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.
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!
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.
5) Photos courtesy of Raymon Serna