Exciting Rooftop Gardens

Dawn Szelc LDG Secretary, Clear Blue Landscapes

​The Landscape Designers Group met at the McLean Community Center to hear two designers talk about their recent projects with rooftop gardens. 

​Lan Hogue from Michael Vergason Landscape Architects spoke about the City Ridge project https://www.vergason.net/city-ridge , a 10-acre mixed use development on the former Fannie Mae campus on Wisconsin Ave in Washington, D.C. The new owner, a Japanese firm Sekisui House, removed some of the newer buildings on the property but retained the oldest building as a historic site. The area features residential and retail properties as well as outdoor public spaces and underground parking. It was designated as a Leed Gold Public Space, which includes rainwater harvesting, bioretention, and the green roof which Lan worked on. 

​Lan described the green roofs that she worked on which were essentially over the parking garage that was developed under the site. They were planted with a “high mow” mix of fescue and other perennials. The mix was 60% hard fescue, 20% creeping fescue, and 20% red fescue. The “high mow” term means that it should be left to grow fairly high, so only mowing once per year. That is not what the maintenance personnel allowed to happen, so she has had to educate the people on how to maintain the garden as intended. There was an area with a 45-degree slope which required the use of a structure to hold the soil and plants. One area tended to be used for construction traffic and had become very compacted so had to be redone as the plants were not growing well.  There was a discussion during the meeting about the best native grass to use on such a site, and one member offered that native Carex is a good choice. It can handle shade, flops over nicely and develops into a nicely filled area.
Lan also discussed the three heritage trees, Pin Oak and Willow Oak, which were growing on the site, and were painstakingly relocated onsite by a tree moving company. She also commented on the value of a product called Instant Hedge from Oregon. They provide  mature hedges conveniently packaged for installation. 

​The second speaker was Tomi Landis, from Landis Architects, who presented a residential rooftop garden in Washington DC. The garden consisted of different spaces including an outdoor kitchen, seating area, and contemporary water feature. All the elements had to be carried to the roof using a crane situated on the street in a specific time frame dictated by the city. Permitting was difficult because the garden was not allowed to be seen from the street. Additional visual barriers were used in certain directions. 

She found that the water feature had a lovely sound but created too much splash so that needed some adjustments.  The lighting was designed and installed by our own Olsen-Weaver lighting, and the irrigation was completed by Outdoor Illumination. There were numerous planters used with polystyrene peanuts at the bottom and a soil mix consisting of soil, sand, and compost. These were from the Jay Scotts Collection as well as custom built.  The plants were installed by Great American Landscapes, with annuals by Julie Friedman, another LDG member. The garden elements were installed upon a new deck which used Moisture Shield composite decking material which is marketed as 33% cooler than other completing composites. There was a large umbrella over the seating area which caught the audience’s eye. Tomi said this was from Treasure Garden. It was 16 ft across and weighed 200 lbs. but was very easy to move around. She thought that the catalog company, Frontgate, had similar types of umbrellas. For some additional photos and gallery of work see the link.
https://www.landisconstruction.com/our-portfolio/downtown-dc-roof-deck/