by Jonah Goodman
guest contributor

When my wife and I were looking for homes in the area way back when, a garage wasn’t a high priority on our list. When we found the house we wanted it just happened to come with a 3-car garage. It was something our one-car household didn’t need but the extra storage and later covered play space grew on us.

One challenge with the large covered space was our entire backyard was impermeable. Our 20’x37’ garage would send a lot of rain water down to our basement door. Managing that rain runoff and basement flooding was a constant issue. Recently the older garage roof started leaking and rotting some of our joists. Repairs and replacement of the roof were going to have to happen sooner than later.

We had heard of green roofs and liked the eco-friendly aspects of it. But the ability to manage the water runoff and absorb it after storms seemed like a great solution. For a few years I reached out to companies that grew green roof plants, architects and general contractors to try to figure out what it would take to install something on our garage. While there was a market for downtown buildings to install green roofs, most people weren’t sure how to do a residential project like ours. It was big enough that it required structural engineering updates but tiny compared to the downtown installations happening.

The idea was put on hold for a few years until I read the Petworth News article about Annette’s front porch green roof install. I reached out to Annette and she connected me with Peter Ensign who did her install. It turns out he knew a thing or two, having helped the District establish their green roof initiatives and DOEE’s Riversmart Homes program.

Trays of pre-grown plants ready to be installed.

Our plants were all grown at Emory Knoll Farms in southwest Virginia. They are grown in 1’x2’ trays. There is a plastic base with 3-4 inches of soil and sedum plants across the top. The plants are a mix of leafy greenery and native plants that will require limited maintenance and provide year-round greenery. The trays are held in place by a metal framing system that is attached to the garage roof. The framing means the plants won’t slide off the roof in a heavy rain or wind.

There were a few options we had during the planning. We could select the sedum variety we wanted to install. Additionally, we had the option of a fully pre-grown system or using plugs and cultivating the growth ourselves over the year. The costs were similar in the end and neither of us has a green thumb so we went with the pre-grown trays.

Installing the new green roof on the garage.

Our green roof installation was completed in June and we have been very happy with the benefits it provides. The project took a few weeks because we were having structural work done to the garage beforehand to handle the extra weight. Reinforcing the joists took about a week. The roof was replaced with a new TPO surface and that took one day. The metal framing to hold the plant trays took half of a day. Finally, the actual installation of the plants only took one and a half days. In the end it cost us about $30 per square foot for the plants and tray installation, not including the new roof and structural work.

A few good rain storms have come and gone and the plants and my basement are both happy. Beyond the rain runoff management we already can feel about a 5-10 degree decrease in the temperature inside our garage. The old flat black roof created quite the heat island, making it unbearable in the summer. After a few days the plants have perked up and they have already started flowering. This is attracting a lot of pollinators and curious birds. Hopefully, more insects and wildlife will start enjoying it.

If you have a large garage like us or a front porch like Annette’s that you could transform into a green roof, I definitely recommend it. It is an upfront investment for longer-term, greener benefits.