SL Green Realty Corp., the largest commercial landlord in New York City, is working with tenants across its NYC properties to achieve a 30-50 percent reduction in greenhouse gas emissions over 10 years. Green roofs are playing a role in the effort, including one 44 stories up at 1185 Avenue of the Americas.
The 1.1 million-square-foot commercial office building is owned and managed by SL Green, a leader in urban sustainability. Among the many environmental advantages of green roofs, they reduce the urban heat island effect, ease storm water runoff, filter pollutants in rainwater and remove carbon dioxide, a greenhouse gas, from the air. In addition, by lowering building cooling demand, they can cut greenhouse gas emissions associated with producing electricity.
The roof replacement project was completed in the fall of 2017, and key participants shared their perspectives on the project, including representatives of four companies:
- SL Green, the property owner and management company
- CANY Architecture and Engineering DPC, the construction management firm
- Nations Roof LLC, the installer
- ZinCo USA, the green roof system consultant and manufacturer
1. The Realty Management Company
Daniel Huster, Senior Project Manager, SL Green Realty Corp.
How did this project get started?
SL Green has an on-site team that manages 1185 Avenue of the Americas. I handle all the construction within the building and several others in our portfolio. The old (bituminous) roof was past its warranty. It had absorbed water, and we were showing signs of leaks in our mechanical room and the spaces below. We engaged CANY to put together a package to design and replace the roof system. They specified a reinforced waterproofing membrane from Kemper System America Inc. for the main roof, and we also asked CANY to bid with a green roof on top.
Green roofs are uncommon at such heights. What convinced SL Green?
When we originally put the RFP out for roofing renovation, we asked for the green roof as an alternative. After the group considered all the advantages and then saw the pricing, we made a collective decision that it was worthwhile to pursue.
SL Green already has two buildings in New York with green roofs — 100 Park Avenue and a vegetable garden at 1515 Broadway near Times Square. But those are setback roofs at much lower elevations. The roof at 1185 is essentially rectangular, so this was an opportunity. The floor plates spread the weight, and the green roof and pavers could cover roughly 4,500 to 5,000 square feet of the 14,200 square foot total. It took a while to work out the details on the elevation, but CANY and the green roof consultant from ZinCo figured out a design that could work.
2. The Construction Management Firm
Andrew Cucciniello, Project Manager, CANY
What was the condition of the existing roof?
The existing roof was a modified bituminous system — a torch-applied sheet on the concrete deck followed by layers of rigid insulation, topped with cover board and two more plies of the mod bit. Judging by the wear, it had been down about 20 years. We completed an investigation of the assembly, and found that it had failed in a number of locations and water had infiltrated the layers. This was one of the driving forces behind our recommendation for a full replacement aside from any repair.
What is involved with the investigation?
Typical with any investigation for us, we coordinate with an environmental consultant and an independent agent, who cuts holes into the main roof frame down to the structural deck so we can understand all the existing components. This also gives us an opportunity to do material sampling and test for asbestos-containing materials (ACMs). (There were none.)
Testing lets the demolition contractor know the extent of material removal. Also, the environmental consultant is required to submit a laboratory report and must notify the NY Department of Buildings before we can file for permits. The city wants to know there are no ACMs present, and if there are, the Department of Environmental Protection will receive notification about the abatement procedures.
What do you consider in specifying the green roof waterproofing assembly?
When we get a project like this, there are several different types of materials we can consider. We try to analyze the use of the roof and what kind of traffic it will experience in terms of mechanical equipment, people performing maintenance and repairs, etc. Also, for a protective roof assembly, there can be NY Energy Conservation Code requirements for insulation.
In this case, if we were to go with a built-up roof (BUR) it would require drainage at the surface, which would mean tapered insulation (likely a polyisocyanurate). Tapered insulation would drive our base flashing height halfway up the parapet, which we could not accommodate due to a scaffold track around the perimeter.
So we selected the liquid-applied Kemperol 2K-PUR reinforced membrane system, which is self-flashing and installs directly to the deck. Since it is a fully-adhered system that can withstand ponding water, we did not have to design for slope. A (non-tapered) rigid-styrene insulation board sits on top. Because the Kemperolmembrane is root resistant, a separate root barrier was not required. There were also ongoing discussions with Kemper System and ZinCo throughout our design process to assist with the final overburden components.
Are inspections conducted during the construction phase?
Our company performs QC inspections throughout the course of construction. From existing roof material removal and any preparation of substrates, as well as the new roof installation, flashing details, and the overburden placement. We have been involved with Kemper System for about two decades. With these roof assemblies which offer a 20-year warranty, we conduct periodic inspections with Kemper System to make sure the installation meets their warranty compliance requirements. We were the applicant of record with the NY Department of Buildings, though, and are on board until the project gets closed out.
3. The Installer
Michael Johannes, President, Nations Roof-East
Why was Nations Roof selected for this green roof rather than an architectural landscape company?
