Walls & Roofs Magazine takes a look at pioneering, decade-old green roof projects and some of the latest, state-of-the-art roofing constructions.
The concept of green roofs isn’t new, but architects and design professionals have only been giving these roofing systems more attention over the past two decades. As the concept of sustainability continues to grow and clients become more and more educated on the various benefits that green roofs have to offer, architects continue to raise the bar on what can be done.
The traditional idea of a “green roof” conjures images of an aerial view of a sparsely planted rooftop garden. Today sophisticated green roofs include everything from manicured landscapes and mazes to pathways, fountains and ponds that create dramatic results and lead to lasting sustainability impacts.
Green benefits of green roofs
• Rainwater absorption.
• Insulation advantages.
• Creating a habitat for wildlife.
• Decreasing urban air temperatures.
• Mitigating the “heat island effect”.
• Psychological benefits to an aesthetically pleasing environment.
Ford’s ten-year-old green roof
Today there are over 10 000 green roofs in the United States. Back in 2003, when there were only 50, Ford Motor Company became the host of the largest green roof in the world.
Now more than a decade old, the green roof (which is located on top of Ford’s Michigan River Rouge truck factor) remains the largest living roof in North America at 10,4 acres (4,2 hectares) and it entered the Guinness Book of Records in 2004. The roof was constructed to last twice as long as a conventional roof, but it is already outperforming this original estimation.
Preeminent green architects, William McDonough + Partners, designed the roof so that it is composed of drought-resistant species of sedum. The sedum attracts beneficial butterflies, insects and birds.
“It sustains a dynamic ecosystem of over 35 insect, spider and bird species, and eleven plant species. Within five days of the living roof being installed, local killdeer had nested and laid eggs in the sedum,” said the founding principal of William McDonough + Partners, Bill McDonough.
One of the most remarkable things about this pioneering project is the fact that it wasn’t necessarily about “going green” – Ford’s green roof was an economic necessity. Thanks largely to runoff from the factory and parking lots, the neighbouring Rouge River was polluted.
The company estimated that it would cost approximately USD$50 million to clean up the toxic stormwater, so they partnered with green architects to design a roofing system that mimics nature instead of investing in a chemical-based stormwater treatment plan. The landscape-based infrastructure, which requires the minimum use of pipes, cost USD$15 million to create – less than a third of a conventional stormwater system practices, and it also paved the green roof industry so that even more spectacular, inspiring and economically viable projects can be achieved today.
The biggest hospital in North America, Centre Hospitalier de l’Université de Montréal (CHUM) is set to feature a green roof that grows medicinal herbs. The USD$2-billion, 772-bed project is set to be completed in 2018. The roof gardens with all sorts of aromatic herbs and plants were designed by the innovative Montreal-based firm NIPpaysage.
The hospital is planning on investing in seven different plant beds that will house twice-tested medicinal greens. The herbs selected will all have demonstrated measureable capacities to aid in healing various ailments.
Besides housing medicinal herbs, the architectural drawings show that the herbs will be planted in designs that show the actual form of the plants as they grow in nature. The architects, Canon Design, designed the building with a gleaming glass wall on the exterior that will translate to a peaceful and light-filled space for patients.
Starbucks green roof
Project name: Starbucks Green Roof, Downtown Disney, Walt Disney World.
Location: Orlando, FL, USA.
Building type: commercial.
System: single source provider.
Size: 1 800 square feet.
Access: inaccessible, private.
Located just past one of the main entrances of Walt Disney World in Orlando, the new Starbucks highlights the green roof of its 500th LEED store. Not only does it offer the many benefits that green roofs offer to its surrounding environments, but it also gives Disney visitors an opportunity to view an imaginative and sustainable green roofing design.
Some of the benefits to the environment include being able to attenuate and clean stormwater, remove particulate matter and cleaning rainfall before reaching the building’s water systems. Senior designer for Starbucks, David Daniels, created a green roof that consists of hundreds of lemongrass plants. Florida, having a hot and tropical climate, makes lemongrass a wise choice for a green roof.
“We had all the grass grown in a nursery and we fed it with compost from our coffee grounds from a nearby Starbucks store. This gesture is one of the many ways in which we’re able to tell our story,” says Daniels, before explaining his thought process behind creating the green roof of the Disney Store.
The roof is designed to be hurricane as well as tropical storm resilient. The complete assembly growing system is permanently attached to the underlying building and it boasts cradle-to-cradle sustainability, seeing as coffee grounds from the Starbucks store are composted and used to feed the plants and the plants, in turn, clean the water and air (thereby helping coffee beans to grow).
