A green roof is a vegetated layer installed over a waterproofing system on top of a flat or slightly sloped roof surface. At our demonstration site, a tabletop-scale model illustrates the layered construction and plant performance of an extensive green roof system using hardy sedum, yarrow, hyssop, euphorbia, and gaillardia species.

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The Problem:
Conventional rooftops are impervious surfaces that shed virtually all rainfall as runoff. In residential and commercial settings, roof area often represents the single largest contributor to stormwater volume on a property. That runoff carries pollutants, causes erosion, and contributes to downstream flooding.
The Solution:
Green roofs intercept rainfall at its source. The growing media absorbs water, plants take it up through their roots and release it back to the atmosphere through evapotranspiration, and the drainage layers slow any excess before it leaves the system. Even a shallow extensive green roof system can dramatically reduce the volume and velocity of stormwater leaving a building.
Costs
Green roof installation costs vary widely depending on scale, structural requirements, and plant selection. For extensive systems, typical costs range from $15 to $30 or more per square foot including all materials and labor. Smaller residential or demonstration-scale installations may have higher per-square-foot costs due to fixed mobilization expenses.
Design Considerations
Key engineering considerations include structural load capacity, waterproofing integrity, drainage design, wind uplift resistance, and plant selection appropriate to the local climate. In Georgia, heat tolerance and drought resistance are essential plant selection criteria. Green roofs may be installed on rooftops with slopes of up to 25%, but are not generally recommended for use on rooftops with slopes greater than 10%.

See the in Action

The demonstration display uses a table-mounted model that shows both a conventional shingled roof surface and a green roof surface side by side. Rain simulator sprayers deliver water to both surfaces, allowing visitors to observe the difference in runoff behavior in real time.

Practice Type: Rainfall interception and evapotranspiration

Scale: Tabletop display (3.5 ft. x 8.0 ft.)

Key Plants: Sedum species (drought-tolerant succulents)

Best For: Rooftops, covered structures, educational displays

Runoff Reduction: Green roofs can retain 60% of rainfall on the roof surface

Maintenance

Task
Frequency
Details

Inspect plants

Monthly during growing season

Check for dead or sparse areas; replant as needed with same Sedum species

Weed removal

As needed

Remove any volunteer plants that could displace Sedum or compromise root barrier

Irrigation check

Monthly

Verify moisture sensor function and spray head coverage

Drainage inspection

Twice yearly (spring and fall)

Ensure drip edge and gutters are clear of debris; check for ponding

Membrane check

Annually

Inspect waterproofing where accessible for cracks, tears, or lifting