Green Roofs

Why have an ordinary roof of no value, when instead you can build a living roof and benefit the environment and your city? People in cities around the world are choosing to turn the negative space of a traditional roof into a garden on both residential and commercial buildings. There are millions of acres of rooftops around the globe that could be converted to green space.

A typical green roof consists of many layers. Vegetation lives in a growth medium; an engineered soil composite is used to reduce the weight. Several membrane layers lie underneath the soil. A drainage layer allows excess water to flow freely and a root barrier layer prevents the roots from penetrating the roof. There are two types of green roofs: intensive and extensive. Intensive green roofs require a fair amount of regular maintenance but can sustain a wide range of plant species. Extensive roofs are more common because they require less work. Extensive roof soil is typically only 2 to 4 inches deep compared to 1 or 2 feet of soil in an intensive roof. A shallower depth inhibits weeds from establishing themselves on the roof.

There are many benefits to these living roofs. They help to reduce storm water run off by absorbing rainwater. The water that does drain off flows slower and is cleaner because the vegetation and soil mixture act as a filter. Green roofs can help reduce the amount of storm water that has to be treated by municipal water treatment plants and therefore lessens the threat of sewer overflows.

Although the installation cost of a green roof is typically two to three times more than a traditional roof, energy savings can make up for this initial expense. The vegetation and soil of green roofs act as effective insulation, reducing heating and cooling costs by as much as 20 percent.  This additional insulation also acts as a sound barrier, which is pleasing for homeowners close to busy highways or noisy streets. The reduction of the urban heat-island effect is a large advantage provided by green roofs since they stay cooler than conventional roofs.

The sun breaks down the material of traditional roofs over time and forces homeowners to replace the roof. The shelter that the vegetation and soil provides can greatly increase the roof life span. Green roofs can also create a habitat for wildlife. Birds and insects can easily find homes in the living environment of a green roof. It is even possible to graze goats!

In Portland, Oregon, fee reductions and other incentives encourage builders and homeowners to consider green roofs. In Germany, approximately 14 percent of the country’s total roofs are green partly because some cities levy a tax on conventional asphalt rooftops. Living roofs are required by law on roofs of suitable pitch in some cities in Germany, Switzerland, and Austria. Although the number of green roofs is increasing in America, extra incentives could help to speed up the trend.

So why not swap your shingles for vegetation? Utilize the wasted space to help reduce storm-water runoff, increase energy efficiency, and enhance your neighborhood surroundings.

Sources:

Klinkenborg, Verlyn. “Up on the Roof.” National Geographic May 2009: 84-103.

Colwell, Dara. “Green Roofs: Building for the Future.” Alternet (2007): 31 Jan 2010.

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6 Comments

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6 responses to “Green Roofs

  1. cseberle

    Another option to help out with indoor temperature control that has caught on quickly out west is using an earth berm around the foundation of a structure. It’s a fairly simple idea where builders push earth up around the sides of a structure (usually about half way up the outside walls) which creates insulation and reduces the amount of energy used to control the temperature inside.

    The first time I noticed this technique was when I was touring wineries in the Willamette Valley over break this winter. While I haven’t seen this catch on with residential construction I was amazed how many of the wineries in Oregon and Washington used this technique on their warehouse and holding areas. A few glasses of wine deep at Carlton Wine Studio in Carlton, Oregon I began talking to one of the co-owners who estimated that the earth berm saves them an average of 15% on their heating and cooling energy usage. And they’re not alone, dotted all up and down the valley I began to notice winery after winery that used this technique and I’m sure financially benefited from the reduction of energy usage.

    http://www.hamacherwines.com/hamacher/page/winery.jsp

  2. Alan DeLaRosa

    Both of those ideas, a green roof and an earth berm appear to be great ways to save money and reduce energy use. However, I feel like this blog is one-sided and only mentions the positive aspects to green roofs. Now, please don’t get me wrong and think that I am against energy-efficient homes, but a few questions came to mind as I read this blog.

    A green roof appears to be cost effective over time, but as you said, “the installation cost of a green roof is typically two to three times more than a traditional roof.” Is that for a house that is designed to have this type of roof? What about for a house that already has a traditional roof?
    Also, I am curious as to what “an engineered soil composite” is made from, how it is made, and what the energy consumption is to make it.

    Another issue is about the upkeep for this type of garden-roof. A lot of people barely have time to take care of a traditional garden on the ground or they live in apartments to avoid the responsibility of a garden. So even though the initial monetary investment is paid off by energy savings, there seems to be a time commitment as well that would always be there.

    One final thought that came to my mind is about the type of vegetation that could survive while being exposed to direct sunlight all hours of the day. I know from experience that plants can be dried out from the Texas sun if left out all day. Most small plants need some kind of shade for part of the day like from the shadow of a house or being at the bottom or a forest with taller trees blocking the sun. I think adding another structure to shade the plants on top of the green roof would be defeating the purpose of the green roof. Also I don’t think it would be possible to have a small forest of trees in 2 to 4 inches of soil.

    With all of that being said, I hope that there are solutions to my concerns and that in the near future initial investment costs will decrease so that it appeals to more people. I think that if I ever had the option to, I would choose to have a garden on my roof; to me the advantages outweigh the disadvantages. I enjoyed reading your blog, thanks for the information.

