The Pavilion [Living Roof Installation] — Aspen Vermont

The Pavilion [Living Roof Installation] - Aspen Vermont

The Pavilion: [Living Roof Installation]

May 2013

Kelly Ferguson and Linda LaCroix describe details of the installation of a living roof on a waterfront pavilion.  

Aspen recently completed an installation of a green roof on a waterfront pavilion. The benefits of green roofs are not necessarily widely known. In this article, we introduce the reader to vegetated building systems and explain important benefits that they offer to the built environment.

Sedum layer.

What Is A Green Roof and How Does It Work?

Green roofs are living building systems located on building roofs in both urban and rural settings.  The location of the building determines how the green roof with be used and how extensive the system will be.  Green roofs consist of plants built up on drainage trays that are then laid onto existing roof membranes.  The entire green roof system includes: high quality water proofing, drainage system, filter cloth, and a growing medium for plants.  As time lapses, the trays grow together to form a single green surface.  Green roofs operate by providing a plant layer, typically sedum, that remains moist to facilitate vegetative growth and minimize maintenance: sedum layers can withstand drought conditions up to about two weeks before requiring water. This layer provides a thermal layer and passive cooling system for a structure.

There are both intensive and extensive green roof systems.  Intensive green roofs are able to sustain not only agriculture, but also walkways and seating areas elevated above a structure or open space. Intensive systems are utilized in outdoor urban park systems.

They contain a foot or more of growing medium and can hold up to 150 pounds per square foot. Given the layer complexity of intensive roof systems, they require extensive maintenance.  See Chicago City Hall  and Dartmouth College Life Sciences Building  for examples of intensive green roofs.

Syracuse Center of Excellence

Extensive green roofs consist of native vegetation, are not intended for human occupancy, and weigh roughly 20 pounds per square foot.  Extensive green roofs generally require little maintenance.  See the Syracuse Center of Excellence for an example of an extensive green roof.

How To Install A Green Roof

Making the connections between the modules.

Installing green roofs are simple.  After a few months of vegetation growth, the sedum is delivered to the site as a fully developed landscape system.  The system is put in place in five easy steps as follows:

  1. Prep the pitched roof with a rubber roofing membrane such as EPDM (ethylene propylene diene monomer).
  2. The polypropylene trays are then placed adjacent to one another on the prepped roof.
  3. Trays are then connected with overlapping lips to stabilize the trays in place.
  4. Remove soil elevators that are in between the trays to allow the plants to grow together over time.
  5. Water the green roof after all trays are installed to allow for the soil to settle.

Gathering soil elevators that were removed from the sedum.

Green roofs can be installed on existing roof systems and are not limited to new building construction.  Green roofs are an extensive expansion onto an existing system and require the roof slope, loading capacity, accessibility, drainage, waterproofing, electrical and water systems currently in place, and wind and sun exposure.

Benefits

As mentioned, green roofs can be used in both urban and rural areas and the benefits differ depending on the location.  Green roofs are generally a more expensive roofing system compared to traditional approaches, however, green roofs provide superior protection from the harsh environment: for example, a green roof can add 30 years to the life span of a 20 year roofing membrane. As a result, the

NYCGR crew with sedum modules.

upfront cost is well worth the investment.  Green roofs also save on energy consumption.  The system provides a thermal insulation layer that mitigates heat gain and loss, thereby reducing energy consumption due to normal heat fluctuations.  Green roofs use heat energy known as evapotranspiration. “a term describing the transport of water into the atmosphere from surfaces, including soil (soil evaporation), and from vegetation (transpiration).”[i] This naturally occurring, passive process cools the air surrounding the green roof in warmer months.

Green roofs in urban environments help to mitigate water runoff that would normally flow into storm water drainage and treatment.  The roof absorbs water it needs to grow thereby preventing gallons of water from running into sewer systems.  Green roofs also address a critical problem in urban settings called the “Heat Island Effect”, describing the increase in temperatures in urban and suburban environments due to the copious amounts of impermeable and reflective surfaces that as a result, tend

to use more energy cool their buildings. “Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.”[ii] In contrast, green roofs are not reflective and thus mitigate rising temperatures and related consequences.

Green roofs not only provide innovative and simple technology to a long standing problem, they also provide a lush, cool retreat for building occupants.  Green roofs that are not accessible still create scenic views, passive heating and cooling and attract wildlife. In certain parts of the world, green roofs are created to protect endangered species by mimicking their natural environment in a controlled and contained setting.

NYC roof garden.

Green roofs provide a supreme setting for vegetation that provides additional benefits: restaurants can bring flora, herbs and vegetables grown on green roofs to the table.  This urban food supply helps reduce the amount of time from “farm” to table, helping to facilitate the evolution of urban and vertical farming.

Green roofs complement other technologies to help increase green energy efforts.  As the temperature increases on roofs with solar panel installations, the efficiency of the solar panels decreases.  Green roofs increase solar panel efficiency by reducing the ambient roof temperature.  This effect is increased with the installation of vegetated planes on a structure’s vertical surfaces.

Future Applications & Changing Technology

Certain cities have created mandates that require buildings to install green roofs.  There are also several conferences that are now dedicated to green roof technology.  The future of green roofs lies in the plants.  Currently a majority of green roof systems use a sedum substrate,

Urban vertical garden.

which is a low growing genus that captures water in its tiny leaves.  Recent research suggests that in the future green roofs will move more and more toward tall grasses and shrubbery because the biomass of a larger plant is able to hold more water than a smaller plant.

Increased use of vegetated building systems depends on how well architects, builders and installers educate property owners on long-term benefits.  In Western European countries, green roofs are commonplace; the United States has yet to catch up advocating for green roofs with the same vigor.  As Americans continue to learn about the importance and equity inherent in passive technologies as a means to creating better built environments, the benefits of green roofs will become more apparent.

For more information on how a green roof or wall application can benefit your project, email us at mail@aspenvermont.com .

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