Tabard Inn’s Green Roof:
Downtown Garden for Edibles and Roses

by Guest Blogger Sarah Murphy of Canopy  (This guest post, while technier than what’s normal for this blog, contains info that I think is both cool and blog-worthy.  And no, they’re not paying me or promising to link to me in exchange.) 

For over 25 years the Tabard Inn, near Dupont Circle, has attracted Washingtonians and visitors alike for its garden courtyard, quirky interior and amazing food fare. The menu changes with the season with a majority of the food coming from the Tabard Inn’s nearby farm. Always interested in staying ahead of trends, Irene Mayer, the Inn’s in-house designer, started looking into putting vegetation on their numerous roofs in 2007. She approached Canopy, a company that specializes in restoring the urban canopy through green roofs and city gardens, about incorporating green roofs onto their buildings. 

The Inn had decided to add a small roof over their outdoor serving area, and asked Canopy if it was feasible to put an herb garden green roof on it.  Canopy suggested building the roof to be strong enough to hold the 12-18 inches necessary to support the specialty herbs. They also installed a skylight hatch with a pull-down ladder to simplify the short trip from the kitchen to the rooftop.  A hose bib was also added for water access. 

Once the roof installation was complete, an EPDM membrane was applied. EPDM is a common waterproofing membrane that stands for ethylene propylene diene M-class rubber.  Next, Canopy installed a root barrier made of high-density polyethelene. To create the look of a traditional herb garden, Canopy constructed numerous wooden boxes out of rot-resistant cedar in varying depths to accommodate a variety of herbs and other herbaceous plants.  Each of the wooden boxes was filled with a specially blended growth medium comprised of 60% lightweight aggregate, 10% aggregate fines, and 30% organic matter.

The 150 square foot roof was then planted with Lemon verbena, 2 varieties of bush blueberry, rosemary, chives, thyme, sage, annual basil, and 2 varieties of climbing roses.  The roses were requested by The Tabard’s owner, Jeremiah Cohen, who has an office that overlooks the new roof top herb garden.

Overwhelmingly pleased with the roof top herb garden, the Tabard approached Canopy again in the spring of 2008 to 2 create more green roofs on roofs in need of new waterproofing.  Canopy eagerly accepted the new projects, but there were a few challenges along the way. 

The first challenge with the new roofs was that they both have a 5/12 pitch, meaning each roof is angled nearly 45%.  Erosion and soil slumping become an issue at only a 2/12 pitch, so Canopy had to utilize special materials to prevent any soil slipping off of the deeply pitched roofs.  They decided to employ a technique used by German Manufactures at Optigrun, plastic “bananas” that latch onto a geo-textile mat also installed on the roof. 

The plastic “bananas” are approximately 2 inches deep, so they hold 2 inches of soil in place while they also have spikes emerging from them that hold pre-vegetated mats in place.  The mats, similar to sod, were grown at a nursery in Stevensburg, Virginia with a variety of sedums.

The installation of the soil and pre-vegetated mats was a slow and laborious task exacerbated by the fact that the restaurant wanted to stay open for outdoor dining.  Canopy coordinated the installation between meals.  The roughly 350 square foot installation took about 2 weeks total.

Now the 3 green roofs offer verdant view for guests.  Additionally,  the green roofs are offering insulation benefits, reducing energy bills and helping reduce storm water run off.  The kitchen has also noted a reduced need to by expensive specialty herbs.