Green Roofs

Green roofs help offset carbon dioxide and purify air in urban areas while lowering utility bills.

One of the best ways to make a building greener is to literally make it greener.  CAP has the story.

Green roofs, or living roofs, offer a number of important benefits not only to the environment but also to property owners. And while many might think of green roofs as exclusively in the purview of commercial property, home installation can be both practical and economical.

Green roofs are created by using rooftop space to plant a layer of grasses, shrubs, flowers, and other forms of flora and greenery. Typically, green roofs begin with an insulation layer, followed by a waterproof barrier, then by the organic material used to grow the plants. Construction and maintenance of green roofs is inexpensive and they can also last far longer than traditional roofs if the appropriate plants are used.

Although green roofs have been catching on as a part of the growing trend to make our cities and buildings more sustainable, they are in fact nothing new. People around the world built their houses with roofs made of sod or grass for hundreds of years. Though those houses are now seen as relics of antiquity, their construction serves as useful inspiration to guide the design of the sustainable houses of tomorrow.

The most obvious benefits of living roofs come from the fact that rooftop planting greatly increases the available amount of green space in any urban or suburban environment. Increasing the number of plants in these neighborhoods helps offset the amount of carbon dioxide emitted from these hubs of human activity. Furthermore, plants can effectively filter air and remove other harmful pollutants. In fact, a study from Michigan State found that installing green roofs should be an important component of our strategy to combat climate change.

Urban spaces typically create what is called a “heat island,” a locale that is noticeably warmer than surrounding areas because of human activity and a lack of greenery. Green roofs, however, can abate local warming trends by cooling and humidifying the surrounding air. If used en masse, it’s quite feasible to think that green roofs could make significant contributions to cleaning and cooling the air we breathe.

Green roofs can also lower pollution by decreasing the amount of water that runs off into drainage systems. Whereas rainwater usually collects in our water supply after picking up pollutants and contaminants along the way, green roofs store water and immediately recycle it for plant growth. Roofing houses with living material serves as a natural mechanism to recycle rainwater, circumventing the need for treatment.

Homeowners can also benefit from installing green roofs. Properly constructed living roofs are excellent insulators and can therefore decrease heating and cooling costs. This not only leaves more money in the pocketbooks of those paying utilities but also makes homes more environmentally friendly by reducing the amount of energy used for climate control.

Last, but not least, green roofs provide an exciting opportunity to change the aesthetic dynamic of homes, neighborhoods, and communities. Rooftops can become landscapes covered in a diverse array of flowers, grasses, shrubs””all of which can be sustained by the local climate. Adding to the portfolio of green space in neighborhoods can beautify communities, improving life for those who live there and visit.

If you need to redo your roof””or are simply looking for a way to make your home more environmentally friendly””installing a green roof can be a wise decision. You can save money on your utilities, help the environment, and beautify your home all at the same time. Best of all, with the availability of online guides, it’s possible for do-it-yourselfers to undertake a fun project and save money on construction costs. Or if you’d prefer not to, contact local contractors to see who has experience in the green roofing business.

– A CAP cross-post, which Joe Romm has updated.  I also switched out their picture.

JR:  For most homeowners, without an easily accessed roof, I’d suggest a cool roof — white or using reflective paint — see “Cool roofs save money, save energy, cut pollution and directly reduce warming!

This “urban heat island mitigation” (UHIM) may well be the single most cost-effective energy and climate strategy (see background here plus “White roofs are the trillion-dollar solution“).

16 Responses to Green Roofs

  1. Jfix says:

    How do you maintain them without risking life and limb?

  2. Tim says:

    Not to be a wet blanket, but mowing my roof would seem be a dangerous proposition. Watering it doesn’t sound like a lot of fun either.

  3. Jeffrey Davis says:

    If we had the luxury of starting from scratch, green roofs, berming and hyper-insulating would definitely be 3 preferred technologies.

  4. joyce says:

    The photo chosen is misleading. The vast majority of green roofs do not have grass on them. They have climate specific succulents or groundcovers that do not need much care after established, and roofs are engineered for the extra weight of the specific lightweight soil used.

    Yes, it would be rediculous to mow your roof! I laughed at that photo used. It looks like someone just let their roof rot. It reminds me of what my husband says: “We have a green roof!”–referring to the moss that has taken over our garage. (We live in the PNW)

    [JR: I have updated the post and image.]

  5. Mike Roddy says:

    Whoever said that green roofs are practical and economical has never built a house. You need a strong membrane, allowance for drainage and debris, and possibly beefed up trusses, which is a tough retrofit.

    We should still do it, but encouraging people to not worry and wing it will lead to disasters. New construction in earthquake zones and high rainfall areas presents special challenges. People need to do their homework.

