Green Roofs

Photo © clarkmaxwell

Higher Ground

What if you could watch birds nesting and feeding in a grassy meadow from a high-rise roof in a major urban center? You could turn the roof over your head into the ground under their feet, and it’s not as uncommon as you might think. That’s just what the folks at the California Academy of Sciences did with the installation of a 2.5-acre green roof. To date, this living roof has hosted over 18 bird species (not counting fly-overs), including Brewer’s Blackbird, Anna’s Hummingbird, American Pipit, and Black Phoebe. Although just gaining popularity in North America, living roofs have been popular in Scandinavia for centuries (Copenhagen, the capital of Denmark, actually requires them for new construction!) Green roofs make the most sense for large, flat-roofed structures, especially those in urban landscapes; however, some people have successfully converted their small residential properties into living-roof showpieces.

Green Roof

This green roof adorns the top of City Hall, Chicago, Illinois.

Photo © Steven Vance

There are two basic kinds of green roof: intensive and extensive. Intensive green roofs resemble a traditional park or garden landscape, with perennials, grasses, and sometimes even trees or wetlands in their design. They typically cover smaller areas and require more maintenance than extensive green roofs. Extensive green roofs, on the other hand, may have a low-growing profile, perhaps with just a few species of sedum growing on them. They may cover thousands of square meters, but usually they are lower-maintenance. We’ve also seen largely extensive designs incorporate smaller areas of intensive gardens. Research suggests that green roofs can contribute to bird species habitat, even if the vegetation does not fulfill all habitat requirements. They can partially fulfill the habitat requirements of some species, in addition to restoring habitat connectivity for species like migrating birds 1.

More than 1,030 green roofs have been constructed in the United States 2, but many more are needed if we are to realize their full potential. Here are some of the advantages offered to buildings that support a living roof:

  • Additional habitat for birds and invertebrates
  • Insulation, resulting in reduced energy costs all year long
  • Visual interest and beauty
  • Space to grow your own food
  • Filtering of pollutants from rainwater and the air
  • Rainwater absorption, resulting in mitigation of storm surges
  • Possible financial incentives (like tax abatements, grants, low-interest loans, fast-track permitting, reduced permit fees, impermeable surface tax reduction, and others)
  • Longer lifespan than a traditional roof
  • Reduction of the urban heat island effect
The Lurie Garden

Chicago's Millennium Park is home to this 2.5-acre rooftop perennial garden.

Photo © UGArdener

The habitat above us

If you’re considering installing a green roof on your business or residential property, there are a few things you can do to make yours more bird-friendly. As with other habitat types, structural complexity is positively related to bird diversity and abundance. Area is also important to birds, so a large space or several clustered green roofs will improve your visibility to passing birds. Make sure your green roof has as many of the components of habitat (food, water, shelter, and freedom from danger) as possible; remember, this is your chance to design a habitat from the “ground” up, so thoughtful details designed for birds can go a long way towards your roof actually being used.

It’s easier to design habitat features during the planning stages than it is to add them in later, so carefully consider where your priorities lie, whether in low maintenance costs, high biodiversity, public use, education and/or demonstration (i.e., food gardens, natives, urban ecology, etc.), or retrofitting concerns. Some green roofs have seen over twice the species that others have, while some have hosted species not typically found in the surrounding landscape. In Chicago, monitoring efforts have revealed numerous native species, including an Olive-sided Flycatcher, Cape May Warbler, and a Philadelphia Vireo using City’s Hall green roof as habitat. You can help scientists determine which green roof attributes attract the most birds by following the lead of the California Academy of Sciences and reporting your observations to eBird. The potential to promote urban birds with living roof habitat—indeed, to actually inform future green roof design—is real!

Green roofs in cities are visited and used by birds more frequently than those located in the suburbs. 3

Perfect Pitch

If you have a pitched roof, then a living roof may not be an option for you (however, a flat-roofed shed or garage may be convertible). Any roof with a slope of 18 degrees or more isn’t suitable for growing vegetation because the planting base would eventually wash down-slope. Here are some alternative ways to get the benefits of a green roof without actually installing one (no, we don’t mean never cleaning your gutters):

Solar Array on a Roof

This solar array on the roof of a resort offers tourists green energy among other amenities.

Photo © Shell Vacations Hospitality

  1. Solar panels are a great option for pitched or steep roofs. They have few drawbacks and will make your home more energy independent. You can further increase the energy efficiency of your home by adding insulation and using programmable thermostats wherever possible.
  2. White roofs are a good alternative to solar panels and green roofs. The light color may help you use less energy to cool your house and mitigate the urban heat island effect. However, even if widely adopted, they may not be the climate-cooling solution scientists had hoped for 4. And if you live in a cold climate, white roofs may not pay off if you have more heating days than cooling days. But if this option works for you, check out this guide to “cool” roofs.
  3. Rain barrels are a quick project you can install this weekend, with the least investment of money and effort from you! Your gutters can direct rainwater into rain barrels positioned beneath your downspouts, allowing you to use the water to irrigate your garden and lawn, fill your bird bath, top off your swimming pool, or anything else you can reach with the hose.
  4. To increase the value of bird habitat around your home, reduce the amount of space allotted to lawns, eliminate your use of pesticides and herbicides, and plant natives densely in the short, medium, and tall structural horizons.
  5. An earth-sheltered building is one that is partially underground; therefore, the roof can be earthen and function like a green roof. By harnessing the thermal mass of the surrounding ground, this type of engineering offers good insulation plus additional green space around the home. They’re also visually interesting and compelling to curious visitors, so new-build businesses can attract green-minded customers with this design.

Map your green (or white) roof

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Photo ©

While logged into your map, click on the Toolshed and map your buildings.

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Photo ©

Then, complete the characteristics for the buildings by tell us what type of building it is, if it is a green roof, what the % of it is covered in greenery, and if the roof is painted white (for heat reflection) or not.

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