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Research is key

The following universities are performing extensive research on green roofs:

Michigan State University green roof research objectives 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.

North Carolina State University currently has four extensive green roof research sites in North Carolina. NCSU research focuses on stormwater control - quantity and quality

Penn State University green roof research focuses on stormwater runoff, building energy use, building heat flux, water quality, evapotranspiration model development, roof membrane testing, media analysis, and plant performance.

Our Green Roof Trials

To better integrate buildings into the surrounding landscape, green roof species composition could consist of indigenous (native) plants. This not only visually mimics the surrounding environment, but also contributes to local species diversity and creates natural wildlife habitat. In addition to typical green roof benefits, the use of native plants on roofs allows a structure to contribute to the surrounding environment, and respond to it. No longer a separate entity, a building can truly be a functioning as part of the landscape.

Native plants are those that occur in a region where they have evolved specific physical and chemical characteristics to survive in a specific environment. These evolutionary traits are responses to the biotic environment such as disease, insects, inter- and intra-species interactions, and the abiotic environment such as soil type and the climatic patterns that surround them.

The use of native plants for ornamental landscaping has multiple benefits including preserving regional genetic diversity, using plants with natural resistance to local pests and diseases thus eliminating or decreasing the need to use harmful pesticides/fungicides, and providing natural plant habitat for wildlife. Native plants also require less overall maintenance due to their natural ability to survive in their environment.

Using native plants does not translate to taking plants growing in the wild. The best practice is to either propagate native plants from seeds collected in the wild or purchase nursery grown native plants. Native plants are abundantly available at local nurseries and often can be purchased at local botanical gardens. Although native plants are not essential for a green roof's success or environmental benefits, it is a viable and thoughtful alternative to typical green roof plant material.

October 2006
Living Roofs, Inc. is currently experimenting with pre-grown (quart size) native herbaceous plants for green roofs. The 20 species being tested are hardy, drought tolerant perennials indigenous to North Carolina. Some of the species are deciduous and die back during the winter, while others retain either an evergreen basal rosette such as Eastern horse-mint (Monarda punctata) and narrow-leaf silk grass (Pityopsis graminifolia var. latifolia), or are truly evergreen such as path rush (Juncus tenuis) or pink showy primrose (Oenothera berlandieri).

Many native species that live in xeric environments have evolved a tap root enabling them to reach moist soils further bellow the soil surface. Tap-rooted species such as big bluestem (Andropogon gerardii), false indigo (Baptisia australis), and rattlesnake master - yucca (Eryngium yuccafolium) are being tested in this experiment and it will be interesting to discover if tap-rooted plants can survive by sending their tap root laterally along the bottom of the green roof soil medium rather than vertically.

This experimental green roof is 4 feet x 8 feet and has a 6-inch growing medium depth simulating a semi-intensive green roof. This depth was chosen as it does not create as harsh of an environment as a thin 4-inch extensive green roof, thus increasing the native perennials chances of survival. The growing medium is a blend composed of 60% Permatill (coarse expanded slate), 30% sand, and 10% compost. The test site receives full sun to part sun.

The following native species are being tested (quart size):
Allium cernuum (wild nodding onion)
Andropogon gerardii (big bluestem)
Baptisia australis (false indigo)
Coreopsis palmate (stiff tickseed)
Echinacea purpurea 'Kim's knee high' (purple coneflower)
Echinacea purpurea 'Kim's mop head' (purple coneflower)
Eryngium yuccafolium (rattlesnake master - yucca)
Juncus tenius (path rush)
Liatris microcephala (dwarf gayfeather)
Monarda punctata (Eastern horse-mint)
Oenothera berlandieri 'Siskiyou' (pink showy primrose)
Oenothera fruticosa (sundrops primrose)
Panicum virgatum 'heavy metal' (switchgrass)
Penstemon smallii (Small's beard tongue)
Phlox nivalis (pineland phlox)
Phlox paniculata 'David' (white garden phlox)
Pityopsis graminifolia var. latifolia (narrow-leaf silk grass)
Rudbeckia fulgida var. sullivanti 'Goldturm' (black-eyed Susan)
Salvia azurea (azure sage)
Schizachyrium scoparium (little bluestem)
Symphyotrichum grandiflorum (large flower aster)

Niche Gardens, Chapel Hill, NC, and the North Carolina Botanical Garden, Chapel Hill, NC proudly provided the plants for this experiment.

Evergreen Native Species
It is important to test evergreen species as they provide greenery during the winter months. Because there are few native evergreen herbaceous species that live in xeric environments, it may be necessary to combine them with non-native evergreen species to achieve a regular vegetative cover.

Experiment Construction
Ninety percent of the lumber used to build the experimental green roof is reclaimed. Using reclaimed wood extends the life of the lumber, rather than ending up in a landfill. The reclaimed wood was purchased at the Habitat for Humanity Reuse Center in Raleigh, NC.

Collaborative Trials:

February 2007
Living Roofs, Inc. and affiliates of the North Carolina Botanical Gardens (Chapel Hill) are performing trials to determine the success of seed germination and establishment of select species on green roofs. Particularly, the trial was established to test the success rate of seed germination and establishment in both lightweight green roof growing medium and common potting soil. The green roof growing medium blend is composed of 60% Permatill (coarse expanded slate), 30% sand, and 10% compost.



The following species are being tested from seed:
Achillea filipendulina (Gold Yarrow)
Achillea millefolium (Yarrow)
Asclepias tuberosa (Butterfly Weed)
Aster novae-angliae (New England Aster)
Buchloe dactyloides (Buffalo Grass)
Callirhoe involucrata (Wine Cup)
Chrysanthemum leucanthemum (Ox-eyed Daisy)
Chrysanthemum maximum (Shasta Daisy)
Cichorium intybus (Chicory)
Coreopsis lanceolata (Tickseed)
Echinacea purpurea (Purple Coneflower)
Gaillardia aristata (Blanketflower)
Helianthus maximiliani (Maximilian Sunflower)
Hesperis matronalis (Dame's Rocket)
Ipomopsis rubra (Standing Cypress)
Liatris pycnostachya (Gay Feather)
Liatris spicata (Dense Blazing Star)
Linum lewisii (Blue Flax)
Lupinus perennis (Perennial Lupine)
Oenothera missouriensis (Missouri Primrose)
Oenothera speciosa (Showy Primrose)
Papavaer nudicaule (Iceland Poppy)
Penstemon strictus (Rocky Mt. Penstemon)
Salvia coccinea (Scarlet Sage)
Salvia farinacea (Mealy Blue Sage)
Tetalostemum purpureum (Purple Prairie Clover)
Trifolium repens (White Dutch Clover)
Verbena rigida (Tuber Vervain)
Verbena tenuisecta (Moss Verbena)


Copyright 2006, Living Roofs, Inc. All rights reserved.