Still green in 2012

My green roof had a tougher winter this year – lack of snow cover meant the relatively thin soil layer heated up and cooled down a lot.  Most of the plants did very well anyway, but a couple of sedum species had more winter kill.  No dandelion taproots have yet emerged through my kitchen ceiling (this is my secret fear about the roof).  I still enjoy looking out at it every time I go by the window at the top of the stairs and seeing the yarrow and little bluestem grass peek over the parapet from the ground.

In the wider green roof world – here’s a snazzy little tool from American Rivers using Google maps to pick a roof – your own, or the local Target store, or any downtown building and (virtually) turning it green to see how it can help improve river quality and save money.  I tested it out with the roof of City Hall (which needs repair anyway) and the approximately 10,000 sf roof, if green, would save about 116,000 gallons of stormwater from reaching the river and save about $9000 in heating and cooling costs.

Although I love my little green rooflet, I’m not ready to advocate for projects like greening City Hall.  Green roofs take structural reinforcement (they’re heavy with soil and all that water) and regular maintenance (see the dandelion remark, above).  I’d like to know the scale at which green roofs make the most sense in terms of stormwater/savings vs. installation and maintenance.  Or, what proportion of roofs in an area need to be green have a significant impact on the heat island effect and stormwater management?  Would large flat roof surfaces be better green or with solar panels?  Bottom line: I’m eager to keep learning about how we reduce energy costs, improve water quality and use all that rooftop real estate to help…