support growth in green roof substrates with a 2 cm media depth.
However, substrates with a 6 cm media depth could do so with a watering only
once every 28 days. Although vegetation was still viable after 88 days of
drought, water should be applied at least once every 28 days for typical green
roof substrates and more frequently for shallower substrates to sustain growth.
The ability of Sedum to withstand extended drought conditions makes it
ideal for shallow green roof systems.
Complete results are published in VanWoert et al. (2005)
HortScience 40(3):659-664 and Durhman et al. (2006) HortScience 41(7):1623-1628.
Substrate composition and fertility.
the green roof industry, there is a need to define growing substrates that are
lightweight, permanent, and can sustain plant health without leaching nutrients
that may harm the environment. High levels of substrate organic matter is not
recommended because it will decompose resulting in substrate shrinkage and can
leach nutrients such as nitrogen (N) and phosphorus (P) in the runoff. The same
runoff problems can occur when fertilizer is applied. Also, in the midwestern
U.S., there is a great deal of interest in utilizing native species and
recreating natural prairies on rooftops. Since most of these native species are
not succulents, it is not known if they can survive on shallow extensive green
roofs without irrigation.
Five planting substrate compositions containing 60, 70,
80, 90, and 100% of heat-expanded slate (PermaTill; Carolina Stalite; Salisbury,
N.C.) were used to evaluate the establishment, growth, and survival of two
stonecrops (Sedum spp.) and six non-succulent natives to the midwestern
U.S. prairie over a period of 3 years. A second study evaluated these same
plant types that were supplied with four levels of controlled-release
fertilizer. Both studies were conducted in interlocking modular units (36 x 36
inches) designed for green roof applications containing 10 cm of substrate.
Higher levels of heat-expanded slate in the substrate
generally resulted in slightly less growth and lower visual ratings across all
species. By May 2004, all plants of smooth aster (Aster laevis),
horsemint (Monarda punctata), black-eyed susan (Rudbeckia hirta),
and showy goldenrod (Solidago speciosa) were dead. To a lesser degree,
half of the lanceleaf coreopsis (Coreopsis lanceolata) survived in 60 and
70% heat-expanded slate, but only a third of the plants survived in 80, 90, or
100%. Regardless of substrate composition, both ‘Diffusum’ stonecrop (Sedum
middendorffianum ‘Diffusum’) and ‘Royal Pink’ stonecrop (Sedum spurium
‘Royal Pink’) achieved 100% coverage by June 2002 and maintained this
coverage into 2004. In the fertility study, plants that received low fertilizer
rates generally produced the least amount of growth. However, water availability
was a key factor. A greater number of smooth aster, junegrass (Koeleria
macrantha), and showy goldenrod survived when they were not fertilized.
Presumably, these plants could survive drought conditions for a longer period of
time since they had less biomass to maintain. However, by the end of three
growing seasons, all three non-succulent natives also were dead.
Overall results suggest that a moderately high level of
heat-expanded slate (approximately 80%) and a relatively low level of
controlled-release fertilizer (50 g×m-2
per year) and can be utilized for green roof applications when growing
succulents such as stonecrop. However, the non-succulents used in this study
require deeper substrates, additional organic matter, or supplemental
irrigation. By reducing the amount of organic matter in the substrate and by
applying the minimal amount of fertilizer to maintain plant health, potential
contaminated discharge of N, P, and other nutrients from green roofs is likely
to be reduced considerably while still maintaining plant health.
Complete results are published in Rowe et al. (2006)
Carbon sequestration potential. According
to the Intergovernmental Panel on Climate Change, carbon dioxide (CO2)
concentrations in the atmosphere have increased 32% since 1750. Moreover, the
IPCC states that human activity is the cause of such increases, primarily
through the burning of fossil fuels which release CO2. Because CO2 is one of
the atmospheric gases that reduce the amount of outgoing terrestrial energy from
escaping into space, increased levels of this gas will ultimately lead to an
increase in the earth’s temperatures. Many scientists are seeking methods to
remove atmospheric carbon and store it elsewhere in a stable state, thereby
offsetting the human addition of carbon to the atmosphere. Using plants to do
this is referred to as terrestrial carbon sequestration. Through the process of
photosynthesis, carbon dioxide is removed from the atmosphere and stored as
carbon in biomass. If net primary production of these ecosystems exceeds
decomposition, then these systems become at the very least a short term sink for
The objective of this study is to quantify the carbon
storage potential of extensive green roofs and to evaluate the effect that
species has on carbon flux. To accomplish this research objective, a study was
initiated on the roof of the Plant and Soil Sciences Building in April 2007.
