El Niño prep: Harvest rain from your roof
Rob D. Brodman / Sunset Publishing

Rob D. Brodman / Sunset Publishing

Santa Fe permaculture landscape designer Nate Downey knows the drill: Do a rain dance for weeks, then rejoice as it falls before cursing the flooding and erosion it causes. “My thought has always been, How can we turn that erosion problem into a rainwater-harvesting solution?” he says. He found the answer in an unlikely place: the roof. With a record El Niño on the horizon, we asked him to tell us more.

Thomas J. Story / Sunset Publishing

Sunset: Why should we pay attention to more than permeable paving in the landscape?

Downey: I’m all about the impermeable surfaces: roofs, patios, and driveways. But especially roofs—they’re so clean! And rain comes off of them with such force. It’s such a resource waiting to be captured. No matter where you live in the West, there’s a rainy season. It might be winter in the dry-summer Mediterranean sections, or monsoons in the Southwest, but everyone’s got a roof.

Sunset: What are you doing to spread the roof gospel?

Downey: I have a Roofwater Calculator on my website that allows you to type in your address and see how much rain comes down from your roof in an average year. It’s a way to make this resource real, and really wake people up.

Thomas J. Story / Sunset Publishing

Sunset: How do people turn their roofs into water-harvesting machines? 

Downey: There are different ways. It can be an active system with a cistern and pump. Or it can be a passive one—having a downspout that leads into a trench. I fill the trench with any type of porous rock, essentially creating an underground sponge that stores water. Traditionally, pumice is used. But I prefer a more sustainable material called Growstone, a product made from recycled glass, developed in Santa Fe and manufactured in Albuquerque.

Sunset: Are all roofs created equal?

Downey: Pitched metal roofs are better than flat tar-and-gravel ones. But really, there are not a lot of bad roofs out there.

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