Leading by Example at the Munro Coast Guard Building Complex in Washington D.C.

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Green roofs, rain gardens, and constructed wetlands treat all the stormwater at the Munro building complex. The overall effect of this integrated design approach means there is no runoff from this site! Plants of the constructed wetland utilize residual nutrients from runoff before water is returned to a retention pond. Photo: Bruce Dvorak

Introduction

Green roofs reduce localized flooding, conserve energy in buildings, mitigate urban heat islands, sequester carbon, create habitats for wildlife, support healing environments for people, reduce operating expenses, and so much more. So why aren’t green roofs more widely adopted? In efforts to demonstrate how the innovation of green roofs can benefit public infrastructure, the U.S. General Services Administration and the Department of Homeland Security implemented 12 acres of green roofs at the Douglas A. Munro Coast Guard Headquarters in Washington D.C. In this article, I share three insights about how plants help make the innovation of green roofs an invaluable resource for public infrastructure.

Worldwide, the innovation of green roofs has been supported by legislation and incentives for green roofs on public and private rooftops. Germany, France, Japan, Singapore, and other countries have implemented legislation to require green roofs for specific applications (Savarani 2019). Toronto, London, Denver, New York, Austin, San Francisco and Portland, Oregon require or offer financial support for the development of green roofs on some buildings (Savarani 2019). The U.S. General Services Administration (GSA) and the U.S. Environmental Protection Agency (EPA) offer guidance and support for developers to implement green roofs for mitigating stormwater runoff and managing urban heat islands. They also collaborated to make a demonstration of how the innovation of green roofs can be used on public infrastructure.

One of the best ways to promote a new technology, especially one that can have a higher cost upfront than a conventional approach is through pilot or demonstration projects. In Washington, D.C. the General Services Administration has implemented dozens of green roofs in the Washington D.C. area, including one of the largest in North America (557,000 ft² or 51,747 m²), at the Douglas A. Munro Coast Guard Headquarters buildings at the St. Elizabeth’s West Campus. The GSA considers green roofs to be a viable and reliable asset. Here is why the GSA believes in green roofs:

“Green roofs reduce polluted stormwater that runs into local bodies of water; lessen energy use and costs in the buildings they top off; and reduce urban heat islands, or pockets of concrete and asphalt that absorb heat and radiation from the sun. They can support energy producing solar panels that are more efficient when cooled by the green roof ecosystem. Other advantages include extending the longevity of the roof and aesthetics (General Services Administration 2023).”

Aside from high aspirations for sustainability, a return on the financial investment of green roofs was a high priority. In their report on green roof costs and benefits, the GSA studied green roofs and found that the estimated payback period for a simple extensive green roof was about 6.2 years nationally, with a return on investment (ROI) of about 224% for a 10,000 sq. ft roof. This means that many of the most important new public buildings constructed in the Washington D.C. metro region are now covered with green roofs and are saving taxpayers dollars for many decades to come (General Services Administration 2011, General Services Administration 2013).

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A Case for Green Roofs at the Douglas A. Munro Coast Guard Headquarters Facilities

It is worthwhile to periodically review how buildings with green roofs implemented as a public investment are faring over time. In October of this year, I had the opportunity to tour the Douglas A. Munro Coast Guard Headquarters campus during the ASLA National Conference in Washington D.C. Some of the first green roofs were installed at the Munro building complex in 2013. After nearly a decade since the green roofs were installed, there is much to learn from this massive and innovative project. This article reports on three planting innovations for green roofs on public buildings.

*Native prairie plants compete for sunlight in a woodland opening at the* *Mt. Cuba* Center in Delaware, near Washington D.C. Micro-prairies such as these once flourished across the Piedmont Plains along the East Coast. Plants native to prairies and meadows deliver the greatest range of ecological benefits on green roofs. Photo: Bruce Dvorak

1. Native Plants Can be Maintained on Public Green Roofs

Sedum-based green roofs tend to dominate public buildings, including Washington D.C (Scholz-Barth and Tanner 2004). While these simple green roofs deliver environmental benefits, green roofs with greater plant diversity offer greater ecosystem benefits and resilience, especially when populated with plants native to the ecoregion (Dvorak and Bousselot 2021).

