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'Green Roofs' Face Building Code Barriers

Sustainable roofing practices are spreading throughout the United States and across the world with local and state governments recognizing their benefits and incentivizing their implementation, yet Florida's infrastructure lags behind because the building commission does not recognize them as a best management practice (BMP).

Sustainable roofs, or green roofs, are essentially roofs that are covered, or mostly covered, with a garden that is layered with soils, insulation and a waterproofing component so the water doesn't soak into the ceiling.

Glenn Acomb, a senior lecturer in landscape architecture at the University of Florida, has done extensive research on green roofs and their benefits both environmentally and structurally.

Despite their many benefits, however, Florida has been reluctant to include green roofs in its building code, making it more difficult to implement them on a large scale.

The building code is a highly debated set of rules for building design, usually supported by research that is meant to protect the health and welfare of citizens and infrastructure, Acomb said.

Acomb said the Florida Building Code’s particular concern in the case of green roofs is their performance in hurricanes or other natural catastrophes.

“The important research question is of vulnerability,” Acomb said.

Acomb and his colleagues received a research grant from Federal Emergency Management Agency in 2012 to test these vulnerabilities, and their findings yielded positive information in the case for green roofs in Florida.

In conjunction with the UF College of Engineering, Acomb and his colleagues tested green roofs in a wind simulator and found that the plants and their roots mostly held up in hurricane-force winds of up to 120 mph. They also found that built-in-place green roofs performed better than modular tray green roofs in the wind uplift trials.

Acomb said the Florida Building Code didn’t accept the research as sufficient for recognition, because it wanted to ensure stability for speeds up to 160 mph.

"I think we've provided some very reasonable information, they're just not ready to make a risky decision to embrace them," Acomb said.

Chelsea Eagle, the director of communications for the Florida Department of Business and Professional Regulation did not comment on whether the barriers to implementation were political, but instead referred to specific code requirements that vegetative roofs must meet in order to be implemented, as well as the need to conform to the Florida Fire Prevention Code.

The code requirements Eagle cited involved concerns with structural fire resistance, occupiable roof areas and the weight of landscaping materials. However, it did not address the lack of recognition in the code for the benefits of vegetative roofs.

Marie Kurz, Ph.D., a scientist at the Helmholtz Centre for Environmental Research - UFZ, Germany, said the two biggest threats to Florida’s water supply are over-pumping and contamination.

Acomb said that with green roofs, this water would instead be absorbed and utilized by the plants, ultimately cycling the water naturally.

Stormwater runoff from rooftops is a major contributor to groundwater contamination, especially in urban areas, Acomb said.

According to the Florida Department of Environmental Protection, Florida withdraws more than 4 billion gallons of water a day from the aquifer to satisfy the demands of people, agriculture and industry, ultimately impacting the flow and water levels in the aquifer and springs.

The biggest contaminants to Florida’s water supply are nitrates, Kurz said, which make their way into groundwater via pesticides and fertilizers that get picked up by rainwater and absorbed into the ground.

“The key is to educate people about their water and where it goes,” Kurz said.

Aside from water conservation, green roofs also lead to a longer lifespan for roof materials by increasing the thermal performance of the roof, Acomb said. In a typical Florida summer, rooftop temperatures will experience extreme shock as they transition from around 70 degrees at night to as high as 140 degrees during the day, ultimately damaging the roof materials.

With green roofs, this temperature jump is much less dramatic, from around 75 degrees to 100 degrees, making the materials last longer and creating a thermal barrier that conserves some energy.

Longer-lasting materials and energy conservation means a reduction in costs. Acomb said green roofs typically reduce costs by about 10 percent.

Green roofs also play a role in absorbing carbon dioxide, reducing greenhouse gases and improving air quality, according to a study by the Natural Resource Defense Council.

In Germany, buildings with green roofs are actually insured for a longer time (40 years as opposed to 30) than buildings without them, because the insurance companies recognize that the buildings will last longer, Acomb said. However, because the Florida Building Code does not recognize green roofs, they will typically not be insured at all.

Green roofs are commonly accepted as BMP in northern climates, but there is a lack of research on their use in a subtropical climate like that of Florida which is prone to hurricanes and higher precipitation rates.

According to the Florida Building Code's website, the Florida Building Commission is now accepting proposals for modifications to building code for its new edition, which will be implemented in 2017. Acomb said he hopes the efforts he and his colleagues have made will help spur change in the building code.

“I believe that Florida will eventually embrace green roofs,” Acomb said. “It’s just a very slow process.”

Jake is a reporter who can be contacted by calling 352-392-6397 or emailing news@wuft.org.