  3. reasmacken

    I have seen this method employed in Detroit, MI and it made me wonder why I had not heard more about this option or seen more employed in other cities I have visited. Considering the expense, I was surprised that a city going through such tough economic times, much worse than many cities that have been affected by the economic downturn, had decided to make use of this “green” technology in some of its newer buildings.

    I am sure that it will be much tougher to employ a technology like this in Austin, or most of Texas for the matter, considering the heat and potential for extended periods without rain. In any case, I will be interested to see if this technology begins to catch on in other cities where it is feasible.

  4. dhjohnston

    Green roofs are one thing, but when I was in Southern France last year, I came across something I hadn’t seen before: A garden on the facade of a massive building, the Les Halles Department Store in Avignon.

    The facade of the whole building is covered in vegetation — it was done by the pioneer “Vertical Gardener”, Patrick Blanc. Academic literature does not seem to have been published yet, since Blanc essentially developed the method for soil-less plant growth along sheer walls only in the past few years.

    However, I speculate that if green roofs can capture up to 20% energy savings, then enclosing your building envelope with vegetative insulation that utilizes all natures elements for its own benefit, seems to balance the entropy bill, and also offer potential for even greater energy savings. All the sites I’ve read on Vertical Gardening state that it can be done anywhere; any climatic condition, any geographic location, and any solar orientation.

    While I was in Avignon, the vegetation on facades of buildings had an even greater impact on the general public than seeing some of the cathedrals in all their gothic splendor. The green facade really connected with folks pleasure sensors — the Les Halles constantly had people milling about it’s plaza. In my case, as I stood in awe looking at a whole department store covered in over a dozen different types of foliage, I watched many others stop for the same reason — to simply soak in the beauty of vegetation along a wall.

    Apparently the design of such a system is not too difficult…
    According to a guy who has a DIY Vertical Garden website, the directions are such:

    “The three-part system consists of a PVC layer, felt, and metal frame, providing a soil-free self-supporting system light enough to be hung on the wall, and even suspended in the air, weighing in at less than 30 kilograms per square meter.”

    I suspect that a place like Austin, TX has potential for vertical gardens — an innovative urban gardening community that has a strong grass-roots presence in the neighborhood councils, the residents generally have environmental leanings, and the natural benefits of the Vertical Garden include the improving indoor and outdoor air quality surrounding the building envelope.

    It would delight me to see more of this meld of technology, creativity and engaging civic interest in our own town. Feel free to learn more about the practice — If you want to begin your own vertical garden, Flora Grubb Gardens has a great DIY blog. http://floragrubb.com/florasblog/?cat=3

  5. mmetteauer

    You raise interesting idea on green roofs and other initiatives that can help reduce residential energy consumption. The other issue to consider is historic preservation and the design and aesthetic for residential neighborhoods. Richard Moe, president of the National Trust for Historic Preservation, spoke at a 2008 conference in Berkley, California, where he estimated that it takes decades for new, “green” buildings to re-coup the energy wasted in demolishing existing structures, which may lack energy-saving features. The costs of retrofitting homes with this type of amenity can be great – not only in the actual material and installation fees, but also the cost of destroying existing roof structure and disposing of it.
    Some green technologies easily lend themselves to retrofitting older homes or even historic neighborhoods with things like solar panels. It’s a different story when you suggest ripping traditional roof (say in the case of historic Austin, a gabled or hipped roof) to install a flat, “garden-based” roof that, alhtough it may have some benefits, will forever alter the exterior streetscape of a home and its surrounding properties and remove historic significance. Perhaps in new construction, this type of green building would be more appropriate. In advocating policies to embrace green building, the U.S. Green Building Council’s LEED program should develop better guidelines to address the repair and preservation of existing housing stock, particular those areas that were designed to promote density and are located in urban core areas.

  6. rs32463

    Green Roofs can be both beautiful and resourceful if constructed right. The question is what is right. There is a group called GROWERS (Green Roofs: Working Expertise + Regional Solutions) that is trying to set the criteria for the construction of regional appropriate green roofs here in Austin. They have held panel discussion at City Hall, have meetings with green roof specialists, and visit green roofs sites throughout Austin. You can always find more information about the group at http://www.growersaustin.com

    About a year ago I attended a site visit with the growers group to tour the largest green roof in Texas, which happened to be here in Austin! It is located on top of the Palisades West Office Complex parking garage. The Palisades is on the corner of 360 and FM 2222. When driving on 360 as you are approaching FM 2222 if you look west you will notice large trees growing on top of a roof!

    At the site we met with developer Tim Hendricks of Cousins Properties who gave us a tour of the roof. This impressively large green roof is more of a roof top garden with various plants and trees. It also has stone walkways and many benches where one may enjoy a nice lunch break. The green roof is not open to the public and is only for use of the Palisades Office Complex. Its soil depth is approximately 2 ft deep with specially constructed pockets for the trees with a soil depth of 4 ft. The construction of this green roof doubled the cost of the parking garage.

    Though the green roof is beautiful it is not resourceful. A green roof is used to cool a building and help with water run off. This green roof is atop an open parking garage where a green roof’s cooling benefits are not beneficial. This green roof is more ego friendly than eco friendly. The construction of this green roof shows how important it is for more active discussion regarding incentives and green roof knowledge here in Austin so that we may build resourceful green roofs.

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