Published on : March 01, 2011

Pros and Cons of Vegetated Roofing for Hospitals

Pros and Cons of Vegetated Roofing for Hospitals

Therapeutic gardens have been in use for thousands of years to help restore the health of those suffering from various ailments.  Yet, in modern hospitals these gardens have all but been replaced by sterile, built environments.

Today, healthcare facilities struggle with competitive pressures, a staggering expense of operations, and pressure to be more sustainable.  Many hospitals are turning to a more holistic approach of facility management to help alleviate economic and environmental pressures.  These new and retrofitted buildings are increasingly incorporating rooftop gardens into their facilities.

Benefits of a Rooftop Garden

Rooftop gardens, more commonly known as “green” or vegetated roofs, can provide compounding economic and environmental benefits to the buildings they adorn, and to the surrounding community.  As new green building trends emerge, the benefits of covering low-sloped roofs with vegetation are becoming widely known and practiced. 

Some of the benefits of vegetated roofing include:

  • Energy conservation
  • Storm water management
  • Extended life of the roof membrane
  • Mitigation of the Urban Heat Island effect
  • Much-needed habitat for native plants

Hospitals can reap even greater rewards with green roofs, through lowered stress levels of patients, visitors, and hospital staff that have visual access to vegetation. 

One of the most widely recognized benefits of adding a vegetated roof or wall is that it can significantly reduce the energy expenditure of the building.  One way they achieve this is by serving as added rooftop insulation, limiting the thermal transfer through the roof and keeping the indoor temperatures more stable. 

Roof membranes are hot.  When sunlight hits a roof, it turns from light energy into heat energy.  For example, on a 90 degree day a dark or gray roof membrane is generally between 160 – 180 degrees Fahrenheit.  Even white reflective membranes are still really hot – 108 – 121 on a 90 degree day.  The heat can soak down into the building from the roof and reflect inside through the windows.  Rooftop HVAC systems take in the air at those high temperatures and then have to cool it down to a comfortable level for the interior.

But when sunlight hits a plant, instead of turning to heat, it is converted into plant food – that’s what photosynthesis is all about.  Vegetation doesn’t get hot from sunlight the way that impermeable surfaces can.  On a vegetated roof, the temperatures are often lower than the ambient temperatures, reported at closer to 77 degrees on a 90 degree day.  That’s a significant reduction on the load for the rooftop HVAC system, which may then be downsized. 

Another cooling effect of vegetation is that after soaking up the water they drink, plants release it back into the air – a process called evapotranspiration.  This not only cools the building, but also helps to mitigate the Urban Heat Island effect of the surrounding community.  The Urban Heat Island effect is the reason why urban areas are much hotter than surrounding suburban and rural areas.  Impermeable dark surfaces, especially low-sloped roof membranes, are the major contributors to this effect.

Old Roof Maintenance and Removal

Roof maintenance and replacement is costly and time consuming for any building, but hospitals are especially affected.  Their re-roofing projects come with the economic burdens of not only the cost of the roof, but also the disruption to the facility’s operations.  Roofing is noisy, it’s smelly, and it often occurs in view of patient windows, creating privacy concerns.  Constantly patching a leaky roof brings added problems with water entry into the building – which can lead to mold, pests, air leakage, and a negative image of the hospital by patients and visitors who witness the leaks.

From an environmental standpoint, when the old roof membrane is removed, it is sent to a landfill where it is not likely to decompose for a long, long time.  After all, it is a waterproof membrane – and likely the size of the footprint of the building.  Then there are the environmental consequences of manufacturing and shipping the new roof membrane.  As much as the roofing industry is working on more environmentally friendly membranes, the options available right now for reliable waterproofing generally consist of asphalt, bitumen and PVC - not very friendly materials. 

The most economically – and environmentally – sustainable roofing practice of all is to keep the existing roof membrane protected, watertight, and on the roof for as long as possible.  Exposure to sunlight, weather, foot traffic, and the daily cycles of thermal expansion and contraction accelerate deterioration of roofing materials.  Plants, growth media, and all the layers of green roof components isolate the membrane and keep it preserved.  By protecting it from the elements, green roofs can extend the life of the roof membrane by double or more.  This isn’t a guess, it’s the industry standard.

When the roof does have to be replaced, the plants and growth media can either be reused or composted, and the other green roof components can be recycled. 

They aren’t Just Practical They are Pretty

But the greatest human aspect of green roofs is that they are beautiful!  They can be designed to look like a grassy groundcover, a flowering meadow, or a full service park with benches, sidewalks and trees. 

This is especially important for the many hospitals that are multi-level buildings, with inevitable window views of unsightly roofing membranes, mechanical equipment and parking lots.

Views of the built environment (human-made, rectilinear forms) are known to cause heightened stress, but views of nature have the opposite effect.  Looking at nature and greenery elicits relaxation, not just for patients, but also for visitors and hospital staff.  Studies show that patients with visual access to nature have lower blood pressure, fewer post-operative complications, and use fewer doses of strong narcotic pain drugs.  They receive more positive written comments from staff, and they have a greater overall satisfaction with the healthcare provider and quality of care, as compared to patients who can only see the built environment.  These studies imply that views of nature may enhance clinical outcomes and reduce hospital stays, thereby increasing economic benefits to the facility by reducing the cost of care.