In many highly developed parts of the world, the native plant communities have been greatly reduced or may not be well-known. While prairies are known to have once dominated central portions of North America, they also were widespread along the East Coast throughout the Piedmont region. Compared to prairies of the Midwest, piedmont prairies were smaller in size. They were distributed in isolated locations where gravel soil persisted and were often associated with wooded habitats such as oak openings and oak or pine savannas. Nonetheless, there are a few examples of green roofs on public buildings with plants native to the piedmont prairies.

In efforts to help meet its high standard for sustainability, the GSA hired a diverse team to visualize a sustainable and integrated campus master plan. The result was 29 green roofs on an array of buildings, to meet goals for its LEED Gold certification. The re-visioning of the St. Elizabeth’s West campus to adapt to its new use as a consolidated headquarters for the Department of Homeland Security U.S. Coast Guard included a mix of new and revitalized buildings, with phase 1, the Douglas A. Munro Coast Guard Headquarters, now planted with about 12 acres (4.8 hectares) of green roofs, including several large meadow-based green roofs composed of native grasses, wildflowers, and small shrubs.

One of several semi-intensive meadow-based green roofs at the Munro building complex. This green roof was planted with native grasses and wildflowers that can tolerate dry or wet conditions. Photo Bruce Dvorak

Vegetation throughout the site was selected not just for its ornamental characteristics, but also to perform ecosystem services such as managing stormwater onsite, conserving energy inside the buildings, providing beautiful views and supporting biodiversity on rooftops (McKee 2015). The design team needed vegetation that could tolerate dry or wet environments, and the selected plants needed to be native to the mid-Atlantic region from a range of moisture gradients. This includes plants native to drier sunny and sloped habitats of the highlands of the Blue Ridge mountains and moisture-loving plants from the tidal marshes of the coastal region to perform cleaning and infiltration of runoff.

Although sedum-based extensive green roofs are present throughout the building complex, the semi-intensive meadow-based green roofs are planted at specific locations where green roofs are highly visible, cover large areas, and are accessible for maintenance. This approach places the meadow-based green roofs on rooftops where they will be most appreciated from the inside and provide the most environmental and economic benefits. The 6-18 inch depth of substrate allows meadow/prairie vegetation to be used, because these plants have deep root systems. Four different providers of growing media were used to assemble and support the green roof vegetation. The following plant taxa were installed on the meadow roofs (McKee 2015):

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Grasses and Grasslike Vegetation Planted on the Munro Green Roofs

Fifteen taxa of grass were installed on the semi-intensive green roofs. These grasses make up the dominant vegetative bulk and provide a physical structure and growth support to the upright growing wildflowers.

Koeleria macrantha (Prairie June grass)

Panicum amarum (Bitter panic grass and ‘Dewey Blue’)

Panicum virgatum (Switchgrass and ‘Heavy Metal’)

Schizachyrium scoparium (Little bluestem)

Schizachyrium scoparium ‘The Blues’

Sporobolus heterolepis (Prairie dropseed)

Uniola paniculata (Sea oats)

Andropogon virginicus var. virginicus

Bouteloua curtipendula (Side oats grama)

Bouteloua dactyloides (Buffalo grass)

Carex pensylvanica (Pennsylvania sedge)

Carex plantaginea (Seersucker sedge)

Carex platyphylla (Silver sedge)

Deschampsia flexuosa (Wavy hairgrass)

Eragrostis spectabilis (Purple lovegrass)

Herbaceous Wildflowers, Succulents, and Groundcovers Planted on the Munro Green Roofs

Twenty-three taxa of native wildflowers and groundcovers were used on the semi-intensive green roofs (McKee 2015). These plants support the native pollinators, contribute to important development and build-up of a healthy substrate and nutrient base for the long-term support of the green roof ecosystem (Sutton 2015).

Oenothera fruticosa (Narrowleaf evening primrose)

Penstemon digitalis (Foxglove beardtongue)

Phemeranthus calycinus (Large flower flameflower)

Sedum pulchellum (Widow’s cross)

Sedum ternatum (Woodland stonecrop)

Silene caroliniana (Wild pink)

Solidago sempervirens (Seaside goldenrod)

Symphyotrichum ericoides (Heath aster and ‘Snow Flurry’)

Symphyotrichum oblongifolium (Aromatic aster and ‘Outdoor Skies’)

Tradescantia ohiensis (Bluejacket)

Waldsteinia fragarioides (Barren strawberry)

Achillea millefolium (Common yarrow)

Allium cernuum (Nodding onion)

Aquilegia canadensis ‘Little Lanterns’

Asclepias syriaca (Common milkweed)

