Building a green roof with flagstones and ground cover
Hi there, I live in Washington, DC and would like to install a green rooftop on the 4th story of my house which is fully exposed. I am having my deck rebuilt on the rooftop and I would like to install (instead of deck boards) some sort of material that can hold soil and plants, to make a green roof of sorts. I’d like to be able to walk on these plants and I assume they would be some sort of drought resistant succulents, but I’m not exactly sure. Can you suggest for me the best process I can recommend to my carpenter to have him construct something that will be 1) effective with minimal maintenance and 2) will last a long time ? I need to tell him exactly how to build the structure to hold the soil / plants so any information you provide me would be wonderful. Thanks. Best, Kevin W
District of Columbia County District of Columbia
Given the importance of proper design with regards to materials choice, structure weight ratings, moisture control, and plant selection based on substrate depth, we suggest you find a landscape architect or firm with green roof experience to work with, as this is a niche and very specialized field and not our area of expertise. D.C. encourages green roof use and likely has multiple firms/individuals serving the area from the city as well as VA and MD. Here is one search page from the Landscape Contractors Association where you can select a "green roof" specialty area in the search criteria: https://www.lcamddcva.org/search/custom.asp?id=3812. Here too there is an options for "green or vegetated roof" from the Chesapeake Bay Landscape Professional directory search page: https://certified.cblpro.org/
A number of groundcovers do not tolerate regular foot traffic well, including the more fragile succulents. That said, you can ask for a design that incorporates either walkable groundcovers (if suitable) or an unplanted pathway through the beds. This will also limit soil/media compaction which is a detriment to root health.