With Tremco’s Help, the William J. Clinton Presidential Library Makes History as the Only Library of Its Kind With a Sustainable Vegetated Roof System

Oct. 10, 2008


Having been built three years before, in 2007 the William J. Clinton Presidential Library was ready for its finishing touch—a state-of-the-art, eco-friendly vegetated roof.

Tremco Roofing and Building Maintenance and its general contracting subsidiary, Weatherproofing Technologies Inc (WTI), were awarded the vegetated roof project with a creative, practical and environmentally conscious roof design.  Tremco and WTI presented a comprehensive roofing system plan that encompassed essential waterproofing techniques, usability and beauty through high-end landscaping, assumption of all roof liability and budget compatibility.

Furthermore, Tremco met the National Archives and Records Administration's (NARA) water, fire and pest-proofing requirements. The NARA is responsible for protecting documents and materials that are created in the course of business conducted by the United States federal government, many of which are stored in presidential libraries.  

Delivering a precedent-setting project on a tight time frame
With installation originally targeted for a narrow eight weeks, the time frame was reduced to just five weeks after work had already begun. This was in order to take advantage of a rooftop news opportunity in which C-SPAN interviewed President Bill Clinton. To accommodate the crunched timeline, Tremco and its crew overlapped steps and worked late nights.

"It was a pleasure to work with some very creative minds on this project," said Mark Anderson, Tremco's sustainable design architect and project manager. "With the timeline compressed by 40 percent, all subcontractors needed to orchestrate their trade with precision. Many things were assembled off-site, so the actual installation time was reduced. Even the serpentine boardwalk was designed on AutoCAD and built in pieces off-site so it could be assembled like a quick jigsaw puzzle," he explained.

As the general contractor, WTI provided daily on-site project management and was responsible for completing the vegetated roof project within specifications, on time and on budget. In addition, Tremco guarantees the quality of its work and products with a 20-year warranty, as well as a three-year warranty for vegetation establishment.

Arkansas-friendly plants are stored prior to planting on the vegetated roof on the William J. Clinton Presidential Library.

Increasing building and roof durability while offering unique energy- and cost-savings benefits
Unlike a traditional roof, a vegetated roof system insulates the building and extends the life of the roof with significantly more eco-friendly results. Storm water is filtered and, as it runs through the roof garden, its flow is slowed. The roof can also retain storm water and release it slowly. A slow, consistent flow of water, rather than the fast, varied amount present during a storm, also benefits sewer systems.

HVAC systems benefit, too. Because a vegetated roof offers some thermal insulation and evapotranspiration cooling, HVAC systems can operate at increased efficiency, which can lead to reduced heating and cooling costs.

"This project was designed to be a very lush, long-lasting, high-performance environmental statement," Anderson said. "There are very few vegetated roofs with this level of complexity, beauty and usability."

Creating an eco-friendly roof in line with the Clinton Climate Initiative
Compared to traditional roofing systems that can contribute to an urban heat island effect, vegetated roofing systems reduce greenhouse gas through plant CO2 absorption and by reducing fossil fuel energy usage.

"[This roof] has two environmental purposes," said President Clinton in a C-Span interview that was cablecast November 26, 2007. "One is, it will absorb carbon dioxide and cool the building. That is, when you have a green roof like this, the greenery will absorb carbon dioxide, and it will keep heat out of the building so it will lower the air conditioning demands of the building. Or, in the wintertime, it will lower the heating demands of the building. And, therefore, our energy bill will go down.

"The second thing this does," Clinton continued, "is to efficiently use and capture the rain water so it's not just run-off; it's not just wasted. And we don't have to spend energy and water coming up here and watering the plants as much. The more you can absorb and recycle rainwater, the less regular water you have to use; the less energy you use."

Just before winter, turf was meticulously installed on the vegetated roof on the William J. Clinton Presidential Library.