The sustainable eco-system is accentuated at night with LED lighting. Kevin Songer from MetroVerde Green Roofs Roofing Contractor, the contractor on the job, said that sometimes the hardest part of a green roofing project is the unforeseen issues.
“This is why it is always so good to hire a veteran team of the trade, staff who understand what plants or soil media to use and the proper growing system to install,” wrote Songer on his blog.
“But just as important to a successful green roof installation as the plants or soil or the system is the overall concept of staging and logistics. If you cannot get soil media or plants up on the roof, then you are not going to have a green roof. This knowledge usually comes through the school of been there, done that,” says Songer.
Considering access issues related to green roofing projects is not usually something that is discussed during the design stage of the project (leading designers to assume that it won’t be a problem).
“Even on a small green roof the task of moving three or four cubic yards of soil media up ten feet in the air is a daunting task. When access to the side of the green roof building is clear and free of construction materials or tools, then the lifting up of soil media super sacks or heavy ballast is much easier accomplished. Carrying five gallon buckets of soil media up a ladder is a tough way to apply growing media to a roof if there is no access for a lift truck,” says Songer.
Songer said that he once received advice from one of their roofing partners that he applies to all projects: Always write in a contract something to the extent that appropriate access to the roof area must be provided by the general contractor.
“This is really good advice. Staging soil media and green roof plants requires a significant amount of space. Most construction sites are filled with either waste bins, stacks of materials or large pieces of very heavy equipment,” says Songer.
Besides access, logistics need to be considered throughout the project. Everything from where the plants will be stored to where the planned staging areas will be before the roof is installed, need to be considered.
Are green roofs better in uninsulated buildings?
While green roofs have been recognised as a great means of limiting the urban heat island effect, the application of green roofs is often limited due to the additional construction costs and the inability of design professionals to accurately demonstrate what the potential energy savings and comfort benefits are that will be achieved during the design stage of the project.
Researchers from the University of Nottingham, however, changed this thanks to a study that allowed building practitioners to calculate the potential reduction of heating and cooling loss that a green roof can offer.
In a paper by Georgios Kokogiannakis, Annegret Tietje and Jo Darkwa at the Centre for Sustainable Energy Technologies at the University of Nottingham, entitled “The role of green roofs on reducing heating and cooling loads: A database across Chinese climates”, detailed modelling techniques were used to develop a database for assessing in a quick and easy way the energy performance of green roof designs across a range of Chinese climates.
The research team focused on heating and cooling loads by calculating indoor temperatures, using the EnergyPlus simulation tool. The study covers 5 328 configurations by varying model parameters such as location, climate, seasonal periods, glazing type, wall insulation levels, roof insulation, soil thickness and condition, and vegetation density characteristics.
The results of the study showed that green roofs can offer significant energy savings for heating and cooling loads if they are applied on roofs without insulation, but only limited energy savings where heavy insulation on the roof is also applied.
Different green roof configurations will have different effects on the heating and cooling loads of a roof. All of the 5 328 cases were studied with and without the green roof. Large amounts of data were extracted from the simulations and put into a database in order to draw results and conclusions. The results showed that green roofs could significantly reduce heating and cooling loads for buildings that are not heavily insulated. The energy benefits from the green roof application, however, are slightly less during the heating season when compared with those for the cooling season.
“For heavily insulated buildings green roofs can offer small benefits in terms of heating and cooling load reductions. It should be noted here that such heavily insulated buildings, as those for cases 133 and 139, are not common practice in China,” states the study.
Heavily insulated buildings have also not been common practice in South Africa. However with the introduction of the Energy Efficiency Regulations in South Africa in 2011, the installation of thermal insulation is now compulsory in certain building occupancy classes.
“China has a climate dominated by dry seasons and wet monsoons, which leads to clear temperature differences, bitterly cold winters and unbearable heat in summer months. We do agree that the green roof top or cool roof concept can significantly reduce a building’s cooling load and increase comfort levels by reducing the temperature inside a building during summer months however one would still need to consider some form of insulation as it can also create a very cold building interior which would increase heating costs in winter months” says Des Schnetler, chairlady of the Thermal Insulation Association of Southern Africa (TIASA).
For more information, visit www.nottingham.edu.cn, www.tiasa.org.za, www.starbucks.com, www.ford.com and www.kevingsonger.blogspot.com, to which full thanks and acknowledgement are given.