Austin City Hall

Green Roofs extend roof lifetime two or three fold, add insulation to a building, create additional useable space, can be part of a city-approved storm water management technique, and in some areas qualify owners for city incentives. They also have many benefits that are typical of any living, natural system such as reducing storm water runoff, cooling ambient air, capturing air pollution and carbon dioxide, mitigating noise and glare, and creating wildlife habitat- all of which are very desirable services in Austin, Texas. (1)

  • Reduction of heat island effect – The heat island effect is the difference in temperature between urban areas and the surrounding countryside caused by a lack of vegetation and a large number of reflective surfaces that absorb heat. The Wildflower Center research shows that green roofs can be up to 80 degrees cooler than adjacent buildings with traditional roofs. (2)
  • Reduction of storm water and pollutants – Green roofs retain and filter storm water through vegetation. In areas where rainfall contains significant pollution loads, green roofs should be able to improve the water quality of the storm water. Green roofs also help air quality by filtering pollutants from the air while adding oxygen to our urban environments. (2)
  • Increased energy efficiency of building – The cooling and shading properties of a green roof can decrease the amount of heat flowing into a building and can significantly reduce air conditioning requirements.  (2)
  • Wildlife habitat – Particularly in urban areas, green roofs can create valuable habitat for many different animals. (2)
  • Aesthetic Value – Green roofs convert typically wasted space into valuable aesthetic and recreational amenities. (2)
  • Longer lifespan – Plants and other layers on the green roof help protect the roof membrane from extreme temperatures, hail, foot traffic, and direct sunlight. This can prolong the life expectancy of the roof. The initial cost of installing a green roof, which is higher than traditional roof systems, can be partially offset by reduced roof replacement costs in the long run. (2)

               The city of Portland, Oregon offers several incentives to install a green roof. The city’s Grey to Green Initiative Program gives grants of $5 per square foot on new green roofs. Starting in late 2006, homeowners and building owners were eligible for a maximum 35% discount on their municipal storm water fee for qualifying green roofs). Projects that install green roofs in the Central City Plan District are eligible for a floor area ratio bonus, which increases the building’s allowable area, and can use green roofs to conform to the Central City Design Guidelines. Green roofs are also a means to comply with the City’s Storm Water Management Manual that applies to all new and redevelopment projects. (1)

               The question is what green roofs qualify for certain incentives here in Austin so that the city may also offer a green roof program similar to Portland’s.

"Biggest Green Roof in Texas"

Austin is currently trying to develop a specific policy which will allow for incentives. The city is working with architects, ecologists, roof consultants, and the wildflower center.

Some questions that have arisen are:

  • How much potential do green roofs have in Austin and what can potentially be accomplished?
  • What certainties would be beneficial to have for green roofs?

What we do know about green roofs in Austin is:

  • Texas is located in the subtropics region where flash floods occur often. Green roofs would be great for water (storm water) regulation here in Texas.
  • We need to alter existing technologies to cope with lots of rain at once; since this is typical Austin climate.
  • Green roofs need to become carbon sinks, not sources.
  • During Texas drought conditions water from AC units can be used to water green roofs.
  • Green roofs can be ‘irrigated’ without water, but with the addition of shade.
  • Some recycled materials in roofs are not good for green roofs because they leech out undesirable elements.

               Green roofs should be as well understood as detention ponds. We need more certainty in maintenance. We need to know that green roofs will function for 25 years. In order for these questions to be answered we must create a recipe of plants in which phosphorus and nitrogen are controlled in the nutrient poor limestone soil of Texas. We need to set up guidelines, a how-to for green roofs a home owner can understand. More research needs to be done comparing green roof benefits to white roofs and conventional roofs in regards to maintenance and containment of pollutants. (3)

               Growers (Green Roofs: working Expertise, Regional Solutions) group is currently working on a project called Green Roofs Over Austin. The project is designed to increase our local knowledge of green roofs therefore helping to develop the best practices for green roofs in Austin. The goal is to construct a wide range of green roofs throughout the Austin area. The idea is to help with design guidance, practical advice, and logistical help thereby creating a successful green roof we may observe and learn from in various settings. People interested in building a green roof should contact the growers group for more information. (4)

               Green roofs vary so much in their design and performance; they must be designed according to specific goals rather than relying on assumed intrinsic attributes. Austinites should prepare for a period of trial and error before any incentives come along. We must perfect the Austin green roof before we reward anyone’s green roof attempts. We must assure ourselves that incentives are given to those deserving!

Sources:

1)      http://www.portlandonline.com/osd/index.cfm?a=114728&c=42113

2)      http://www.wildflower.org/greenroof/

3)      Simmons, Mark T, et al. Green roofs are not created equal: the hydrologic and
     thermal performance of six diffeerent extensive green roofs and reflective
     and non-relfective roofs in a sub-tropical climate (July 2008). Print.

4)      http://www.growersaustin.com/

5) Photos courtesy of Raymon Serna

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  1. I totally agree that we should perfect the green roof before Austin hands out incentive money or grants. You don’t want to give out money if it is going to backfire 5 years down the road or cause more damage and needs more money to fix problems it created. If Austin was to have something similar to Portland incentive program, they might want to consider regulations of what material they can use or certain specs that have to be met. I think the best way is to look at successful green roofs all over the world.

    On your last bullet point you mentioned that some recycled materials might be harmful, I am just curious by what you meant in this statement? Did you mean that using recycled plastics in the liner or using recycled contaminated soils, what is the material being recycled? I am also confused at how water from AC units to be used to water green roofs in drought conditions. Are you suggesting that if the plants on the roof need irrigation the best way is to use already existing water sources on the roof, such as AC units?

    I also totally agree with wanting the roofs to last for at least 25 years and the need more certainty in maintenance but don’t know if we have 25 years to do research. I think it is a learning process and a new market and can potentially create new jobs [1]. Also the EPA made a new technical guide to help federal agencies minimize the impact storm-water runoff of federal development projects on nearby water bodies, issued on December 10, 2009 [1].

    In the third to last paragraph are you suggesting that here in Austin, we only use native plants that do well in nutrient poor soils? What if you still used native plants that are drought resistant but import topsoil that is more fertile? If you use non-native plants these can become invasive and become a problem for agriculture and out compete native species of plants. I also think that there should be regulations on pesticides and harmful chemicals that could still diffuse through soil and get into ground water through rain runoff. The USGS is doing a lot of research in this area and over time several pesticides have collected in our drinking water and given more time could potentially become more harmful [2].

    I think green roofs have a lot of potential and think it would be great to have a working landscape on top of buildings. Maybe one day in the future, sky scrapers, business buildings, and residential buildings will all have green roofs and planter boxes along the windows.

    [1] http://www.greenroofs.com/
    [2] http://toxics.usgs.gov/topics/sw_contamtransport.html

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