The study area measures 2.84 m x 4.6 m with 20 plots, each measuring 0.71 m x
0.92 m. Each plot is covered with a single species of Sedum (S. acre, S. album,
S. kamtshaticum var ellacombianum, or S. spurium ‘Summer Glory’) germinated from
seed or a ‘substrate only’ treatment. Each row is blocked, with four replicates
and five treatments at a depth of 6.0 cm (2.5 in). Carbon analysis will be
performed by sampling aboveground biomass, below ground biomass (roots), and
soil carbon content. Sampling will occur periodically over the course of
View of tipping
buckets used to measure the volume and rate of runoff from roof
differences in runoff at various substrate depths and roof slopes.
Stormwater management on roof platforms. Two studies were recently
completed that quantified the differences in water retention among (1) roof
vegetation types and (2) among combinations of green roof slopes and substrate
depths. Fifteen simulated roof platforms (ChristenDetroit, Detroit, Mich.) with
overall dimensions of 2.44 m x 2.44 m (8 ft x 8 ft) were utilized at the
Michigan State University Horticulture Teaching and Research Center (East
Lansing, Mich.). Each platform simulated an actual commercial extensive green
roof and included an insulation layer, protective layers, and waterproofing
membrane. Three of the platforms were divided into three sections measuring 0.67
m x 2.44 m (2.2 ft x 8 ft) and were used for the vegetation study. The other
twelve platforms were utilized for the slope/depth study. Aluminum sheet metal
troughs were attached on the low end of the platforms to capture stormwater
exiting the platform. For the vegetation type study the troughs are divided into
three separate sections corresponding to the three divided sections. For the
vegetation type study, platforms were set at a 2% slope with the top edge of the
high end 0.9 m (3.0 ft) above ground level. Platforms used in the slope/depth
study were placed at 2% or 6.5% slope. All platforms were oriented with the low
end of the slope facing south to maximize sun exposure.
All platforms except for one of the three self-contained
sections on each of the platforms utilized for the vegetation type study
contained XeroFlor drainage layers, water retention fabric, and substrate
carriers. The growing substrate consisted of heat-expanded slate (PermaTill®,
Carolina Stalite Company, Salisbury, N.C.), USGA (United States Golf
Association) grade sand, Michigan Peat, 5% Dolomite, composted yard waste, and
composted turkey litter. For the vegetation type study, each platform section
with the XeroFlor drainage system installed received planting substrate to a
depth of 2.5 cm (1.0 in). The twelve platforms utilized in the slope/depth study
received 2.5, 4.0, or 6.0 cm (1.0, 1.6, or 2.4 in) of substrate on top of the
substrate carrier. The four treatments were a 2% slope with either 2.5 or 4.0 cm
of substrate and the 6.5% slope with 4.0 or 6.0 cm of substrate.
Three roof types were tested in the roof vegetation type
study: an extensive green roof with vegetation, an extensive green roof with
substrate only, and a conventional commercial roof with a 2 cm (0.8 in) deep
gravel ballast. Treatments were arranged in a randomized complete block design
with each platform corresponding to one block. Vegetation, substrate only, or
gravel ballast were randomly assigned within sections of each platform. For the
slope/depth study, all platforms were covered with vegetation. For both studies,
100% coverage was achieved on the vegetated section prior to the initiation of
data collection. Taxa included several species of Sedum planted from seed
(Jelitto Staudensamen, GmbH, Schwarmstedt, Germany) at a rate of 1.3 g•m-2
(0.004 oz•ft-2) for each species.
Model TE525WS tipping bucket rain gauges (Campbell
Scientific, Inc., Logan, Utah) were mounted under the drain of each platform
section to quantify stormwater runoff. An additional tipping bucket was mounted
in each gravel section to record actual rainfall on the vegetation type
platforms. Also, a Campbell Scientific’s CM6 tripod weather station was
installed on the research site to aid in determining meteorological variables.
