Using Engineered Geofoam for Garden Roofs

For most of the past century, the rooftops of commercial and institutional buildings have largely been places to locate unsightly mechanical systems. Architectural treatments, such as parapets and screens, provide visual relief from such equipment. Now, roofing professionals and building owners increasingly look at the roof as “found space”—a place to be planted and used, instead of hidden.

Facebook’s Frank Gehry-designed MPK 20 building sports a 9-acre green roof using EPS geofoam from Insulfoam.

Facebook’s Frank Gehry-designed MPK 20 building sports a 9-acre green roof using EPS geofoam from Insulfoam.

Throughout the U.S., garden roofs (or living roofs) are growing in popularity with more than 5.5 million square feet installed in 2014, according to Green Roofs for Healthy Cities. Most of that total was for private rather than public projects, indicating this is not just a government trend. In addition to providing attractive and usable open space, garden roofs offer environmental benefits, such as helping to slow and filter urban run-off.

Some of America’s largest companies have installed green roofs. Ford’s Dearborn, Mich., truck plant final assembly building sports one of the world’s largest living roofs at 454,000 square feet. In 2015, Facebook opened its MPK 20 office building in Menlo Park, Calif., with a 9-acre living roof featuring a 1/2-mile walking trail and more than 400 trees.

If you haven’t worked on a garden roof yet, it is likely only a matter of time until you do.

Addressing the Challenges of Garden Roofs

Weighing a fraction of soil, EPS geofoam fill creates ultra-lightweight landscaped features on Facebook’s garden roof.

Weighing a fraction of soil, EPS geofoam fill creates ultra-lightweight landscaped features on Facebook’s garden roof.


Adding plants and park-like amenities to a roof increases the complexity of the roofing assembly. Garden roofs present two primary challenges for roofing professionals to solve: minimizing the dead load and preventing moisture intrusion.

The project team for the Facebook MPK 20 building’s green roof met this two-fold need—and more—with expanded polystyrene (EPS) geofoam.

Weighing considerably less than soil, EPS geofoam is an ultra-lightweight engineered fill that can be used to create contoured landscape features, such as hills and valleys. The material weighs from 0.7 to 2.85 pounds per cubic foot, depending on the product type specified, compared to 110 to 120 pounds per cubic foot for soil.

Despite its low weight, EPS geofoam is designed for strength and has better load bearing capacity than most foundation soils. Geofoam’s compressive resistance ranges from approximately 2.2 psi to 18.6 psi (317 to 2,678 pounds per square foot) at a 1 percent deformation, depending on the product.

The garden roof on Facebook’s MPK 20 building provides ample open space and a half-mile walking trail for employees.

The garden roof on Facebook’s MPK 20 building provides ample open space and a 1/2-mile walking trail for employees.

EPS geofoam is also effective at addressing the second challenge of garden roofs: managing moisture absorption. The moisture performance of the various components in a green roof assembly is critical; retained water imposes additional loads on the roof and increases the risk of water damage to the roof assembly. EPS geofoam meeting ASTM D6817 standards works well here as it only absorbs 2 to 4 percent moisture by volume, even over long-term exposure, and it dries quickly. The moisture performance of EPS has been demonstrated in extensive in-situ applications and real-world testing, including research conducted by the U.S. Army Corps of Engineers’ Cold Regions Research and Engineering Laboratory. After burying EPS in wetted soil for nearly three years, the lab found that the material absorbed only 1.7 percent moisture by volume.

In addition to enabling lightweight, durable landscape features and helping to defend against water, EPS geofoam provides thermal insulation in garden roofs. Roofing professionals have used EPS insulation in roof assemblies for decades because it offers the highest R-value per dollar among rigid foam insulations.

Expect More Demand

Although green roofs currently account for a small portion of the billions of square feet of roofs in the U.S., expect to see more demand for them given their aesthetic and environmental benefits. High-performance materials, like EPS geofoam, can help provide a long-lasting, durable green roof assembly.

