Strolling through Portland, Oregon, one can see something surprising – roofs covered not with black asphalt shingles, but plants! A green roof – or an ecoroof – is made by first sealing the top of a building with a waterproof membrane to prevent leaks. Then a drainage layer is covered with soil, low-growing grasses and plants.


Green roofs absorb rain and reduce stormwater runoff, which in turn reduces the amount of chemicals and debris flowing into storm drains and out into local rivers and streams.

Chomowicz: “Fifty percent of the rain that falls on the roof never leaves the roof. And it really shows just how well these roofs work in terms of managing stormwater. The rest will run off the roof into the storm system but it will do it at a much, much slower rate.”

That’s Amy Chomowicz, the Ecoroof Program Administrator for Portland, which has more than six hundred buildings with ecoroofs.

Green roofs also save energy, as they can be 60 to 90 degrees cooler than black asphalt roofs that bake in the sun. And they provide habitat for bees, butterflies, and birds, restoring nature in the concrete jungle.

Reporting credit: ChavoBart Digital Media.
Photo: Example of a “green” roof (source: City of Portland Environmental Services).

More Resources
2013 Annual Green Roof Industry Survey
Portland’s Ecoroof Program Leadership Award at the 2013 International Green Roof Congress
An introductory video about Ecoroofs
Ecoroof fact sheet

A regular contributor to Yale Climate Connections since 2012, David Appell, Ph.D., is a freelance writer living in Salem, Oregon, specializing in the physical sciences, technology, and the environment. His...