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Kimberly Powell

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If green roofs were mandatory in cities would there be less development and building?

William McDonough knows the benefits that come from designing and implementing green roofs. McDonough has helped design living roofs for big companies such as Nike and Ford Motors. But many companies and homeowners overlook the benefits of green roofs. One benefit of green roofs is that they keep the internal temperature of a building steady throughout the year. The National Research Council of Canada found that having a green roof reduced the daily energy demand for air conditioning in the summer by 75%. Toronto is the first North American city to pass a law mandating green rooftops for all new residential, commercial and industrial developments. Any new construction with floor space of more than 2,000 square meters must devote between 20 and 60 percent of its roof to vegetation. But with green roofs comes an unwanted financial upfront cost. Will developers decide that the benefits outweigh the costs for installing green roofs?

If green roofs were mandatory in cities would there be less development and building?

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  • May 27 2012: I'm wondering how these plants on green roofs get watered. Here in Oregon this probably is answered by rainfall, but what about in a place like Arizona? Do they have to pump water up to the top of the building to water the plants? If this is what happens I would be skeptical that green roofs are actually helping the problem in this case, especially on very tall buildings. Maybe I'm completely wrong and green roofs benefits would still outweigh the water cost even on really tall buildings in Arizona, but I have to think that perhaps placing solar panels on top of those buildings may be a better use of the space. I believe solar panels can accomplish the same absorption of light and reduce the cooling costs, and in areas with lots of sun and little rain their energy production may outweigh the other benefits of green roofs.

    I think in certain areas green roofs are a brilliant idea, in Portland for example I would love to see this law implemented. I don't think that requiring green roofs all over the country is a good idea. I think the government should offer incentives to cities to enact this law on their own, but leave it up to the city (or maybe the state) to decide whether they require green roofs. These more local governments should look into what would help their area the most.
    • May 27 2012: It's standard procedure with green roofs to mandate that the plants are native species that will survive in the naturally occurring climate. In the south west this means that green roofs are a lot of desert plants that might not get as luscious as our Northwest plants but they serve the same purpose, and contribute to the concepts of bioregionalism and the cultural values of nature spaces.
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        May 28 2012: Up and coming architects may have a hard time selling the idea of sage brush on building roofs. When most people think of green roofs, they think of them as green. It doesn't matter whether they live in the Northwest or the desert, we have come to expect it.

        I agree with Mat that the movement of water up a building is a terrible waste of energy and water, which is scarce in the desert as is, and Ellen is right that the flora should be native. A national law mandating green roofs, however, will just mean more "inequality." The Northwest will build the desired "green" roofs while Arizona grow their cacti. I wouldn't have it any other way, but this federal law would meet endless resistance if any part of it mentions native plants. We like to design landscapes that oppose nature rather than work with it and many parts of America would oppose their native plants as fixtures for their green roofs because they don't find them aesthetically pleasing. I think a policy such as this would only work at the municipal level.
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          May 28 2012: I disagree. I think you would have to do at the very least a statewide law. Nationwide would be better. I don't think "green" roofs should be the only option (small windmills or solar panels would be perfectly acceptable substitutes) but if you don't implement the law everywhere, companies will just go to a state or county that doesn't have the law to build large structures, and the states or counties with the law will cry foul because they're loosing tax revenue and jobs. Companies change locations for a few percentage difference in taxes, and I have no doubt that they'd move development to get out of paying for a green roof if it added significant amounts of money to building costs.
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      May 27 2012: I agree that in certain places there should be incentives or requirements to have green roofs on new buildings. In the pacific northwest many people are very conscious of the environment and I think most would love the idea. If it can reduce our excessive need for air conditioning and maybe even keep the buildings warmer in the winter, I agree that it should depend on the area and the plants would need to be natives so that they are adapted to the area like Ellen said. I don't agree that solar panels could accomplish the "same absorption of light and reduce the cooling costs" because it takes a lot of energy to make those solar panels and the green roofs need little to no maintenance. Yes sometimes especially when they are being established may need water, but if they are natives they should be fine with the weather of the area. If water is the problem, most tall buildings already have water running to the top floor so what would be the difference between one more floor?
      • May 28 2012: I know that constructing solar panels is not exactly a green process. What I meant is that once they are up the solar panels will do the same job as the plants in absorbing some of the incoming light, which will lower the amount of cooling the building needs.

        Also little to no maintenance? Not to harp on this solar thing, but they require little to no maintenance. I just don't see how plants baking in the sun all day could possibly not require maintenance. Again, I'm speaking with regards to certain areas. In the PNW I'm sure the plants would require little to no maintenance and would be a better solution. I don't mean to say I think we should change the idea to solar roofs instead of green roofs, I just think solar may be a better way to go in certain areas.
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          Jun 1 2012: Okay, maybe in some areas it would be reasonable to use solar panels instead of a green roof, but if in areas such as Arizona, using plants native to the area would allow them to survive as long as they were established. Solar panels would just increase the use of Air Conditioning because people would think that it is not harming anything, when it is just decreasing their reliance on the power grid to power their air conditioner.
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      May 28 2012: While Ellen's point solves the problem about water I he to wonder what about nutrients? Even if something is grown in its native habitat that doesn't mean the provided soil will be able to support it and many plants deplete nutrients that are in the soil with every growth cycle. I'm not an expert on farming but depending on the plant types that grow in that area a lot of external fertilizer would have to brought up, especially nitrogen, yes? Ironically this would be an especially be problem in tropical areas because most tropical plants can only thrive because of the massive amounts of dead plant and animal matter that can be found in the topsoil of rainforest like environments. Of course providing external fertilizer is already business as usual for farms but I'd think that needing to distribute fertilizer to the top of every building would complicate matters considerably, and I could be wrong but I think potted plants (which is essentially what green roofs are, only on a larger scale) usually require more externally fertilizer than plants that are actually grown in the ground. This could be somewhat offset by having people use their compost as fertilizer but still. Again I don't know a whole lot about what I'm talking about so correct me if I'm wrong.

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