Duke University Hospital has earned an award for environmental stewardship and design excellence for its 2007 heliport roof replacement project. The Washington, D.C.-based Center for Environmental Innovation in Roofing presented the award in February during the 2009 International Roofing Expo. The Duke project reused nearly 90% of existing construction materials and diverted 718 tons of solid waste from the landfill. High-value roofing insulation was salvaged, recertified, and now installed in four other buildings on campus, including a new vegetated green roof over the hospital’s main entrance. The Center’s Executive Director, Craig Silvertooth, explains that the Duke Hospital roof project perfectly illustrates the intent of the Center’s 2009 Excellence in Design awards program.

The one sustainability strategy that set the Duke project apart from the others was the adaptive reuse of the roofing material. “That was very attractive to them. They were impressed by the salvage value we had on the project,” says Tim Pennigar, construction project manager at Duke Health System. “The Carver Hawkeye Arena at the University of Iowa was runner-up, and it also had a lot of material reuse. Anticipating the second generation of a roofing system has become an important marker of good, sustainable roofing design.”

The main factor that led to the reuse of the heliport roof lies in the former roof’s assembly. The roof was built as an inverted roof membrane assembly, also known as IRMA or more recently as “protected membrane roofing”, which protects the membrane from destructive sunlight, environment, and physical abuse. Flipping the conventional roofing approach in which the membrane lies on top of the assembly, the protected membrane roofing approach places it on the bottom of the assembly where it’s either protected by a layer of insulation, such as extruded polystyrene, ballast, or pavers.

Pennigar, who has been at Duke for 23 years handling roofing construction, says he has seen a lot of otherwise useful materials thrown in the landfill. He blames both a lack of sustainability knowledge within the culture and a lack of forward-thinking design. “Either no one knew what to do with [the material]—which is quite often the case—or it wasn’t really thoughtfully designed and the way it’s assembled you can’t break it down into its individual parts without destroying it.

“So this [roof] was our first chance to test what we had been doing. We knew this was a better way of doing things. And this was an opportunity to demonstrate it. There is some real bottom-line benefit to this; it can actually produce money.”

The building had a single layer of roofing membrane that was fully adhered to the concrete back, so instead of tearing all of it off, Duke left it in place after obtaining some code variance to do so. “I have to be careful suggesting that people can keep covering over roofs, roof after roof after roof. In this situation we had no problem leaving that membrane in place, patching it up, and using it as a temporary roof during construction. Doing a roofing tear-off creates some serious exposure for your building, particularly in a healthcare environment, so we really loved the idea of being able to leave that in place and keep the building fairly dry while we did the rest of the project.”

Pennigar and his team removed the extruded polystyrene (XPS) insulation, wrapped it up, craned it to the ground, and stockpiled it at a farm property that Duke owns. The Dow Chemical Company was the original provider of the XPS, which is a closed-cell insulation. The company sampled the insulation and found it had 94% of its original R-value after 20-plus years on the roof, Pennigar says. “It was still performing great, and they recertified it as if it was brand new.”

An old, decomposing filter fabric that that was between the ballast and the insulation was the only material from the existing assembly that went into the landfill. The team removed the existing stone ballast with an industrial vacuum truck and reused it in road stabilization projects.

The reclaimed XPS was used on four other facilities, including the Durham Regional Hospital and a green roofing project. “The laundry facility’s roof system allowed us to leave it in place and go over it with a new system,” Pennigar says. “In all the projects we did, we were lucky enough that they were the kind of construction that will allow us to reuse in place. So we basically put a new membrane over this existing [system] and added the additional insulation that gave it some additional thermal value to get it up to correct codes. And then we ballasted it.”

The green roofing project on Duke Hospital’s main entry also used the reclaimed insulation. Duke is using this roof section, covered with sedum, as a green test site. “That first project, the heliport project, really kind of jazzed us up here, to be honest with you,” says Pennigar. “It was great to show that this [sustainability] really works, it’s not just feel-good stuff. We can actually save money, do right by the environment, and lead by example here. So little by little, we kind of came full circle: The insulation we took off the building went and reroofed other buildings, and eventually, a good portion of it came back to complete a vegetated roofing project on the hospital.”

Pennigar says this doesn’t just highlight the value of protected membrane roofing design, “it really suggests that any roofing assembly can be made to be very durable, high-performing, and reusable if we stop and really think forward a little bit.”

2007 Duke Heliport project by the Numbers:

  • 718 tons, or approximately 3,184 cubic yards, of solid construction waste diverted from the landfill
  • 2,120 miles of dump truck/landfill travel avoided per Waste Industries, Inc., calculations
  • $29,797 in landfill dumping fees avoided by Duke University Hospital
  • 90,000 square feet of existing membrane recycled in-place as temporary roofing to keep building dry during installation of a new fully adhered 45-millimeter thermoplastic membrane with protected membrane roof covering of 3" XPS panels
  • 289,000 board feet of XPS insulation salvaged and preserved for future reuse (Certified at 94% of its original R-Value)
  • $133,600 approximated retail value of salvaged XPS roofing insulation
  • Number of subsequent Duke buildings to date that have been reroofed with the XPS insulation salvaged from the 2007 Heliport project: 4 (Duke Civitan Building, Durham Regional Hospital laundry facility, Duke Hospital main entry [vegetated roof], Duke Hospital courtyard plaza roof)
  • Anticipated service life for new roofing assembly: 30+ years (Number of leaks reported to date: 0)
  • Number of needless roof penetrations avoided by use of portable equipment supports: 134