Constructing a vegetated roof
Throughout construction, Tremco was on-site every hour to manage the complete process.  First, the existing ballast and insulation were temporarily removed to upgrade the existing waterproofing to a very long-life roof system.  After thorough leak testing, the insulation was reinstalled along with all protection and drainage components.  The architectural hardscaping elements, growing media and plantings provide a spectacular living roof space to an area that was previously unused. 

Growing green above ground
Planting maintainable green life over concrete several stories above the ground is a challenging task. Directed by Tremco and its contracted experts, subcontractors spread and molded 135 cubic yards of unique growing medium over the library's concrete roof. The medium features separate layers of Arkalite, Stalite and sand. Arkalite starts out as local east Arkansas clay. It is then super-heated to produce a man-made version of lightweight volcanic rock. It serves as the bottom stratum in the soil design to increase depth and assist with irrigation and drainage. The primary lightweight growing medium was a special blend of Stalite (expanded slate), compost, worm castings and more designed to help the landscape keep its form and provide nutrition to the plants.

Tremco also employed a sub-surface KISSS irrigation system—one that combines a capillary mat with a slow-drip process that keeps the growing medium properly irrigated at all times, even during dry weather.  This design uses 80 percent less water than an overhead system.  Tremco's on-staff environmental horticulturist approved 80 different species from which 9,280 plantings were made. 

"When it grows out, this will look like a lush carpet," remarked Clinton in the C-Span interview.

On traditional roofs, retaining storm water to keep a moist roof and clear sewers and to manage water runoff would be ill-advised for fear of leakage.  With Tremco vegetated roofs, however, comprehensive leak test systems are installed.  Using the most current electronic vector mapping available, a conductor wire is placed around the perimeter of the roof.  This creates a low-voltage charged plane both above and below the waterproofing membrane.  The vector mapping system can detect leaks within one square inch of a potential leak entry area.

Providing functionality
The only vegetated roof system on a presidential library in the United States, Tremco's history-making roof adds beauty and usability to both a distinguished venue and unique geographical site.  This natural, living roof replaces the green space that was displaced during the construction of the building.  Strategically placed over the entire surface of the roof are plants native to the environment, vine-covered trellises, musical wind chimes made of organ pipes, benches and elaborate decking.  On the naturally windy roof, the chimes allow for musical medleys, while the trellises act as wind buffers for visitors' comfort.  

The boardwalk, created so precisely that 743 individually numbered pieces of wood were used, was designed to simulate the flow of the Arkansas River complete with an oxbow.  For extended beauty and durability, 380 linear feet of glass panels set in a framework that reused the original railing defines the perimeter of the roof. 

Trellis structures and seating areas on the roof were made of recycled steel.  So that construction materials were not disposed of in landfills, existing roof materials were reused when possible.  The library is an outstanding example of energy and environmental design, elevating its status from LEED-NC Silver to the prestigious LEED-EB Platinum certification.  The highest certification a building can receive, this rating is awarded to organizations with green buildings that strive to make them greener. 

A view of the south vegetated roof on the William J. Clinton Presidential Library.

Long-term advantages
Tremco not only provides clients like The Clinton Foundation and the William J. Clinton Presidential Library with immediate solutions and total project management but also provides sustainable material and technical solutions, turnkey project management, and long-term roof maintenance.

The library roof provides distinct advantages to the library and the environment.  It assures the detection of potential future leaks, the spreading of sedum plants (and, within three years, providing 85 percent green coverage), a three-year establishment warranty on all plants, plus a 20-year warranty, including periodic inspections, on the complete roof system.  Capturing usable water, insulating the building, reducing greenhouse gas emissions and providing a natural, living biosphere are just a few of the benefits this roof will continue to give to the library and the environment.

To learn more about how an on-time, sustainable and beautiful roofing solution can benefit both your organization and the environment—as well as help you trim long-term costs—visit the Tremco Web site at www.tremcoroofing.com or call 800-892-1872.

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