written by:
October 26, 2011

Project Manager Brad Liljequist chronicles the building of the zHome, a ten-unit townhome in Issaquah, Washington—the first multifamily zero-energy community in the United States. Part 4: A new approach to stormwater management.


Water and salmon are iconic in the maritime Northwest. The Puget Sound basin has for decades been a hub of innovation in stormwater management, with a goal of protecting these icons. Recently, a movement has been afoot to change how stormwater is managed. In past years, stormwater for new development was typically collected in large vaults or ponds and then released at a set rate into local streams and lakes. While this strategy has had success in reducing impact to local water bodies, it requires large infrastructure, and also is not always effective in limiting runoff impacts.

zHome embodies a new stormwater management strategy called "low impact development," which takes a more site-driven approach, where water is detained and returned to the ground right on site. Our stormwater benchmark requires that the same amount of rainfall be reintroduced to the ground as fell there in the site’s original forested state. We employed a number of strategies to achieve this. 

zHome also has been "Salmon-Safe certified," the first residential project in Washington State to achieve this standard. Salmon-Safe’s mission is to "transform land management practices so Pacific salmon can thrive in West Coast watersheds." This independent certification ensures that zHome’s stormwater and landscape management systems are ecologically sound and safe to aquatic resources. Click through the slideshow to learn more about zHome's strategy, and click here to watch a video about the cachement system.

As part of our education program, we’ve created extensive education signage, designed by <a href="http://www.softfirmstudios.net/">SoftFirm</a>. This sign shows the flow of water through the site.
As part of our education program, we’ve created extensive education signage, designed by SoftFirm. This sign shows the flow of water through the site.
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Water from the sloped roofs is collected into cisterns. Each home has its own cistern—1,100 gallons for smaller homes, and 1,700 gallons for larger. This water is used to flush toilets, wash clothes, and for outside spigots. Water use is reduced by 20 gal
Water from the sloped roofs is collected into cisterns. Each home has its own cistern—1,100 gallons for smaller homes, and 1,700 gallons for larger. This water is used to flush toilets, wash clothes, and for outside spigots. Water use is reduced by 20 gallons per person per day throughout the project. This photo is of one of the 1,100 gallon cisterns, left exposed for educational purposes. The remaining cisterns are underground.
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Water from the cisterns are then pumped into a holding tank inside the house (the blue tank). The regulator to the right of the tank sends a signal to the pump when to add more water to the tank, which is maintained at 55 psi. When a draw occurs on the ta
Water from the cisterns are then pumped into a holding tank inside the house (the blue tank). The regulator to the right of the tank sends a signal to the pump when to add more water to the tank, which is maintained at 55 psi. When a draw occurs on the tank, it flows through a five and a one micron filter (above the tank), so the water coming out is very clean.
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Water entering the cisterns is pre-cleaned by a leaf filter (the angled mesh at the downspout outfall). The water then fills a first flush diverter, which is the tube just after the main intake. This tube has a float in it, and a small outlet at the botto
Water entering the cisterns is pre-cleaned by a leaf filter (the angled mesh at the downspout outfall). The water then fills a first flush diverter, which is the tube just after the main intake. This tube has a float in it, and a small outlet at the bottom. About 3-4 gallons of water enters this tube first, with the float rising to the top—then plugging the hole at the top and bypassing the water into the main fill tube, which fills the cistern. This ensures the initial flush of water containing debris, pollen, dirt, etc., does not enter the cistern. To the right of the fill assembly is a hose spigot. Below the spigot is a fill port. Here residents can fill their cisterns when they run dry during the summer months. The cisterns are expected to run dry during this time. To ensure 100% rainwater for these uses would have required a doubling of cistern size.
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This small remote device tells the homeowner how much water is in the cistern (it’s full!).
This small remote device tells the homeowner how much water is in the cistern (it’s full!).
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Once the cistern is full, the water is then piped into the community raingarden, shown here. Water fills the raingarden, which is open at the bottom, and filters directly into the ground. The soils in the area are very permeable, making them great candida
Once the cistern is full, the water is then piped into the community raingarden, shown here. Water fills the raingarden, which is open at the bottom, and filters directly into the ground. The soils in the area are very permeable, making them great candidates for this type of stormwater design.
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zHome employs other low impact stormwater strategies. Thick layers of compost tilled into the dirt ensures native landscaping will be able to survive with minimal or no irrigation. Many of these plants were harvested and relocated from a future developmen
zHome employs other low impact stormwater strategies. Thick layers of compost tilled into the dirt ensures native landscaping will be able to survive with minimal or no irrigation. Many of these plants were harvested and relocated from a future development parcel about a half-mile from the site. This compost is from Cedar Grove, which recycles area food waste. Local food and yard waste is composted only about five miles from the compost site, and is returned here as part of the landscaping. Waste = food!
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The woonerf (a plaza shared by vehicles and people) at the edge of the site is built with pervious concrete, which allows stormwater to percolate directly into the ground—another low-impact stormwater strategy.
The woonerf (a plaza shared by vehicles and people) at the edge of the site is built with pervious concrete, which allows stormwater to percolate directly into the ground—another low-impact stormwater strategy.
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Sun falls on the zHome green roof. Green roofs are becoming a more common approach in the Northwest to slow flows off of flat roofs. It also looks great, too (this is the view out of one of the zHome dining room windows).
Sun falls on the zHome green roof. Green roofs are becoming a more common approach in the Northwest to slow flows off of flat roofs. It also looks great, too (this is the view out of one of the zHome dining room windows).
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Nick and Kyle, resident strongmen, feel good about their reuse of found boulders in site landscaping. Both are bow hunters and avid outdoorsmen.<br /><br /><p><strong>Click </strong><a href="http://www.dwell.com/people/brad-liljequist.html?tab=articles&am
Nick and Kyle, resident strongmen, feel good about their reuse of found boulders in site landscaping. Both are bow hunters and avid outdoorsmen.

Click here to read past installemts of Building A Zero-Energy Community.

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As part of our education program, we’ve created extensive education signage, designed by <a href="http://www.softfirmstudios.net/">SoftFirm</a>. This sign shows the flow of water through the site.
As part of our education program, we’ve created extensive education signage, designed by SoftFirm. This sign shows the flow of water through the site.

Click here to read past installemts of Building A Zero-Energy Community.

Don't miss a word of Dwell! Download our FREE app from iTunes, friend us on Facebook, or follow us on Twitter!

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