"Creating a living green roof" Briornis-Aesthetope Avian Habitat Green Roof
Lower Manhattan, NY, USA
Biornis-aesthetope: Living Green Roof System
The green roof system of the proposed Biornis-aesthetope provides benefits which far surpass those of typical extensive and intensive green roof systems. During the design process, the strategic management of a matrix of variables, ranging from the use of organic and inorganic soil substrates, gradients of water retention, insect hibernation patterns, and vegetative planting; to the resulting structural loading and construction cost, allows the Biornis-aesthetope green roof system to be flexible through its myriad iterations and still function as healthy biotope.
The typical benefits of a green roof are economic and environmental. The benefits of Biornis-aesthetope are sociopolitical at a global scale, and are cultural at the local scale. This green roof’s ability to produce a living habitat—a community of flora and fauna, waxing and waning, growing and dying, changing through the seasons, and maturing through the decades—provides a constant, sustainable, and renewable interest in the performance of the green roof.
Biornis-aesthetope provides a green roof able to produce the correct conditions for the creation of a biotope. The sculptural expressiveness of the green roof is necessary for the completion a sustainable biotope. Equally important to environmental considerations, Biornis-aesthetope creates an icon for New York City in the very location that America’s heart and national psyche feels a void has and yearning for expression, identity, and icon.
The Biornis Aesthetope green roof will not only be an international sociopolitical icon, but also its performance as a green roof will be an icon and milestone for the “green” movement as well as the green roof industry. Among the traditional benefits of a green roof are the reduction of heat island effect, reduction of carbon dioxide effect, the reduction or airborne particulate matter, reduction of rainfall run off impacts, reduction of heating and cooling loads, and the lengthening of roof life.
However beneficial typical green roofs can be, in the majority of cases, they cannot support habitats. The reason for this is that they are almost entirely made from artificial materials. In considering the entire construction assembly, everything except the plants themselves are created from artificial materials. To keep the weight of the assembly as light as possible, the soils usually contain as little as 5% organic material. This means that 95% of the materials are inorganic and manufactured. Artificial materials not necessarily bad, as they allow the weight of the roofs to be such that they are affordable and applicable in many situations; however, they are not sufficient for the production of a sustainable ecology.
The green roof of Biornis-aesthetope utilizes both organic and inorganic soil mixture types. One type is used in the extensive roof system, with inorganic soil mix, and the other type is an intensive green roof system, with a deeper technical section, ranging from 12 to 36 inches and containing soil mixtures with no less than 15% organic matter. 15% organic matter is crucial for insect habitation because without organic matter insects cannot be sustained. If the insects cannot be sustained, then the birds will not have a food source, and without a food source, birds will not use the roof as a refueling station, and if the birds do not use the roof, then the energy of the roof as a living organism cannot exist.
The depth of the intensive organic soil regions is important because it allows for vegetative plants to grow, which yields alternate and differentiated food sources. This is necessary for the creation of a community with complex ecological relationships. In the intensive regions of the green roof, the combination of soil depth and organic matter allows those regions to create biological identity and take on unforeseen characteristics as well a additional plant species that were not part of the original plantings. Eventually, tree saplings will take root. To prevent the growth of large trees (which the structure will not be able to support) the roof must be maintained twice a year to free it of saplings beginning to take root in the intensive regions.
The following memorandum prepared by Buro Happold Consulting Engineers PC, covers various potential project drivers and green roof design consideration in addition to the expected benefits from these proposed design strategies.
Project Drivers
LEED for New Construction (NC) The project is likely to be pursuing LEED NC Certification. Green roofs can assist a project in meeting qualifications for multiple LEED NC points. Green roofs relate to the following LEED NC points:
SS Credit 5.1 - Protect or Restore Habitat SS Credit 6.1 - Stormwater Design Quantity Control SS Credit 6.2 – Stormwater Design Quality Control SS Credit 7.2 - Heat Island Effect: Roof WE Credit 1.1 – Water Efficient Landscaping: Reduce by 50% WE Credit 1.2 - Water Efficient Landscaping: No potable Water Use or No Irrigation ID Credits - Innovation in Design
In total there are 7 - 9 LEED credits which the Green Roof may assist in achieving. Innovation in Design credits may be received for the creation of habitat above and beyond typical efforts and for creative means of addressing all of the other relevant points by utilizing the adjacent property. Although the hotel roof is not a conventional interpretation of the project site this area could be included within the site area calculations and the LEED review.
