The green roof build continues, albeit slower than anticipated, but I’ll soon be happy — the permits and rebate application should be done shortly.
The underlying roof is now complete; Roof Solutions finished in 1½ days. Because my roof historically had an odd slope on one edge, I requested higher side edging, and we then ensured water drained correctly and that there were no leaks. The roof is now ready for the green portion (i.e., the drainage, irrigation, growing medium and plants), which also should only take one or two days to install.
It’s the paperwork leading up to the green roof installation that has been slower than projected. My part of the permit and rebate applications has been simple — I provided my address, a basic roof description, the reason why I want a green roof and a copy of a surveyor’s plat. I also just signed a maintenance agreement.
However, DC Greenworks, the nonprofit building the green portion of the roof, has a lot to do on their end. Andrew Benenati, the project manager, compiles 15 pages of documentation for the District permit and 47 pages for the District Department of the Environment rebate (administered through the Anacostia Watershed Society). The latter includes the structural engineer’s report, roof slope and square footage, “before” photos, materials description (e.g., composition of growing medium, plant list), detailed construction methods, permits, maintenance protocol and proposed water access. At this point I appreciate hiring green roof professionals.
Unfortunately, Andrew not only does the paperwork, but he also leads the actual installations, and late spring is very hectic. DC Greenworks tries to build green roofs before summer so that plants can become established before the heat sets in. Because the total square footage of green roofs installed has doubled since 2010 — both in the District and in North America — DC Greenworks was one busy company in May and June.
Andrew spent 10- to 12-hour days constructing green roofs three to four days a week, and this held up communication, scheduling and paperwork, pushing my installation to the end of June.
Then, an unanticipated schedule change on a massive federal project — DC Greenwork’s largest green roof installation (15,000 square feet) — caused Andrew to spend over a week in the field, stalling the permit and rebate applications for my 150 square-foot roof.
Andrew’s now mostly finished with that project, and he has sent in my rebate application and is working on the permits. If all goes well, we will install in two weeks.
Unfortunately, we’re now planting in mid-summer, which is not ideal, but frankly it can’t get any hotter than it has been already, right? Luckily, most sedum species are drought-tolerant and usually can survive summer heat. Also, my system will include irrigation piping (for less than $100) meant to help new plants during extended dry periods. But a word of warning — start planning a green roof project long before summer closes in.
Plant growth remains a concern. My green roof will start with plants dispersed, and it normally takes two growing seasons for the plants to completely fill the roof. (Some, more expensive, systems can come with a sod-like covering of plants) By starting in this heat, it may take longer for the plants to start spreading, and plants are key to a functional green roof.
Plants provide cover for the growing medium. On my flat roof, the growing medium will be mostly expanded slate and shale and is unlikely to be washed or blown away; on sloped roofs, mesh and other devices help hold the medium until the plants grow.
Plants absorb water during rains and evaporate that water into the air afterward, cycling water more quickly than a plain gravel bed. This benefit differs seasonally, but an EPA report states that a green roof can keep up to 50 percent of the annual water volume from a roof out of the stormwater system, slow the speed of water, and help maintain a more uniform water temperature — which is why the District Department of the Environment and other cities are exploring green roofs as a water management tool.
And it is why the rebate application is detailed — the roof must not only hold the weight of plants, medium and water and not leak, but it must help serve the above functions. The sooner the plants establish, the sooner the roof becomes fully functional.
Maintenance is key. As part of the rebate agreement, I will follow set procedures to maintain my roof in good condition for at least two years. I’ve also agreed — with adequate notice — to provide access for any city inspection for two years and for pre-arranged public tours. First, however, I need to install the plants, and then nurture them through the hot summer.
Annette L. Olson is a Petworth homeowner who will share her experience of installing a green roof on her row house.