The weather station included a temperature and relative humidity probe covered
by a 6-plate gill radiation shield. In addition, instruments to measure wind
speed and direction were installed as well as a pyranometer. Data from the
tipping bucket rain gauges and tripod weather station were collected every five
minutes, 24 hours a day using a Campbell Scientific CR10X datalogger with
peripheral multiplexers, switch closure modules, and storage module. A rainfall
event was defined by two rainfalls separated by a period of six hours or more,
with an easily distinguishable flow hydrograph.
Over the 14-month period the study was conducted, the
vegetated roof treatments retained 60.6% of rainfall from 83 measured rain
compared to 50.4% and 27.2% for the media-only and conventional gravel ballast
roofs, respectively. In the slope/depth study, platforms at 2% slope with a 4
cm media depth had the greatest mean retention, although the difference from the
other treatments was minimal. The combination of reduced slope and deeper
media clearly reduced the total quantity of runoff. For both studies, vegetated
green roof systems not only reduced the amount of stormwater runoff, they also
extended its duration over a period of time beyond the actual rain event.
Complete results are published in VanWoert et al. (2005)
Journal of Environmental Quality 34(3):1036-1044.
A third stormwater runoff study was initiated in May 2005
to quantify the effect that roof slope has on green roof stormwater retention.
Runoff was analyzed from twelve extensive green roof platforms constructed at
four slopes (2%, 7%, 15%, and 25%). Rain events were categorized as light (<2.0
mm) (0.08 in), medium (2.0 – 10.0 mm) (0.08 in – 0.39 in), or heavy (>10.0 mm)
(>0.39 in). Data demonstrated an average retention value of 80.8%. Mean
retention was least at the 25% slope (76.4%) and greatest at the 2% slope
(85.6%). In addition, runoff that did occur was delayed and distributed over a
long period of time for all slopes. Curve numbers, a common method used by
engineers to estimate stormwater runoff for an area, ranged from 84 to 90, and
are all lower than a conventional roof curve number of 98, indicating that these
greened slopes reduced runoff compared to traditional roofs.
Roof over the
headhouse of the Plant and Soil Sciences Building prior to installation
of green roof in May 2004.
The roof is
instrumented with heat flux sensors, thermocouples, and soil moisture
probes at various locations inside the building and in the roof profile.
Green roof on Plant
and Soil Sciences Building (May 2006).
flowering on Plant and Soil Sciences Building (July 2006).
Monitoring of Green Roof on Plant & Soil Science
Building. An extensive green roof was installed in May 2004 on a
portion of the roof (3500 square feet) over the headhouse of the Plant & Soil
Sciences Building. The green portion covers the natural drain field around the
center drain, whereas, the drain field surrounding the southern drain remains as
a conventional roof. Thus, we have two experimental roof sections where we can
obtain quantifiable data comparing heat flux, roof membrane temperatures, and
stormwater issues. In addition, new plant species will be tested, the site will
be used to raise public awareness, and the project will help promote MSU’s
efforts as a sustainable campus.
On the green portion of the roof, thermocouples are located
inside of the building; on top of the roof membrane, insulation layer, and water
retention fabric; under the plant canopy on the growing substrate surface, and
at a height of one meter above the foliage. Heat flow sensors are placed above
the insulation layer and soil moisture probes have been installed in the
moisture retention fabric and in the growing substrate. On the conventional
portion of the roof, thermocouples are located inside the building, on top of
the roof membrane, above the insulation layer, on top of the gravel ballast, and
one meter above the roof surface. Heat flow and moisture sensors are also
present on the conventional side. Sensors are replicated three times at separate
locations in the ballasted and vegetated roof sections for a total of 36
thermocouples, 6 heat flow sensors, and 9 moisture probes. Ambient temperature,
irradiance levels, wind velocity, relative humidity, and precipitation are
continuously recorded by a weather station located on the roof. Data is recorded
every five minutes, 24 hours a day using a Campbell Scientific CR10X datalogger
with peripheral multiplexers, switch closure modules, and storage module.