PLANYC 2030 Recently NYC Mayor Bloomberg announced plans for a sustainable NYC by the year 2030. This plan is called “PLANYC 2030”. Strategies for achieving the goals and objectives have been made public. (http://www.nyc.gov/html/planyc2030/html/plan/plan.shtml). Relevant Goal: GREENYC Relevant Objectives: 7 reduce global warming emissions by more than 30%. 8 achieve the cleanest air of any big city in the United States. 10 open 90% of waterways for recreation by reducing water pollution and preserving natural areas. Relevant Strategy Proposed: Water Quality #8: Provide incentives for the installation of green roofs. The green roof would certainly help the city in achieving many of its Sustainability objectives. It could be assumed that any project that embraces PLANYC 2030 will have a leg up on other design proposals and will receive project support from government entities.
Design Drivers Soils and Plant Selection The roof of the hotel will not be able to support a green roof (maximum 20+ psf load bearing capacity). However, the columns of the hotel may be able to support a green roof. Thornton-Tomasetti will consult BAM on this load bearing capacity. It is likely that while the hotel may be able to support an extensive green roof with combined soil and drainage mix depths up to 8” inches an intensive green roof (greater than 8” soil depth) will not likely be feasible. Given the extreme environmental conditions associated with an extensive green roof (shallow soil depths, high winds, high temperatures and intense solar exposure result in highly variable soil moisture levels) to support all but a few native plants. The core of the plants would have to be non-native Sedum. However, a few native succulents (Talinum) and plants like native allium may be mixed in. There are a handful of plants that may establish, but their survival cannot be guaranteed (e.g., Tradescantia, Muscari, Crocus, Antennaria, Solidago). Please note that all of the native herbaceous plants mentioned are either seasonal or deciduous. The native Sedums (there are a few) cannot be established from cuttings and grow very slowly.
Stormwater Runoff A 2-6” green roof covering 90% of the hotel roof surface (62,500 sf) would result in a 60% reduction in stormwater runoff or -1.1 million gallons per year. The 700,000 gallons of “excess” stormwater could then be harvested for irrigation of the green roof, resulting in zero net stormwater runoff from the roof area. Benefits of the green roof and stormwater runoff reductions will be felt on a greater, citywide scale due to reduced stormwater loads to the cities CSO infrastructure, resulting in water quality improvements (see PLANYC 2030). Drainage and Irrigation The green roof drainage system will allow for saturation of soils and then removal of excess water collected at the impervious layer/drainage medium interface. Excess water will drain to a number of collection tanks in order to spread out water storage weight. Stored water will be used for irrigation of the green roof during dry periods. Rainwater Harvesting tanks (upon approval from the structural engineer, Thornton-Tomasetti) should be located upon columnar structural support locations. A pump will be necessary to distribute water to any planted areas with a higher elevation than the tank base. A 10,000 gallon storage tank (1,350 ft3) would store enough water to irrigate roughly 1/3 of the green roof to a point of saturation. Our drawings show that roughly 25% of the green roof is intended to have irrigation. Rainwater harvesting would reduce potable water consumption by 100% or save roughly 500,000 gallons per year.
Suggested Urban Migratory Bird Species The following is a short list of Migratory Birds of the Atlantic Flyway that have been reported as present and accepting of urban environmental conditions. 1) Black-throated blue warbler 2) Common yellowthroat 3) Magnolia warbler 4) Ovenbird 5) Swainson’s thrush 6) Veery 7) Wood thrush 8) Yellow-rumped warbler 9) Peregrine Falcon
