SandyLoam's blog

Everyone’s been talking about green roofs, not the kind with solar panels, but a true, living planted green roof.  Chicago is bursting with them, and now New York has passed a tax break to encourage New York City residents to think green when it comes time to put on a new roof.  The storm water retention qualities alone were enough to rate a $4.50/ft2 tax credit that New Yorkers can apply toward the cost of their roofing project.

So let’s say you have a roof that needs to be replaced or, or you’re just ready to take some climate change repair into your own hands and go green.  What does a green roof entail, and how do you turn a formerly typical (and usually really unattractive) rooftop into a planted landscape that help clean the air, cool the city, and become home to butterflies and bees?  Here’s how a fairly typical installation went this September in the Tribeca area of NYC.

The site was a five story former medical building that had been converted into a co-op.  At some point in the building’s history a smaller 6th floor had been placed on the roof, built so that the unit had access to two sides of the roof of the 5th floor.  One side of the roof was built out in a more conventional NY style, with wooden floor tiles, lots of raised planters and a shade pergola above a dining table.

The other side of the roof, comprising roughly 900ft2, was left bare.  When the co-op need to re-roof the building two years ago, the bare area was resurfaced, but still remained an eyesore, especially when compared to the landscaped roof deck out the other side of the unit. 

Eventually the owner decided it was time to take a look at the possibility of a green roof, not only for its aesthetic qualities (since the view out of one set of glass sliding doors was nothing but a rubberized roof surface) but also it’s environmental impact.  Greensulate, a NY based green roof and wall firm, was brought in to discuss, design, and install the green roof.

Once the initial measurements were taken, the next steps were to have a building engineer calculate the roof’s weight capacity, and then talk with the roofing company who had recently installed the new surface to ensure that the proper green roof was put down on top in a way that would maintain the integrity of the waterproof surface.

Greensulate worked with the client to design a primarily extensive green roof, with a few raised areas to give the space some variance and texture, and allow for a wider variety of plants.  There would also be several visual rivers, created with the same river rock that would provide a border for the green roof, and surround any penetrations (vents, skylights, etc.) to keep their edges plant-free.

Once a final plan was agreed upon, it was time to start ordering plants and materials, and begin the coordination of what would be a two-day installation.  Before day one actually started, the drainage and root barrier layers would need to be ordered as would 6 tons of planting medium, 3 tons of river rock, and over 250 plants.

Working with nurseries in New York and Connecticut, all the plant, soil, and stone materials were ordered for delivery directly to the site on day one, or to be picked up the day before the installation by Greensulate. 

Day 1

Arriving at 6:30, Greensulate staff arrived to begin offloading plants and planting medium outside the Tribeca building. 

Getting materials up five stories usually involves a large freight elevator, or a crane.  In this case, there was no freight elevator, so a truck with a boom crane was brought in and parked in front of the building.  Greensulate had staff on the ground and on the roof to quickly distribute the materials across the roof as they were craned up.  First came the rolls of drainage layer and root barrier, which were cut and laid across the entire roof.  Then came the bags of river rock, which were spread along the entire border of the roof and around all roof penetrations.  Next came the planting medium, in large 1-ton capacity super sacks which could then be emptied directly onto the drainage/root barrier layer.

Greensulate staff then proceeded to spread the planting medium to a fairly uniform depth of 3 inches.  In certain areas, Greensulate created berms, or raised hilly areas in which some of the larger plants would be set.  Care was taken to make sure all of the drainage material was covered and that the river rock borders and visual rivers concealed the underlying layers.

Once the planting medium was prepared to the design’s specifications, plants could be brought up (this time over a number of trips in the building’s main elevator) and set (still in their containers) according to the planting design.  This step helps confirm in 3D what had only been visualized on paper during the design process.  Seeing the plants laid out, but not yet set in the ground helped confirm that they would look well placed, but also perform their functions in the cases where a plant would be blocking an ugly view from inside the client’s home.  By walking around and looking at various viewpoints, Greensulate staff could adjust placement here and there as needed.

Once all the plants were in their final positions, it was time to call it a day.  All that was left for day 2 would be to plant the roof, and water it in.

Day 2

The plants for this roof were chosen for their hardiness in a green roof setting (wind, sun, low water conditions) and for their ability to bring different colors, both foliage and blooms, during different times of year.  The were as large as Panicum grass in 2-gallon containers, and as small as a plug of sedum in 72-plug flats.  Varieties included native grasses, hyssop, lavender, allium, and seven varieties of sedum.

Planting started at 9:00am and continued to 3:00.  Plants were taken out of their containers and set into the ground where they had been placed on day 1.  Planting sedum plugs is a bit time consuming, but in order for them to form a healthy, solid mat in a short amount of time, 5-6 plugs were planted per each ft2. 

As the green roof took shape, it was clear that the planting design was accomplishing the goals set out—beautify the roof, block ugly views, and create a green habitat in Tribeca.  Much to the delight of the Greensulate staff, even before the last plant was in the ground, the entire green roof was alive with butterflies, and honey-and bumblebees.  It had taken them less than 24 hours to discover a new source of food in Manhattan.

Once the last plant was in place, it was time to give the entire roof a good dose of water, to start getting the plants established in their new home.  As with many of the green roofs that Greensulate installs, this roof had no irrigation system and would primarily rely on rainfall to survive.  It would be watered several times a week after installation (unless there was rain) to ensure the plants got acclimated, but in successive years only in very dry periods would supplemental watering be necessary.  Even then, this water would come from four specialized water tanks that would collect rainwater to be used later, keeping this green roof independent from an irrigation system.

At the end of day 2, the green roof was complete.  The client had a new, beautiful view shed, as did the people in the taller buildings surrounding it.  New York City was one roof closer to preventing storm water overflows, and the butterflies of Manhattan had a new place to call home.