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Chadwick Arboretum & Learning Gardens

College of Food, Agricultural, and Environmental Sciences


Green Roof on Howlett Hall

In August 2013, the Green Roof on Howlett Hall was installed in the Chadwick Arboretum & Learning Gardens – the first retrofit green roof at The Ohio State University. This 12,000 square foot green roof is located on Howlett Hall, home to the OSU Department of Horticulture & Crop Science, Department of Food Science and Technology, and the Chadwick Arboretum & Learning Gardens Headquarters. This site is an ideal location with high visibility, handicap access, and easy walk-out access from the main entrance of the building, allowing it to be a demonstration for future green roofs not only in Columbus, Ohio but in the world. Stop by and enjoy a beautiful garden where an industrial, barren, asphalt roof once stood.


Click on the image below to see our Green Roof installation as a time-lapse video. After years of planning, design, and fund raising the actual installation – from the water proof membrane to beautiful plants – was completed in 14 days.

Read more about green roofs in general and specifically about the Chadwick Arboretum & Learning Gardens Green Roof on Howlett Hall below:

What is a Green Roof?

Simply put, a green roof is a living, breathing vegetated cover over a built structure. There are two main classifications when discussing green roofs: extensive and intensive. The differentiation is primarily in the depth of the growing media. Extensive green roofs are lighter weight and typically less expensive, but have limitations in planting design. Intensive green roofs are heavier and therefore suitable for structures with a strong load bearing capacity. The depth of growing media on an intensive green roof ranges from 6–18 inches and therefore offers a broader palette for design and plant selection, but it costs more than an extensive roof.

Extensive vs Intensive Green Roofs
Extensive Roof Intensive Roof
3"–6" growing media depth 6"–18" growing media depth
Sedums Plant design options
Weighs: 15–35psf Weighs: 35–30psf
Cost: $13–$25 psf Costs: $25–$50 psf
Why Green Roofs?

Based on normal annual rainfall, the Green Roof at Howlett Hall will prevent over 200,000 gallons of polluted water from entering the Olentangy River each year and provide a projected annual savings of $10,374 in energy costs and roof maintenance. Green roofs offer the most benefit when implemented in mass, but even one green roof provides the following environmental and economic benefits: 

  • reduces, delays, and filters storm water runoff
  • adds insulation and energy efficiency, reducing summer air conditioning costs
  • increases green space and biodiversity
  • lessens the “Urban Heat Island” effect by cleaning and cooling the ambient air to improve air quality
  • increases urban food production and food security
  • sequesters or stores carbon dioxide from the atmosphere
  • lengthens roof lifespan, diverting waste from the landfill
  • adds property value for healthier and more prosperous communities


The OSU Green Roof on Howlett Hall

In urban developments like The Ohio State University campus, sewage flows naturally to publicly owned treatment works (POTW) during dry weather, where harmful pollutants are removed before returning water to the environment. During wet weather, however, rainwater does not percolate back into the ground as it was intended to do. Instead, it falls on paved surfaces such as roads, parking lots, and buildings, collecting debris and pollutants on its way to the nearest sewer opening. At OSU, this polluted water combines underground with our wastewater system and, in the event of a heavy rain, overflows directly into our local Olentangy River through combined sewer outlets (CSOs).

With an average annual rainfall of 37 inches, the Green Roof on Howlett Hall would mitigate a minimum 22.8 inches (60% mitigation) compared to the surrounding parking lots. The green roof coverage of 12,000 square feet will reduce the impact to the Olentangy River by approximately 976,000 liters (approximately 250,000 gallons) of water each year.

Scarlet, Grey & Green and Our Mission

Green Roof DedicationTo support the momentum of the Ohio State sustainability efforts, the Chadwick Arboretum & Learning Gardens mission was to develop a prototype green roof that is visible and accessible to students, faculty, staff, and visitors. Although each green roof project is unique based on its exposure to climate elements (sun, wind, and rainfall), the purpose of this project was to document and streamline the best practices for green roof installation as a template to be used for future green roof installations campus-wide.