With the high rates of turnover of hospital staff, a more beautiful, less stressful environment may help draw and retain employees and physicians.  It can also reduce stress levels for visitors, who might spread the word about their positive experience at the facility.  The layers of plants, growth media, and membrane protection can provide sound insulation to the building interior from helicopters, traffic, and construction noises, further reducing stress in patients and healthcare providers.

And there’s more!

Vegetated roofs provide countless benefits to the surrounding environment.  Plants improve air quality and sequester carbon dioxide.  They can reduce the water load for on-site and municipal storm water runoff systems by absorbing rain, and they improve the quality of rooftop runoff that does reach watersheds. 

They can provide a much-needed habitat for native plants and pollinators, all while reducing the overall cost of operating the facility and creating positive market identity.

In many municipalities, including New York City, Chicago and Los Angeles, rooftops are being used to grow vegetables and herbs – eliminating the fuel used for transport, extra packaging, and the use of chemical preservatives, because the food is harvested from overhead as needed.  It’s easier to monitor organic food production on-site rather than relying on costly organic certifications from far-away farmlands.  One municipal building in Portland, Oregon is using its rooftop garden to supplement over-extended food banks, contributing the veggie portion of hundreds of meals each season to local homeless shelters.

So what’s the downside?  What about the cost?  The extra weight?  Pollen? Maintenance?  And, the dreaded Leak…

Let’s start with leaks.  Every hospital Facility Manager’s nightmare is trying to chase down a leak.  It can be an endless process of flood testing, thermal scanning, patches and repairs, and ultimately leads to re-roofing.  But, there is a very cost-effective way to eliminate this whole process, through the use of electronic leak detection systems.  They are installed on bare roof membranes or underneath vegetated roof systems.  At any time during the lifecycle of the roof, if there is a leak or just a concern of a leak, the detection system can be used to locate even a pinhole break in the roof membrane, and show its location on the roof within a square foot.  The vegetated roof components can then be cut away just from that area, the repair made, and the components replaced.  There are several leak detection system options on the market which are very simple, inexpensive, long-lasting and highly effective.

And what about the cost - well, green roofs are expensive.  They are generally at least three times as costly to install as a traditional roof, and even more so if they are made accessible to visitors.  The costs can be offset or recovered over the lifecycle of the building through energy savings, extending life of the membrane, positive market identity and marketing, and through the benefits to patients and staff who view them on health care facilities.  However, while the life cycle cost savings may pencil out, some facilities just don’t have the capital for the upfront costs adding a green roof.

Green roofs are heavy.  Even the lightest green roofs generally weigh much more than traditional membranes.  Many facilities already have the structural weight capacity built in, but a structural engineer report is the first step in determining the viability of a green roof on an existing facility.  If the structure cannot support the weight, it is usually not cost-effective to build in extra structural support.  These buildings may not be good candidates for green roofs.

As far as pollen and other allergens, green roof plant selections should be species that do not create an abundance of pollen.  Any pollen aggravation is much more likely to come from the surrounding areas than from vegetated roof plants, if system is designed accordingly.

Green roofs do require maintenance.  It can be as infrequent as twice-annually for established low-profile systems, and more regularly for those that resemble park-like settings.  Each roof is different, and the designer or manufacturer should provide an operations and maintenance plan to the facility.  There are landscape services, experienced with rooftop garden maintenance, which can be utilized if the facility prefers not to maintain their green roof themselves.

The most important concept to consider when looking at vegetated roofing options is that each building, and in fact each roof section, may call for different green roof configurations.  There is no one-size-fits-all solution, and most industry professionals will emphasize the importance of using a green roof specialist to help identify the unique conditions of each roof section and assist in the coordination of appropriate plants, soils, components and maintenance. 

Every building has a roof; the vast majority of which are empty, hot and wasted real estate, contributing to the energy spend in the building, to the Urban Heat Island effect, and to storm water runoff concerns.  Every roof can either continue to contribute to so many of our economic and environmental concerns, or they can be adjusted to begin reversing the damage.  While vegetated roofs do not make sense for all buildings, for those they adorn the benefits to the facility operations, the building occupants, and the surrounding city are instantly evident and deeply inspiring for the people who are fortunate enough to view them.

About the Author

Elizabeth Hart CDT GRP, received her B.S. in Sustainable Development and Biology, with a concentration in phyto-remediation (the use of green plants to clean toxic waste sites).  She is practiced in various methods of sustainable agriculture, especially urban agriculture, to create infrastructure for cities to being to support themselves. Elizabeth is a founding member of Portland, Oregon’s GRiT (Green Roof info Think-tank), devoted to re-vegetating urban areas and reaping all the benefits to the environment, economy and society that come with it.

She is currently the Sustainable Technologies Specialist for the western division of an international roofing manufacturer, and is experienced in all phases of vegetated roofing – from the conceptual design, specification and procurement, through installation, maintenance and repair.  She works with architects, landscape designers, contractors and building owners to be sure each unique vegetated roofing system will function as intended.  Her green roof projects include hospital and medical office buildings, K-12 and higher education facilities, municipal, private and residential buildings - and each one makes a difference to the building occupants, community and greater environment!  
Elizabeth can be reached at ehart@tremcoinc.com