Okay, my green roof has been built on my front porch.  In the final task associated with it, the Anacostia Watershed Society (AWS) came out to verify the green roof’s final dimensions before processing the District Department of the Environment (DDOE) $750 rebate, which I will receive within six weeks. 

The new green roof on the front porch of Annette L. Olson's Petworth home. (Photo by Annette L. Olson)

I want to say thanks to DC Greenworks, Roof Solutions, AWS, the structural engineer and DDOE for helping make it happen.  It’s nice to get up in the morning, look out the window like I always do, and see plants, some of which have already grown half an inch!

Of course, now I get to take care of the roof.  DC Greenworks normally provides maintenance the first year, but I agreed to do it to keep costs down.  Besides personally wanting to keep it nice looking and functional, in order to receive the DDOE rebate, I had agreed to ensure “80 percent vegetative coverage and continued stormwater management performance in perpetuity.”

Well, achieving 80 percent will take some attention — right now the little plants cover less than 10 percent of the roof.  DC Greenworks says it’ll be two growing seasons before they’ll cover it.  

As for “in perpetuity,” I checked with AWS, and the perpetuity part is within reason.  I have agreed to make my place available for inspection for two years, and to replace plants and other materials as needed. But if in 10 years, for instance, the entire roof needs to be replaced, I don’t have to build a green roof again.  I don’t plan on moving or selling this place, however, and my goal is perpetual green anyway.

So DC Greenworks created a detailed five-page maintenance plan, which outlines the following steps:

●Weed every two weeks this summer. Mulch helps keep invading plants out, but weeding this often gets invaders before their roots get deep, making weeding easier overall). Also I should water every few days (via the timed sprinkler) if there is no rain.

●Continue biweekly weeding in the fall. Leaves should be raked and any large, unsightly seed heads cut off to prevent future shading of the plants. The plants should be watered once a month if there’s been less than an inch of rain.

●Do not let snow pile in any one place during the winter.  If it’s warm, the area should occasionally be weeded.  Otherwise, I should stay off the roof if there’s ice. 

●In the spring, send soil samples out to test nutrients and acidity three weeks before early flowers like daffodils bloom.  Acidic soils can damage the filter and other fabrics in the roof and the plants. Acidity is rare, but if it becomes an issue, lime should be applied.  If nutrients are low, a slow-release fertilizer (already provided by DC Greenworks) should be applied.  Also, drainage should be checked, debris should be removed and biweekly weeding started again.  The plants should be watered if it rains less than one inch a month. 

An example of the goal for plant coverage on a modular green roof installed in Northeast Washington in 2011. (Photo by Andrew Benenati)

There are also how-to suggestions like don’t use chemicals for weeding (prevents downstream pollution), and don’t use a sharp weed tool (the waterproofing membrane is only 4 inches down).  My personal favorite:  Don’t use a flame-based weed torch.  I agree — not near my house.  

The one thing the plan doesn’t have is how to fend off D.C. squirrels.  So far, they haven’t touched the roof.  But I expect my neighborhood squirrels to be very busy burying and digging up nuts fall through spring.  DC Greenworks says that squirrels haven’t been an issue with other roofs; if someone knows otherwise, please let me know.

So I am set and will soon be out there weeding and watering my porch roof.   My neighbors now know what the green roof is all about, and seven on my block have come over to look at the roof from my bedroom window.  They liked it a lot and asked lots of questions.  Everyone has been supportive.

The view from the street of the green roof on Annette L. Olson's Petworth home. (Photo by Annette L. Olson)

So thank you for reading about my experiment in green roofing.  If you want more information, I would first check out DC Greenworks and Green Roofs for Healthy Cities.  For how to build green roofs in D.C., see the DDOE green roof Web site, especially the Green Roof Toolkit.   Cheers.

Read more about Annette L. Olson’s green roof installation

Annette L. Olson is a Petworth homeowner who has been sharing her experience installing a green roof on her rowhouse.