Tuesday, April 26, 2011

Green Roof Irrigation, Where are the April Showers?

Much of Florida has a unique climate, one needing to be understood for successful green roof design.

April is supposed to bring rainfall so we can have May flowers, right?  Maybe it is due to cyclical weather patterns or maybe to climate change, but over the past ten years or so excluding tropical storms and hurricanes the state has been in a drought.

Much of the Southeastern US and the Caribbean has experienced similar rainfall shortages.

In areas where irrigation is restricted to certain days or prohibited all together this can mean serious potential damage to green roof and living wall plantings.

Unfortunately, without expensive treatment systems, grey water cannot be used for irrigation purposes in Florida by state mandate.  Therefore keeping green roofs and living walls irrigated can be problematic at times.
Capturing HVAC condensate for Green Roof Irrigation

Rainfall deficits aside, daily water vapor is typically quite high during these periods of drought.  High air water vapor has advantages and disadvantages though.  On a positive note, HVAC condensate can be captured and used for irrigation purposes as shown in the above photo ( the five gallon bucket is used to illustrate how much condensate accumulates).  Ten liters per day per 1000 SF, 92 SM.
Air Conditioning Condensate to be captured and reused
Though it is good to reuse condensate water from HVAC systems, always make sure there is no biocide added.

On a negative note, hot days with high humidity encourage plasmodial and fungus growth.  Though native plant species thrive with certain plasmodial and fungal interactions, other non-native landscape plants can turn to mush and die overnight (many sedum species are prone to hot weather Southern Blight effect here in Florida).

Ultimately, in areas where long periods of dry, hot , windy weather potential exists, especially during long daylight hours, the chance green roof plants will suffer are greatly increased.

Remembering photosynthesis processes in plants during design - right plant, right place - mitigates potential desiccation and drought damage.  Take advantage of all site climatic conditions during design.

Plants survive long, hot summers on their own.  As green roof designers we need to understand all aspects of light, wind, precipitation and other eco-variable conditions the green roof will be exposed to.


Max Boughner said...

Well, climate change did a number in our April showers, so green roof owners will definitely have to do the irrigation manually until the season REALLY starts changing. Try to add pebbles instead of quick-drying soil to your green roof as well, to increase humidity for plants.

Kevin Songer said...

Max - You are right - pebbles will help. Here in Florida pebbles can be an issue with building code and liability resulting from a hurricane, but they certainly help maintain water. Maybe crushed tire crumb?