February 15, 2018

Will the next roof you design be stormwater-sustainable?

Since prehistoric humans first stretched an animal skin between two overhead branches, one of the principal goals of architecture has been diverting rainwater. Keeping the rain out—and everything inside dry—is a common attribute of structures ranging from thatch-roofed huts to 100,000-seat domed stadiums.

For most of human history, however, we didn’t give much thought to what happened to stormwater after it ran off our roofs. One school of thought was, “The farther away, the better,” and entire cities were built to divert rain from rooftops to drainpipes to sewers to rivers and, finally, to distant oceans.

Today, with drought becoming a more or less permanent condition in many areas of the world, builders are exploring more sustainable ways to collect and retain stormwater where it falls.

Stormwater retention replenishes local aquifers, reduces flooding and helps protect waterways from contaminated runoff. Here are some ways architects, designers and engineers are making stormwater collection a stylish, sustainable component of modern commercial design.

Bring your roofs to life

The most obvious way to retain stormwater is to keep it on the roof where it falls. Living roofs, also called green roofs, do exactly that. A living roof is exactly what it sounds like—a roof that’s completely or partially covered with soil and vegetation. The vegetation soaks up a portion of every rainfall before it even hits the building’s drainpipes.

In addition to stormwater retention, green roofs can also help reduce energy costs by keeping a building’s interior cooler. Plus, the cooling power of water evaporating from rooftop vegetation helps reduce the “heat island effect” that can make city temperatures as much as 10 degrees hotter in the summer.

A living roof can be scaled to almost any commercial building. Among the more notable examples: the new Microsoft campus in Mountain View, California, and Chicago City Hall. Chicago, in fact, has a city-wide green roof initiative that at last count boasted more than 500 living roofs with 5.5 million square feet of green coverage.

Make drainage dramatic

Whatever your roof can’t absorb has to be drained away, obviously. But that doesn’t mean your drains have to be boring.

The Indianapolis Zoo recently opened an open-air event pavilion that delightfully incorporates stormwater capture into the structure’s overall theme. A lush “rainforest” with 11 steel-framed “tree canopies” directs the runoff from 40,000 square feet of roofing into planting beds before it’s filtered through a water quality unit and held in a 14-foot-deep water detention bed.

The University of Southern California, meanwhile, built a state-of-the-art stormwater collection system into USC Village, its massive new housing, retail and dining development. While the City of Los Angeles requires 85% of rainwater to be captured onsite, the USC Village system retains up to 95% of its runoff—while functioning completely out of sight.

57 hidden drains capture runoff from the 15-acre site, routing it to six-foot-diameter drywells up to 60 feet deep. A rock filtration system removes contaminants and debris from the water, which seeps through another thick layer of alluvium before finally reaching the aquifer.

Aim for zero

Architects, designers and engineers concerned about sustainability are paying closer attention to the Zero Net New Water standard for large public and private facilities.

A Zero Net New Water facility is one that consumes no more water from original sources than it returns. Collecting and storing rainwater—for landscaping and other non-potable uses—is one of the most important parts of the equation buildings use to achieve this standard.

If you’re already specifying water-saving plumbing fixtures for your commercial building projects, a modern stormwater collection system can help your next project achieve Zero Net New Water status.

That’s a sustainability standard that might have pleased our prehistoric ancestors—at least the ones who were clever enough to rig their animal-skin roofs to collect drinking water.

From the 1906 invention of the Royal® Flushometer to today’s automatic fixtures, Sloan’s innovations have saved building owners billions of gallons of water. Want to know more? Talk to Sloan!

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