  6. David Smith says:

    Tim @ #1 – Green roofs are generally designed with plants that grow slowly and can survive in a broad range of water conditions. Plants sellected take a couple of years to mature and cover the roof reducing anual maintenance considerably.

    A point not mentioned in the post is that direct sunlight is the primary cause of degradation of the waterproof surface on a roof and covering the membrane will extend the life expectancy of the roof almost indefinately. Only the perimeter of the roof is exposed causing normal deterioration and requiring eventual replacement.

  7. Sou says:

    Where do you put the solar panels for power and hot water? How well does it stand up to heavy rain (like 70mm/hour plus)?

  8. bob mills says:

    Joyce @ #4: where do you get your information?

    fyi, the vast majority of green roofs in Scandanavian countries — and there are hundreds of thousands of them — look exactly like the original picture.

    and Mike @ #5, they’ve been doing it that way for hundreds of years, and you see modern houses constructed this way as well, which from the inside look just like any house here; well, except for odd Scandi ideas about showers… ;)

  9. Adam R. says:

    @bob mills:
    and Mike @ #5, they’ve been doing it that way for hundreds of years, and you see modern houses constructed this way as well,

    No doubt, but Mike’s points are still valid. One must not willy-nilly load a few extra tons on top of an existing design and expect all to be well. Green roofs are a fine idea, but not without careful structural engineering.

  10. Joan Savage says:

    In Syracuse NY, retrofits of flat top buildings with green roofs are part of an initiative to reduce the rate of storm run off, not necessarily its total volume.

    A pulse of rain of an inch an hour falling onto smooth surfaces can quickly overburden the Syracuse storm drain capacity, which is partially connected into the sewage treatment system. If this works, we can save billions on reconstructing and remodeling the “gray” parts of the system.

    It’s obvious that Syracuse is dependent on continuing moderate weather, or all bets are off.

  11. lizardo says:

    I live in a mostly rural NC county and our local community college included a green roof in it’s new sustainable curriculum classroom building that opened last fall. News release and pix here:

    It also uses solar hot water for HW and for radiant floor heating, captured water for flushing toilets, and a lot more. I mention this because we are not an affluent county but the savings going forward made this possible, plus a forward looking county board and CC administration. So the fact that it serves as a demonstration is simply a plus. (The sustainable curriculum includes organic agriculture, green building, natural chef program, alternative energy, with AAS degree offering…)

    And re the point about not loading up a roof– I’ve always wondered about those NYC rooftop gardens.

  12. GFW says:

    I have aspirations of a “green deck” covering half my driveway. My roof on the other hand is where the solar panels will go (when solar is cheap enough to be cost-effective near Seattle – I’m guessing around 2016-2018).

    Aside to Bob, I *like* Scandinavian showers :-)
    (Adjustable height, temperature control marked in degrees… they know how to live)

  13. Green roofs are not a new phenomenon. In fact, in the following short video, a junior high school student shows us how to build one!

  14. No one is commenting on Joe’s note near the bottom of the page, so I will. His comment is

    “JR: For most homeowners, without an easily accessed roof, I’d suggest a cool roof — white or using reflective paint — see ‘Cool roofs save money, save energy, cut pollution and directly reduce warming!'”

    For some parameters, like temperature and direct carbon emissions from the roof surface, white roofs are better than green roofs. For other parameters, like delaying peak runoff discharge and humidity from plant respiration, green roofs are superior. As far as loading on a roof, white reflective paint is much lighter, cheaper, and more effective in lowering the temperature of the roof. As it lowers the temperature, artificial cooling is less necessary.

    As a result, Secretary Chu advocates a movement to white roofs and lighter road surfaces nationwide. This is one important and cheap measure to mitigate the built environment’s use of energy. It has the further benefit of fighting the urban heat island effect. So, neighbors benefit from white roofs on a commercial building, too. For the majority of people who can’t afford to upgrade the strength of their roof support for a green roof, choose a lighter color of roofing or a reflective roof material next time you reroof. Your energy bill will go down.

  15. ken levenson says:

    a green roof is quite possibly the very last thing a climate concerned person should consider doing – speaks to lifestyle/fashion perhaps…
    much better to insulate, make air tight and properly ventilate…if you want to really raise the bar, go for passive house level sustainability –

  16. Jay Alt says:

    15) Ken. I understand the logic of that and I think that’s probably the best course for homeowners. But the problems and challenges to greening our lifestyles are many. Chicago mayor Richard Daley decided to implement Green/Cool City projects after a deadly 90s heatwave. He began it all by planting a green roof on top of city hall. That ran against the advice of most environmental leaders, who wanted projects with more impact. But Daley knew his politics and he knew how to get the public’s attention. It was soon evident to everyone that this was a great choice and a powerful symbol.