by ArchitectureWeek

The 1925 art deco-style Montgomery Ward Catalog Building in Baltimore, Maryland has just undergone a rehabilitation. The adaptive reuse project by DMJMH+N, an architecture/ engineering firm in Washington D.C., restored the facade of the landmark building and installed a 30,000-square foot (2800-square-meter) "green" roof.

Now home to the State of Maryland's Department of the Environment, the renamed "Montgomery Park Business Center" had been an abandoned brownfield site for 15 years. The urban revitalization project preserves some of Maryland's valuable open land by providing new office space without causing further sprawl. And the 1.3 million-square-foot (120,000-square meter) warehouse conversion both preserves historic integrity and fulfills the high-technology needs of modern business tenants.

With only small adjustments to the already sturdy structural system, the one-story roof over a former train shed was covered with an extensive green roof.

In this context, "extensive" refers to a low-maintenance groundcover in shallow soil, which collectively weighs little more than a conventional roofing system. (This contrasts with "intensive" roofs with deeper soil and diverse plantings, which require higher maintenance and more substantial structural support.)

A waterproofing, root-resistant, single-ply roofing system was applied, then covered with 4-inches (10-centimeters) of soil. This soil is 75 percent inert — mixed with expanded slate — to keep the depth of the soil from decreasing over time.

Plants selected for the roof are indigenous to alpine environments. Even though the building is near sea level, these plants were chosen because they are hardy even under extremes of temperature, wind, and drought. They grow rapidly to form a dense vegetation mat with shallow roots, thriving even in harsh soil conditions.

The low-lying plants for the Montgomery Park green roof were supplied by Green Roof Plants. According to president Ed Snodgrass, these plants provide maximum groundcover, water retention, erosion resistance, and respirative transpiration of moisture.

The alpine plants also have fibrous roots to protect roofing membranes, and they impose no special irrigation or nutritional requirements. Snodgrass notes the importance of architects collaborating with local horticulturists to determine an optimal plant list for each project.

Green roofs can reduce the surface temperature of a roofing membrane
significantly — by up to 40 degrees Fahrenheit (22 degrees Centigrade) on hot sunny days. This buffering can double the life expectancy of the membrane, while reducing the "urban heat island" effect. The green roof at Montgomery Park is expected to reduce runoff by about 76 percent.

Furthermore, green roofs cool the surrounding air significantly by respirating the retained water. They can absorb airborne toxins and return oxygen to the air. And they can provide substantial noise insulation below and support biological habitat above.

The DMJMH+N design team was led by Werner Mueller, AIA. Montgomery Park owner/developer is Samuel Himmelrich.

Alpine plants on an expanse of roof will soon grow to complete "ground" cover. Photo: Emory Knoll Farms Typical layers in a green roof system, from bottom up: roof structure, waterproof roofing membrane, root barrier, drainage and water retention material, soil, and vegetation. Image: American Hydrotech, Inc. A 1925 Montgomery Ward Catalog Building in Baltimore, Maryland transformed by DMJMH+N into the Montgomery Park Business Center. Photo: Dan Cunningham A 1925 Montgomery Ward Catalog Building in Baltimore, Maryland transformed by DMJMH+N into the Montgomery Park Business Center. Photo: Dan Cunningham The staging area for plants awaiting "installation" on the building's "green" roof. Photo: Emory Knoll Farms Workers planting the specially prepared roof. Photo: Emory Knoll Farms A typical extensive green roof. (Not the details used in the Montgomery Park project.) Image: American Hydrotech, Inc. Typical drain in an extensive (top) and intensive (bottom) green roof. (Not the details used in the Montgomery Park project.) Image: American Hydrotech, Inc. Interior of the former Montgomery Ward train shed; the skylight peaks through the surrounding green roof. Photo: Dan Cunningham   Click on thumbnail images to view full-size pictures.