Further, as municipalities are required to comply with the Clean Waters Act, action must be taken to reduce the volume of contaminated water discharged into receiving waters. One approach is to integrate green infrastructure – such as a green roof – to mitigate storm water and slow its impact on the combined sewer outlets (CSOs).

History of Our Green Roof on Howlett Hall

The Green Roof on Howlett Hall project has been a long time dream. Since the early design stages of Howlett Hall prior to its construction in 1967, OSU had plans for a rooftop garden and therefore constructed the building to hold the additional load on the roof.  The major milestones, starting in 1967 when the building was built, are:

  • July 2014:  Open House with tours of our Green Roof
  • June 2014:  Ribbon cutting ceremony and reception for donors
  • September 2013:  Green Roof is complete and plants are established at their new site
  • Late Summer 2013:  Green Roof Installation began
  • 2011–2012:  Schematic and Development Phase; hired CTL Engineering and NBBJ architectural firms; fundraising continues with our second significant private donation of support received in the amount of $100,000
  • 2010:  Fundraising efforts begin in earnest with the receipt of our the first significant private donation of $100,000; roof replacement is approved; Green Roof
    Team hosts a statewide design charrette
    resulting in six basic design concepts
  • 2007–2008:  Research for a green roof at Howlett Hall is compiled. Green roof data is presented by student Megan (Ehrmin) Fleischer and Landscape Designer Professor Laura Burchfield at the Denman Undergraduate Research Forum.
  • 2004–2007:  Ohio Agriculture Research and Development Center (OARDC) sponsors green roof plot trials at Waterman Farm, but funding fails again (Dr. Martin Quigley and PhD Candidate Reid Coffman)
  • 1967–1969:  Howlett Hall is designed with a rooftop garden in mind, but funding is not allocated; Ken Reisch, Professor & Associate Dean of Horticulture at OSU and Dean Ramsey, Head of OSU Grounds & Facilities draw plans and schematics
The Green Roof Team

The Green Roof Team included the following professionals:

  • Mary Maloney, Director of Chadwick Arboretum & Learning Gardens
  • Megan Welsh-Meier, Program Coordinator, Certified Green Roof Professional, Higher Ground
  • Laura Burchfield, Horticulture and Landscape Design Professor
  • Rick VanDeusen and Glen Gerhart Sr. Project Manager, OSU Facilities, Operations,
    and Development (FOD)
  • John Woods & Ed Michelson, Landscape Architects, NBBJ
  • CTL Engineering
  • Roofmeadow
  • SMBH Structural Engineering
Frequently Asked Questions About Plants on the Green Roof
  • What is the best planting material for the Ohio Climate?
    Depending on the owner's main objectives, there are plants to choose for higher transpiration/air cooling rates, or there are specific plants to choose if color and aesthetics are the objective. Sedums, like stonecrop, are typically used because of their drought tolerance and transpiration rate.  Other local green roof sites are using herbs and native perennials like Tickseed, Dianthus, and Catmint.
  • What happens to the planting material in Ohio's cold months, and how does that effect the building's internal temperature?
    The plants go dormant in the winter, therefore the green roof goes dormant.  It still functions in terms of added insulation and roof membrane protection from harsh winter elements. However due to low transpiration rates in the winter, it is not as effective in terms of stormwater mitigation.
  • How many plants are on the roof garden?
    Chadwick Arboretum & Learning Gardens covered about half of the roof with a pre-grown sedum mat, with 11–14 varieties of sedum.  The other half was planted with 7225 perennial plants including sedum, Achillea (Yarrow), Rudbeckia (Black Eyed Susan), Festuca (Blue Fescue), Thyme, Lavender, Allium, Prairie Drop Seed, Geum and Sempervivum (Hens and Chicks)