A Petworth homeowner’s green roof one year later

August 14, 2013

Last year I installed a green roof (a roof with soil and plants) over my front porch and wrote about the process in the Where We Live blog of The Washington Post.   I was excited about installing a green roof but also had some concerns, as did some of the commenters to the blog.  So, one year later, here is an update on how it is faring:


(Photo by Annette L. Olson) The green roof on Annette L. Olson’s Petworth home is in full bloom in the spring.

It is freakin’ beautiful, and I am very happy with it.

Because it has been a wet summer, I haven’t had to water it in the last 11 months. Every one to two weeks I pull up about five to 10 little weeds, but there are fewer each week. It’s been entirely worth it.

To review, last year my front porch leaked, and I needed a new roof.  Because my bedroom windows look directly onto the roof’s asphalt shingles, I started thinking about a green roof/garden, which has a number of environmental benefits such as insulation, stormwater control, pollution retention, reducing the heat island effect and more (see previous posts).

I checked into it, got excited, started blogging, and then became frustrated over the expense. My roof would be one-third more expensive than a regular roof, partly because it had to be restructured to withstand the new weight.  Also, my roof would be one of the smallest that my installer, DC Greenworks, had constructed; larger would have been cheaper on a square foot basis.  However, the District’s Department of the Environment (DDOE) rebate via the Anacostia Watershed Society (AWS) would help with about 10 percent of my total cost.  Because the environmental benefits still appealed to me, along with a much better view, I went for it.

Now, one year later, the porch roof has been solid. The plants (a mix of sedums) have mostly filled in the space, and they bloomed beautifully in the spring.  A variety of bees and butterflies have been hanging out, along with midges, a ladybug, and two trapdoor spiders.  Last fall, a giant praying mantis took up residence.  Amazingly, no squirrels have disturbed the roof (I’m just floored by that), but birds occasionally will hunt for insects on it.

My cat loves sitting in the window, and the garden is the first thing I look at in the morning.

My neighbors also seem to appreciate the greenery.  My next door neighbor Mel asks how the “marijuana/weed” is growing up there. Ha, ha, he’s just kidding. Now that the sedums are visible from the street, a few neighbors ask me how the roof is doing or even tell me it looks great.  No neighbors have complained. Instead, when I’ve given tours, I have even gotten some oohs and aahs.


(Photo by Annette L. Olson) The green roof is barely visible on Annette L. Olson’s Petworth home.

Admittedly, no one on my block is rushing to build a green roof, but two others were built within walking distance of my house last year.  And, according to an industry survey, the greater D.C. metro region again led the nation in green roof planning in 2012; with an estimated 1.2 million square feet of public and private green roofs constructed or scheduled for construction, an increase of 50 percent from 2011.  However, some of that square footage is for projects that are scheduled but not yet installed, according to Peter Ensign, the executive director of DC Greenworks.

Some common green roof benefits, such as insulation, do not apply since my roof is over a porch and because my roof is small.  Still, it is clear that the construction helps the environment. My green roof supports living things, something an asphalt roof certainly cannot do, and its 150-square-foot span retains water when it rains (AWS calculated 2,400 gallons of stormwater annually).

Combined with my rain barrel and rain garden, it helps absorb the water that normally would run off my property and thus does its part to help the District control stormwater issues, such as flooding and sewer overflow into the Potomac that result from all the hard surfaces in the city.  With more roofs, barrels and gardens being installed throughout the District, flooding in certain neighborhoods may someday be less.

On a related note, I just received an e-mail from DDOE that, in cooperation with DC Water, it is starting to discount water bills for green roofs, rain barrels and other water control measures.  Last year, I was told that green roofs did not qualify for a discount, but DDOE’s new RiverSmart Rewards Program is now taking effect and green roofs are included.   Depending on how I manage my stormwater, I can save up to 55 percent of the DDOE stormwater fee, and up to 4 percent on DC Water’s Clean Rivers Impervious Surface Area Charge (IAC).  These fees are around $13 a month for me (a 30 percent increase from last year), and they will continue to rise.  However, I may wait to apply so I can use the DDOE’s “Simplified Application” form meant for owners of small properties, which comes out in 2014; the discount for the stormwater fee (but not the IAC) is retroactive to May 2009 or date of installation.

By the way, owners of large properties can also generate Stormwater Retention Credits (SRCs) that can be sold privately.

So that is the latest on my green roof.  We’ll see what next year brings.  Researchers are searching for more effective, native plants to replace sedums, so I may introduce those, as well as some shallow-rooted herbs. It’d be cool to support even more pollinators — and to provide a home for another praying mantis.

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Dion Haynes | August 13, 2013