When a realty management firm first looks at us as a roofing and waterproofing company, they see our financial stability and our commitment to working safely. Nations Roof consistently ranks in the top five roofing contractors in the U.S. We are committed to delivering comprehensive roofing solutions. During any repair or construction project, we understand the need to protect employees, guests and valuable assets, and at the same time, to maintain business operations and service levels throughout the project. This project was completed working off-hours and through occupied spaces that needed to be ready for the next workday without interruption.
Also, not a lot of landscaping companies are going to carry the required levels of insurance coverage without numerous exclusions for such things as building height. We work constantly on projects from eight to 50 stories in the air installing roofing systems both on new construction and renovations such as 1185 Avenue of the Americas.
What about the quality of the waterproofing installation?
Landscape contractors are not generally authorized to install roofing and waterproofing systems. Our foreman, project managers and installers are employees and most have been with our company for years. Our crews are trained and experienced in installing leak-free systems. That includes certified training by Kemper System in the liquid-applied reinforced membrane system used on this project. Plus, ZinCo provided guidance on installing the garden components and the transitions to the interlocking paver walkways. We can supply a “finished turnkey green-roof” with all the components, and provide the owner with a warranted watertight installation.
Has Nations Roof installed other green roofs in New York City?
Actually, we’ve done many garden roof installations. For example, we successfully completed 100 Park Avenue with SL Green, which was a LEED Silver project, and Via Verde, an affordable housing complex in the Bronx.
New York and Chicago are at the front of the green roof trend. Via Verde was former N.Y. Mayor Michael Blomberg’s first initiative into green gardens back in 2010, and they caught on. Most new roof projects we do in the city now have some form of hardscape and softscape. It’s valuable space that in the past has gone unused for the owner and the tenants. If you live or work in one of these buildings, it’s nice to have a place you can go that is secure. When we go to Via Verde now, we see mothers with baby strollers sitting and reading books in what would have been just a roof a few years ago.
What do you see for the future of green roofs?
We believe the market will continue to be strong for livable roof space that improves the environment, and we will continue to be in the middle of that with big developers. It is also the commitment and leadership of property owners like SL Green to invest in these initiatives that will continue to drive success.
4. Green Roof System Consultant and Manufacturer
Nick Smith, National Account Manager, ZinCo USA
What are the primary issues with installing a green roof at this height?
Any green roof installed at 500 feet can invite potential problems with horticulture, erosion and exposure. Let’s focus on those three: To analyze exposure, we recommend a wind study and sun/shade study, and CANY performed these tests.
Wind uplift is a major issue with the physical properties of the green roof. We are concerned with getting the proper ballast. In this situation, a standard engineered-material assembly would not be heavy enough to protect against a worst-case scenario. The solution was to add significant weight to the assembly within the cups and the drainage elements. The engineered growing media is also a bit heavier than normal.
Wind scour, a horticultural issue, is the plant’s ability to stay vital with continuous wind. We know after looking at hundreds of studies that trouble spots most often occur around the perimeter and at corners, where you get microcurrents of fast-moving or swirling air. The conventional wisdom is that on a building over 500 feet tall that is going to withstand serious wind 24 hours a day, plants simply won’t grow at the perimeter and corners.
To combat erosion, we separated the vegetated area from the walkway deck in many areas with an aluminum angled-edge. The aluminum barrier acts as a separation for the way the wind moves. So we make sure the installer understands that at the edge angle, the depth of the growing media must be exactly compacted in the cup wells to 3 inches plus. A shallower depth may not be significant at the center, but at the edge you must have that specificity in quality control to safeguard against erosion.
Finally, once the plants are down, we place a “jute net” over the entire assembly. Our erosion blanket is a biodegradable coco-fiber. It is really important on the perimeter that the jute net is wrapped around the vegetation and under the soil profile at full depth to make sure the plants have the best chance.
What were some other ways you adapted the green roof for this project?
One unusual thing is we infilled the drainage element with an aggregate. That’s not totally uncommon on a green roof assembly, but it is on sedum. We wouldn’t do that at a lesser height, but it served as ballasting. The mineral-based aggregates we use also wick the water saved in the cups up into the growing layer, which in this case had a slightly higher dry weight (28.9 pounds per square foot) than a traditional assembly, again primarily for ballasting.
Dry weight always compromises nutritional content in the media. That means you can’t think strictly about weight, or you lose plant vitality. This was a balancing act we performed with CANY — to make sure proper weight was maintained for ballasting without undermining the needs for plant life, while also keeping the fully saturated weight within the load-bearing requirements of the structure.
What about the installation?
Green roof design, engineering and global experience are important, but the success of a green roof also depends on the installation. We worked with Nations Roof on proper installation technique, both generally and specifically for this challenging installation, and they did a fantastic job.
Building Management: SL Green Realty Corp., New York, www.slgreen.com
Construction Management: CANY Architecture and Engineering DPC, New York, www.cany.com
Roof Waterproofing System: Kemperol 2K-PUR cold liquid-applied reinforced membrane system, Kemper System, West Seneca, N.Y., www.kemper-system.com
Green Roof: Custom Sedum System by ZinCo USA, Stoughton, Massachusetts, www.zinco-usa.com