PHOTOS: Insulfoam

NRDC and EDC Sue EPA Over Stormwater Standards

The Natural Resources Defense Council (NRDC) and the Environmental Defense Center (EDC) have sued the Environmental Protection Agency (EPA) to strengthen standards to prevent pollution from stormwater, one of the nation’s most widespread forms of water pollution. More than a decade ago a federal appeals court ordered EPA to strengthen those protections, but the agency has failed to take action.

The dirty water that runs off roads, parking lots and other hard surfaces in cities and suburbs when it rains is the prime cause of beach closings around the country, and is responsible for fouling tens of thousands of miles of streams and hundreds of thousands of acres of lakes, ponds, and reservoirs. In addition, sediment-laden runoff from forest roads threatens drinking water supplies and kills fish and other aquatic life.

“This inexcusable delay in obeying a clear court order is, unfortunately, all too typical of EPA foot-dragging on the crucial stormwater pollution problem. The agency has repeatedly promised a much-needed update of all its stormwater protections, and repeatedly failed to come through,” said NRDC senior attorney Larry Levine.

The suit, filed late Thursday with the U.S. Court of Appeals for the Ninth Circuit in San Francisco, charges EPA has failed to implement that court’s 2003 ruling ordering the agency to correct and strengthen rules for urban runoff that flows through municipal sewer systems. EPA also ignored the same court’s order to decide whether it has an obligation under the Clean Water Act to regulate runoff from forest roads that wash damaging sediment into water bodies. The ruling in EDC v. EPA resulted from a successful challenge brought by EDC and NRDC against EPA’s 1999 stormwater regulations.

“EPA’s failure to act deprives the public—and the environment—of the important clean water victory that EDC and NRDC achieved over ten years ago. Our waterways continue to remain at risk from stormwater pollution, which threatens public health, wildlife, and recreation. ” said Maggie Hall, Staff Attorney at EDC.

In urbanized areas, according to the suit, stormwater “picks up contaminants, including suspended metals, algae-promoting nutrients, used motor oil, raw sewage, pesticides, and trash,” that flows untreated through municipal sewer pipes directly into streams, lakes and the ocean. It is, the suit says, “one of the most significant sources of water pollution in the nation, at times comparable to, if not greater than, contamination from industrial and sewage sources.”

The appeals court found that EPA’s urban runoff rules for communities with populations under 100,000 don’t comply with the Clean Water Act because they rely on self-regulation by local municipalities and don’t allow for public participation when local pollution controls are being set.

Unpaved forest roads throughout the West are a major threat to water quality, undermining the billions of dollars that is spent on the recovery of native runs of salmon and steelhead, and harming other valuable fisheries and drinking water supplies.

In 2003 the court said the agency had given no justification for its failure to regulate runoff from forest roads and ordered the agency to address this issue.

In 2009, EPA announced it would undertake a major overhaul and upgrading of its urban stormwater rules, which NRDC and EDC welcomed as an opportunity for the agency to obey the court order on urban runoff. NRDC also encouraged the agency to promote green infrastructure—roof gardens, permeable pavements and the like—that would allow more rainfall to soak directly into the ground, and sharply limit runoff volume.

However, EPA never completed the new rules and recently disclosed it was abandoning the effort. EPA had been under heavy pressure from developers not to act.

EPA announced in 2012 that it was considering options for regulating forest road runoff, and that regulation may be appropriate. However, the agency has offered no timeline for a decision.

In the lawsuit, EDC and NRDC seek a court order imposing clear deadlines for EPA to act. “We hope this suit spurs EPA to get back into the business of modernizing its whole stormwater program, which badly needs updating and could greatly benefit from new green technologies,” NRDC’s Levine said.

Read more about this issue and the lawsuit, and find the pdf of the lawsuit at Larry Levine’s blog.