Asclepias tuberosa (Butterfly milkweed)

Asclepias verticillata (Whorled milkweed)

Baptisia tinctoria (Yellow false indigo)

Campanula rotundifolia (Harebell)

Danthonia spicata (Poverty oat grass)

Eupatorium hyssopifolium (Hyssopleaf thoroughwort)

Eurybia divaricata (White wood aster)

Heuchera americana (American alumroot)

Because the buildings step down the hillside, many of the rooftops are visible from inside the building. The combination of sedums and roof meadows provides a dynamic composition of plants blooming throughout the growing season. Because of the plant diversity, the various habitats attract pollinators and other wildlife to the roof. The endurance of this approach for more than a decade demonstrates how green roofs can be designed and maintained to support regional biodiversity on public infrastructure.

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Tall shrubs and trees are planted at grade (background). The soil was graded to gradually meet up to the prairie roof shown in the foreground. Plants native to the piedmont prairies make a “natural garden” through an at-grade transition to a sunny green roof. The low stone wall begins a series of rain gardens that step down a slope that eventually leads to a bioretention basin and constructed wetland. Photo: Bruce Dvorak

2. Ground to Rooftop Connections Expand Usable Space

Yellow blooms of Seaside goldenrod (Solidago sempervirens) brighten this transitional green roof space where a plaza meets up with a shade garden. The intensive green roof shown here transitions to “at-grade” plantings in the background, where trees, shrubs, and groundcovers create an outdoor room. Photo: Bruce Dvorak

Due to the steep slopes of the Munro building site, the architects and landscape architects proposed a solution where the buildings would step down the slope and complement the natural topography of the site. As a result, additional usable outdoor space came about from a blending of ground plane plantings connecting at the soil level with intensive rooftop terraces. The seamless transitions make for some amazing spaces that would not be possible without green roofs. Large trees and rain gardens were planted in the natural grade. The planted rooftops meet up with the natural grade and give the appearance of a seamless transition. With this approach, maintenance crews need to be aware of where the green roofs begin, so that appropriate maintenance tools and methods can be used to protect and maintain the waterproofing systems. This tiered approach to the building and planting also allows for a contiguous rain train where a combination of green roofs, rain gardens, and constructed wetlands treat all of the water falling on the property.

The unique design and layout of the campus, with buildings cascading down the natural slope allows for an integrated composition of people space with green space. The use of rooftops as plaza and planted areas expands the usable area. In addition, the green roofs help achieve a more than 100 percent retention of stormwater compared to the pre-developed site condition.

3. Adaptive Management of Green Roofs is Part of Regular Upkeep and Maintenance

Keeping the green roofs and rain gardens in top shape requires regular maintenance activities. This includes monthly maintenance visits and a sufficient budget for “replanting” when plant materials die back. All gardens and green roofs need maintenance. What may not typically be seen by the public is the periodic replacement of plants. On the day we visited, maintenance crews brought some new vegetation in pots to replant at a few strategic locations.

This brings to light the importance of having a five-year maintenance plan and budget, as a good practice. This approach is used on many green roofs and is required through the Living Architecture Performance Tool and certification system. This should include planned maintenance meetings, secured budgets, and knowledgeable staff to periodically observe green roofs for locations where plants may be struggling to establish, or dieback occurs from extreme climate events. In this case, these green roofs were under the effects of a drought that had not been experienced in this region in about 30 years. These green roofs are not fertilized or regularly irrigated and are still in good condition. Irrigation is applied in isolated treatments on an as-needed basis. This treat-when-necessary approach requires upper management of facilities to secure knowledgeable staff and maintenance crews that can anticipate challenges and make timely decisions for necessary green roof maintenance activities to take place.

Another important factor in the success of this project is the selection and training of green roof maintenance contractors. The GSA secures 5-year maintenance contracts to ensure continuity on the green roofs from year to year and the retainment and overlap of experienced workers. Maintaining a project like this requires that workers know exactly where at-grade planting transitions to green roofs occur, and how to maintain them. Each garden approach requires its own tools and methods to maintain them. The continuation of contracts is an important incentive for GSA and maintenance workers to sustain the green roofs.

