Downtown Storm-water Management

The first step was to remove and dispose of the existing aggregate. One-quarter-inch-per-foot tapered polyisocyanurate was then installed over the existing roof system. Baker Roofing put 1/2-inch coverboard over the new tapered ISO. A new adhered 0.080 white TPO membrane system with heat-welded seams was installed.

In addition, Baker Roofing removed the existing terra-cotta coping cap and custom fabricated and installed new 24-gauge coping for the perimeter. The crew installed new retrofit drain assemblies at existing drain locations and added two new overflow drainage scuppers. It was also necessary to replace the counterflashing and membrane flashing.

With the reroofing complete, the green roof could be installed over the entire rooftop. The Xero Flor Green Roof System is an extensive system (see “Green Roofs Defined and Explained”, page 4) that utilizes prevegetated mat technology engineered in Germany and refined during 40 years of continued research and development. The mats are rolled out like sod on rooftops. They are installed atop three system components—a retention fleece, drain mat and root barrier—which are
also delivered in rolls for ease of installation.

Xero Flor green roof mats are rolled out like sod on rooftops. They are installed atop three system components, which are also delivered in rolls for ease of installation.

The retention fleece is a layer of non-woven fabric directly under the pre-vegetated mats themselves. It facilitates the distribution and temporary storage of rainwater. The drain mat, a geotextile fabric under the retention fleece, ensures excess water flows to roof drains and does not stay on the roof. Placed right over a roof’s waterproof membrane, the root barrier is a
durable plastic layer that prevents root encroachment and protects the membrane. Because of the geotextile that is the basis of the mats in the Xero Flor system, sections of the green roof can be rolled up and then rolled back into place if necessary to access the underlying roof for inspection or repairs.

Xero Flor systems weigh 8 to 10 pounds per square foot with options up to 25 pounds per square foot. These green roof assemblies work on basic flat roofs, roofs with dynamic shapes and even on slopes up to 45 degrees.

“While Xero Flor technology has European roots, all our system components for projects in the U.S. are 100 percent American-made,” notes Clayton Rugh, Ph.D., general manager and technical director, XFA. “In addition, we grow our green roof mats at independent, locally owned farms across the country. Using local horticultural suppliers supports more sustainable agriculture and gives a boost to local economies, too.”

On the roof atop its headquarters, XFA showcases three different plant palettes: the Appalachian Plant Mix, Southern Plant Mix and Mid-Atlantic Plant Mix. Each features 12 to 15 varieties of plants, primarily different types of sedums, which are known for their hardiness. Xero Flor pre-vegetated mats for the entire Southeast U.S. region are grown in northeast Durham County.