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PRI's Environmental News Magazine

Green Roofs

Air Date: Week of August 27, 1999

In heavily-paved urban areas, a good downpour can quickly overwhelm a municipal sewer system. But an ancient building technique that's popular in Europe suggests a way to alleviate the problem: add a touch of green to the roof. Roof-top vegetation provides insulation, cooling and waterproofing; and it can help prevent runoff, too. Here in the U.S., the idea is just catching on. Steve talks with Tom Liptan, a storm water specialist for Portland, Oregon. Two years ago Mr. Liptan built a green roof on top of his garage.

Transcript

CURWOOD: It's Living on Earth. I'm Steve Curwood. When it rains, the saying goes, it pours. And in cities it usually pours off the roof. In heavily-paved urban areas, a good downpour can quickly overwhelm a municipal sewer system. But an ancient building technique that's popular in Europe suggests a way to alleviate the problem: add a touch of green to the roof. Rooftop vegetation provides insulation, cooling, and waterproofing, and it can help prevent runoff, too. Several German cities already require so-called green roofs on all new commercial buildings. Here in the US, the idea is just catching on, and we found one of its proponents. Tom Lipton is a storm water specialist for Portland, Oregon, a city where sewer overflows are common. Two years ago Mr. Lipton built a green roof on the top of his garage. He told me he got the idea one evening standing at his kitchen sink.

LIPTON: One day my wife and I were washing the dishes, and I picked up this new soap, dishwashing soap that she had purchased and I was looking at the label. It was a really nice label, and it was from Belgium. And as I read it, down at the bottom it said that this Belgian factory had the largest grass roof in the world. And it had an 800 number on it, and I thought well why don't I call it? And then something clicked in my mind and I thought: roof gardens and storm water. So I made a phone call to the company representative who was in California, and they sent me some information, and that's where I first started seeing information that said yes, these roof tops actually hold a lot of water, and the water that does flow off them is dramatically slowed down. Its runoff rate is much slower than just a regular roof.

CURWOOD: So what exactly does this thing look like?

LIPTON: Right now, from the sidewalk, you would see the dried flowers from the plants when they bloomed back in April, May, and June, it was blooming. And so, those flower stalks are still on the plants. I'm trying not to garden this roof top, I'm trying to let it go and see what happens. And it changes. It's a very dynamic roof system in the sense that it changes with the seasons. The plants turn different colors, sort of a mosaic of color with the different types of seed and with red and yellow and green. And this time of year is when it gets a little bit brown, which sort of represents this characteristic we have in the west of the dry summers. And that's beautiful, too.

CURWOOD: Now, this roof is really a research project for you, right?

LIPTON: Yes, it is, right.

CURWOOD: And so, what kind of data have you gotten so far?

LIPTON: Two pieces of information. One is that I've been monitoring the amount of water that has -- the amount of rainfall we've had. So I have a rain gauge. And then I just literally measure the total volume of water that has run off, and then I subtract the difference, and that's the amount that stays on the roof.

CURWOOD: Okay, so tell us: how much stays on the roof?

LIPTON: Well, it varies. And to give you an idea, I actually have a chart that I've been keeping. So, for instance, last August we had about an inch and a half of rainfall and it held about 95% of that rainfall.

CURWOOD: Because it's pretty dry in August.

LIPTON: Right. Then in October, we had about 6-1/2 inches of rainfall and it held, percentage-wise, about 30% of that. So then it started dropping off dramatically as we -- because once we hit October, November, December, January, and February, it was so wet, and we did have a higher than normal rainfall. But it was down at around 30, as low as 15% in January.

CURWOOD: Now, Europeans do this. In some cases on a large industrial
scale, you've discovered. Now, why do you think it's taking so long for it to catch on in this country?

LIPTON: I guess because it seems like a wild idea. It doesn't seem like it's practical. But yet, what I found now is that it appears more and more practical every day. And the other is, I don't think we in the United States considered this building technique as a storm water management tool, and that's probably the key, I think. Because in Europe it appears from most of the literature that they were definitely looking at this as a means of holding water and keeping it out of their combined sewer systems. For instance, in Europe they will, in many cities, give you a discount on your sewer bill. So you pay less sewage fee than the person who doesn't have this type of roof system. As a matter of fact, we're thinking if that's something we might try to develop here for the city is a way to compensate for that, if the owner has this type of roof.

CURWOOD: Let's say someone listening to us now says, "Okay, I think I'll build myself one of these." How do they go about it?

LIPTON: Well, I have a book at the office that is -- it's a do-it-yourself, small-scale roof gardening book. It's written in German so I can't read any of it (Curwood laughs) but it has a lot of pictures.

CURWOOD: Okay.

LIPTON: I think it would be -- I would encourage people to one, definitely look at the structure of their building and get some professional advice. I know a little bit about structural -- structures on a small scale, so I felt very comfortable in looking at doing the work on mine. But they should check with someone who knows structure. They need to either know about plants themselves and soil, or have someone help them with that. So there's a whole range of issues with plant materials, soils, the structure of the building that they might be interested in doing this to.

CURWOOD: Tom Lipton is a storm water specialist for the city of Portland, Oregon. Thank you so much for taking this time with us.

LIPTON: Well, thank you, Steve.

 

 

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