Research plots on
the Communication Arts Building are comparing plant responses at various
substrate depths in full sun and shade.
Plant evaluations on the Communications Arts
Building. Small green roof research plots (400 square feet) were
installed on the Communication Arts Building in May 2005. One factor being
studied is the effect of irradiation levels on plant community development.
Because of the design of the building, we can compare a plot that is always in
full sun to another that is continuously in the shade. One experiment compares
irradiance levels on a typical green roof sedum mix of Sedum acre, Sedum
album, Sedum kamschaticum, Sedum reflexum, and Sedum spurium in 10 cm
(4 in) of media. As second study consists of North American native species Allium cernuum, Carex flacca, Sedum stenopetalum, Sedum divergens, Sedum
urvillei, Talinum calycinum, and Talinum parviflorum, as well as Sedum ‘Coral Carpet’ and
Sedum acre ‘Oktoberfest’ growing in the sun
or shade in 8 or 12 cm (3 or 5 in) of media.
The plots are instrumented with soil moisture sensors,
thermocouples, pyranometers to measure irradiance levels, and a weather station
to measure wind speed, ambient air temperatures, and rainfall. A data logger
powered by solar energy records data continuously.
The Ford Motor Company assembly plant in Dearborn, Michigan. The green
roof covers 10.4 acres.
An extensive green roof native plant community on the convention center
of the Church of Jesus Christ of Latter-day Saints in Salt Lake City,
Future of Green Roofs in
the United States
In Germany, it is estimated 12% of all flat-roofed
buildings are covered with vegetation, a number that is increasing as the German
green roof industry continues to grow 10 to 15% per year. In Michigan and the
rest of North America the concept of green roofs is just now being introduced. A
few installations exist on this continent, the largest extensive roof (10.4
acres) being the new assembly plant at the Rouge facility of Ford Motor Co. in
Will green roofs ever catch on in the United States like
they have in Europe? Several barriers to widespread acceptance exist such as a
lack of awareness regarding green roofs, potentially higher installation costs,
limited quantifiable data pertaining to the benefits they provide, no technical
information on how to build them, and a lack of government incentives or tax
breaks. However, all of these problems are currently being addressed. These
barriers are not insurmountable, as the same barriers have been overcome in
Germany. In the U.S. the concept of green roofs is just now being introduced and
will likely become more common in the future. They represent an entirely new
market for landscape designers/architects, nursery operations, and landscape
contractors; and the potential market includes all existing and future roofs in
Graduate Students in MSU Green Roof Research Program
Michael Monterusso (MS, Spring 2003)
Horticulture Manager, Daniel Stowe Botanical Garden, Belmont, NC
Nicholaus VanWoert (MS 2004)
Resource Analyst, Michigan Department of Transportation, Kalamazoo, MI
Angela Durhman (MS 2005)
Green Roof Specialist, Tecta America Corp and Magco, Inc. Jessup, MD.
Kristin Getter (MS 2006)
Currently PhD student at MSU
Publications From MSU Research Program
To obtain pdf files of the peer-reviewed scientific articles,
please send requests to Brad Rowe at email@example.com.
Articles in peer reviewed scientific
Getter, K.L., D.B.Rowe, G.P. Robertson, B.M. Cregg, and
J.A.Andresen. 2009. Carbon sequestration potential of
extensive green roofs. Environmental Science and Technology
Getter, K.L., D.B.Rowe, and B.M. Cregg. 2009. Solar radiation
intensity influences extensive green roof plant communities.
Urban Forestry and Urban Greening 8(4):269-281.
Getter, K.L. and D.B.Rowe. 2009. Substrate depth influences sedum plant
community on a green roof. HortScience 44(2):401-407.
Getter, K.L. and D.B. Rowe. 2008. Media depth influences Sedum green
roof establishment. Urban Ecosystems 11:361-372.
Getter, K.L., D.B. Rowe, and J.A. Andresen. 2007. Quantifying
the effect of slope on extensive green roof stormwater
retention. Ecological Engineering 31:225-231.
Durhman, A.K., D.B. Rowe, and C.L. Rugh.
