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Green & Main (4)


By October 2011 permeable pavers covered the parking lot, allowing water to be absorbed rather than being diverted to the storm sewer.

Behind the building a bioswale — a sloped drainage channel planted with native vegetation — can manage seven inches of rain (the 100-year flood level), trapping silt while the root systems of prairie grasses carry water deep into the ground to filter pollutants.

A 1,492-square-foot roof planted with 50 different sedum varieties can handle more precipitation. Eight wall-mounted storage tanks collect rainwater to use to wash off the parking lot and, when necessary, water the green roof.

“Green & Main is a great example of a site where they have worked hard to keep the water where it lands on the property,” says Jennifer Welch, an urban conservationist with the Polk County Soil & Water Conservation District.

“Otherwise, rainfall runs off streets, rooftops, and yards and picks up pollutants as it flows into the storm sewer and into our rivers, causing water pollution and flooding.”

Geothermal heating and cooling comes from eleven 300-foot-deep wells.

Sixteen solar panels on the roof will provide 20 to 25 percent of the building’s electrical needs. Daylight from a large skylight and multiple clerestory windows fills the interior, reducing the need for electricity.

The green roof provides natural insulation.

Low-density spray foam insulation was added to interior walls, creating a thickness that could support a second layer of windows inside the originals.

Halfhill estimates the completed Green & Main Pilot Project will be 76 percent more energy efficient than current national building standards.

During deconstruction the crew meticulously collected materials from the original structure for reuse — from floorboards, double-hung windows, and existing fixtures to metal pipes, lath, concrete, and asphalt.

They salvaged materials from razed buildings — floorboards from the school gymnasium in Cambridge, glass-block and crystal doorknobs from a building on the east side of Des Moines, structural 2x10 lumber from a garage in Sherman Hill, 1x6 shiplap lumber from Iowa barns (used for the subfloor), 8x8 barn beams (used for posts in the car port and solar arbor).

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