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*Left: maintenance crews remove invasive vegetation common to the region on a green roof. Right: new juniper plants are set aside to replant a small section of a roof garden. Photos: Bruce Dvorak*

Summary

An overview of some of the 29 green roofs at the Munro Coast Guard building complex located in Washington D.C.. This project has zero stormwater runoff due to its innovative combination of rain gardens, green roofs and constructed wetlands. Photo: Bruce Dvorak

This is a view of one of several “eco-roof” habitat islands on the Munro green roofs. These micro-habitats are supported with mounded substrates that rise from six to eighteen inches deep (15.4 cm to 45.72 cm). Native grasses and shrubs support a cultivar of the native sumac shrub. Rhus copallina ‘Creel’s Quintet’ (Creel’s Quintet shining sumac) is seen here rising above the flat roof plane as a focal point visible from an adjacent plaza and conference room. Photo Bruce Dvorak

After more than a decade, the continued presence of 12 acres of green roofs at the Munro U.S. Coast Guard Headquarters, validates how the innovation of green roofs can work wonders for public projects. Nearly all of the rooftops of buildings are completely covered with green roofs, and they thrive with regular maintenance by trained and experienced staff. This amazing project demonstrates:

Bouteloua curtipendula (Side oats grama) grows through a sedum mat on a roof garden at the Douglas A. Munro Headquarters campus. A Corten steel screen is placed as a backdrop to feature the ornamental seedheads. Photo Bruce Dvorak

That without any major failures or setbacks, after more than 10 years, these green roofs have already been paid for, because the return on the investment period of six years has passed. Now, only operational costs of green roofs are required. Based on the typical longevity of green roofs, the waterproofing on these buildings should last another 50 to 60 years, minimum.
The unique design and layout of the campus, with buildings cascading down the natural slope, the green roofs help achieve a more than 100 percent retention of stormwater compared to the pre-developed site condition.
Maintenance of the grounds and green roofs includes regular landscape-type activities. However, the low-input design, featuring a mixture of sedums and native vegetation allows for full coverage of the substrate with plants.
The low-input maintenance approach includes limited application of fertilizer and irrigation. Appropriate substrate depths, plant selection, and maintenance regimes work together to make these green roofs successful.
Forty (40) taxa of native plants are used on the green roofs where substrates vary from 6 to 18 inches. Ten (10) taxa of sedum thrive on the extensive green roofs. The design team brought back vegetation that was once common to the region. The staff enjoy seeing the native birds, butterflies, and bees pollinating the gardens.
One of the most important factors in the success of this project is the continued presence of knowledgeable staff that oversee and direct the operations of the green roofs. Every successful green roof has a “champion”, some designated person or team that consistently meets to observe and make decisions.
The building occupants enjoy health benefits from having views of greenery from most of the windows and being able to sit outside to work and have breaks.

Green Roof Biodiversity Courses

To learn about how green roofs can support heat-tolerant plants and biodiversity, see the new Living Architecture Academy Course: Case Studies of Biodiverse Green Roofs, by Bruce Dvorak.

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Bruce Dvorak, FASLA is a Professor at Texas A&M University in the Department of Landscape Architecture and Urban Planning, where he has been conducting green roof and living wall research since 2009. Bruce is a member of the GRHC Research Committee and founded the Southern Plains Living Architecture Center Regional Center of Excellence. Bruce received the GRHC Research Award of Excellence in 2017 and teaches green roofs and living walls in his courses in landscape architecture programs at Texas A&M University. His edited book, Ecoregional Green Roofs: Theory and Application in the Western USA and Canada (2021) provided inspiration and content for this article.

Acknowledgments

I would like to thank Maureen Alonso and Rasma Plato with GSA for their time and effort with tours of the Green Roofs at the Munro Headquarters and Brandon Hartz, ASLA, and Anne Stanley also with GSA, for reviewing this article. Thank you to Steven Peck for an early review of this article. Thank you also to Ed Snodgrass with Emory Knoll Nursery, and George Coombs director at the Mt. Cuba Center for a tour of the native plant gardens.

Project Credits

Green Roof Design Team: Andropogon and HOK

Three Planting Innovations at the Munro Coast Guard Building Complex in Washington D.C.

Introduction

A Case for Green Roofs at the Douglas A. Munro Coast Guard Headquarters Facilities

1. Native Plants Can be Maintained on Public Green Roofs

Grasses and Grasslike Vegetation Planted on the Munro Green Roofs

Herbaceous Wildflowers, Succulents, and Groundcovers Planted on the Munro Green Roofs

2. Ground to Rooftop Connections Expand Usable Space

3. Adaptive Management of Green Roofs is Part of Regular Upkeep and Maintenance

Summary

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