2007. Effect of substrate depth on initial growth, coverage, and survival of 25
succulent green roof plant taxa. HortScience 42(3):588-595.
Getter, K.L. and D.B. Rowe. 2007. Effect
of substrate depth and planting season on Sedum plug establishment for green
roofs. J. Environ. Hort 25(2):95-99.
Oberndorfer, E., J. Lundholm, B.
Bass, M. Connelly, R. Coffman, H. Doshi, N. Dunnett, S. Gaffin, M.
Köhler, K. Lui, and B. Rowe. 2007. Green roofs as urban
ecosystems: ecological structures, functions, and services. BioScience
Durhman, A.K., D.B. Rowe, and C.L. Rugh.
2006. Effect of watering regimen on chlorophyll fluorescence and growth of
selected green roof plant taxa. HortScience 41(7):1623-1628.
Getter, K.L. and D.B. Rowe.
2006. The role of green roofs in sustainable development. Hort Science
Rowe, D.B., M.A. Monterusso,
and C.L. Rugh. 2006. Assessment of heat-expanded slate and fertility
requirements in green roof substrates. HortTechnology 16(3):471-477.
Monterusso, M.A., D.B. Rowe,
and C.L. Rugh. 2005. Establishment and persistence of Sedum spp. and
native taxa for green roof applications. HortScience 40(2):391-396.
VanWoert, N.D, D.B. Rowe,
J.A. Andresen, C.L. Rugh, R.T. Fernandez, and L. Xiao. 2005. Green roof
stormwater retention: Effects of roof surface, slope, and media depth. J.
Environ. Quality 34(3):1036-1044.
VanWoert, N.D, D.B. Rowe,
J.A. Andresen, C.L. Rugh, and L. Xiao. 2005. Watering regime and green roof
substrate design affect Sedum plant growth. HortScience 40(3):659-664.
Getter, K.L. and
D.B. Rowe. 2008. Selecting plants for extensive green roofs in the
U.S. Extension Bulletin E-3047, Michigan State University.
Papers from proceedings of professional
Getter, K.L. and D.B.Rowe. 2009. Carbon
sequestration potential of extensive green roofs. Proc. of 7th North
American Green Roof Conference: Greening Rooftops for Sustainable
Communities, Atlanta, GA. 3-5 June 2009. The Cardinal Group, Toronto.
Getter, K.L. and D.B. Rowe. 2008. Carbon sequestration potential of
extensive green roofs. Proc. of World Green Roof Conference, London,
U.K. 17-18 Sept, 2008.
Getter, K.L. and D.B. Rowe. 2008. Effect of solar radiation levels on
native and non-native species. Proc. of 6th North American Green Roof
Conference: Greening Rooftops for Sustainable Communities, Baltimore,
MD. 30 April -2 May, 2008. The Cardinal Group, Toronto.
Getter, K.L. and D.B.
Rowe. 2007. Effect of substrate depth and planting season on Sedum plug
establishment for extensive green roofs. Proc. of 5th North American Green Roof
Conference: Greening Rooftops for Sustainable Communities, Minneapolis, MN. 29
April -2 May, 2007. The Cardinal Group, Toronto
Rowe, D.B., C.L. Rugh, and
A.K. Durhman. 2006. Assessment of of substrate depth and composition on green
roof plant performance. Proceedings of 4th North American Green Roof Conference:
Greening Rooftops for Sustainable Communities, Boston, MA. 10-12 May, 2006.
The Cardinal Group.
Rowe, D.B., M.A. Monterusso,
and C.L. Rugh. 2005. Evaluation of Sedum spp. and Michigan native taxa
for green roof applications. p. 469-481. In Proceedings of 3rd North
American Green Roof Conference: Greening Rooftops for Sustainable Communities,
Washington, DC. 4-6 May 2005. The Cardinal Group, Toronto.
Durhman, A., N.D. VanWoert,
D.B. Rowe, C.L. Rugh, and D. Ebert-May. 2004. Evaluation of Crassulacean species
on extensive green roofs. p. 504-517. In Proc.
of 2nd North American Green Roof Conference: Greening Rooftops for
Sustainable Communities, Portland, OR. 2-4 June 2004. The Cardinal Group,
Monterusso, M.A., D.B. Rowe,
C.L. Rugh, and D.K. Russell. 2004. Runoff water quantity and quality from green
roof systems. Acta Hort 639:369-376.
Rowe, D.B. and C.L. Rugh.
2003. The green roof research program at Michigan State University. Proceedings
International Plant Propagators Society 53:104-106.
Rowe, D.B. 2003. Green
roofs – A new market. Proceedings Southern Nursery Assoc. Research Conf.
Rowe, D.B., C.L. Rugh, N.
VanWoert, M.A. Monterusso, and D.K. Russell. 2003. Green roof slope, substrate
depth, and vegetation influence runoff. p. 354-362. In Proceedings of 1st
North American Green Roof Conference: Greening Rooftops for Sustainable
Communities, Chicago. 29-30 May 2003. The Cardinal Group, Toronto.
Rowe, D.B., C.L. Rugh, and
D.K. Russell. 2002. Green roof installation at Ford Motor Company. Proceedings
International Plant Propagators Society 52:127-130.
The following companies or professional organizations have contributed direct
support or in-kind support to our research program:
American Hydrotech, Chicago, IL (www.hydrotechusa.com)
Behrens Systementwicklung, Groß
Richard Brown, Meridian Township Community Planning and Development
Carolina Stalite, Salisbury, NC (www.permatill.com)
ChristenDETROIT Roofing Contractors, Detroit, MI
Green Roof Plants, Street, MD (www.greenroofplants.com)
Green Roofs for Healthy Cities, Toronto (www.greenroofs.org)
Ford Motor Company, Dearborn,
Hortech, Inc., Spring Lake, MI
Intrinsic Perennial Gardens, Hebron, IL (www.intrinsicperennialgardens.com)
LiveRoof, LLC, Spring Lake, MI
McDonough Braungart Design Chemistry, Charlottesville, VA (www.mbdc.com)
Michigan Agricultural Experiment Station (www.maes.org)
Michigan Department of Agriculture
Michigan Nursery and Landscape Association (www.mnla.org)
MSU Office of Vice President of Finance and Operations
MSU Office of Vice President of Graduate Research
Osburn Industries, Taylor, MI
Ray Stephenson, International Sedum Society, Northumberland, United Kingdom
Renewed Earth, Kalamazoo, MI (www.renewedearth.com)
Sarnafil, Inc., Canton, MA (www.sarnafilus.com)
Siplast, Inc., Irving, TX (www.siplast.com)
University of Georgia, Athens, GA
Walters Gardens, Zeeland, MI (www.waltersgardens.com)
Wildtype Nursery, Mason, MI (www.wildtypeplants.com)
Xeroflor America, Durham, NC. (www.xeroflora.com)
Useful Green Roof Links
Earth Pledge (www.earthpledge.org)
Photos of Green Roofs
Green Roofs for Healthy Cities (www.greenroofs.org)
U.S. Green Building Council Leadership in Energy & Environmental Design (www.usgbc.org/LEED/LEED_main.asp)
Penn State University
North Carolina State University
Southern Illinois University, Edwardsville, Green Roof Environmental Evaluation
William McDonough & Partners
Sustainable Design Web Resources (www.fpm.wisc.edu/campusecology/Docs/Sust%20Web%20Resources.htm)
Green Building Products
by McGraw-Hill Sweets
View of an extensive green roof on the assembly plant at Ford Motor
Company in Dearborn, Michigan (June 2003).
Ford assembly plant (July 2003).
Aerial view of Chicago City Hall. The building is eleven stories tall,
220 feet above street level, and covers 38,000 square feet. (Photo
courtesy of Roofscapes, Inc.).
An intensive green roof on a restaurant in Lansing, Michigan.
Sedum cover the Schipol International Airport in Amsterdam.
A meadow-like roof on a commercial building in Kassel, Germany.
The convention center of the Church of Jesus Christ of Latter-day Saints
in Salt Lake City, Utah.
Garden shed at Quail Botanic Garden near San Diego, California.
Rowe doghouse for Finnegan and Cooper in Mason, Michigan (August 2003).
Rowe doghouse (July 2006).
in bloom on doghouse (July 2004).
in flower on doghouse (July 2005).