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The Case for Accessory Dwelling Units
Julia Levitt, 24 May 10

You don't always need an entire city block or vacant lot to create impact with urban infill. In residential urban neighborhoods, the collective potential of a hundred backyards adds up…to prime retrofit real estate.

The solution: ADUs, also called "granny flats" or "mother-in-law apartments," are small dwellings built within or next to an existing home. Garage conversions, basement apartments and coach houses have been fairly common models for decades. But prefab housing options are making it possible in some cities to find a prototype, customize the details, and have the sleek, modern unit ready for renters within months.

Cities including Santa Cruz, Seattle and Vancouver have passed new codes that allow these kinds of dwellings in single-family areas. Increasingly, these local governments are even providing design and administrative support to boost production. Santa Cruz's award-winning Accessory Dwelling Unit Development Program, created in 2005, provides pre-approved, architect-designed prototypes for compact living spaces so homeowners don't need to start from scratch to create a well-designed small home. The program also offers online tutorials on permitting, building and becoming a landlord.

The Alley Flat Initiative in Austin, Texas envisions accessory dwelling units as a leading strategy for providing new housing in Austin's East Side. Architecture students at the University of Texas's Center for Sustainable Development have developed prototype ADU designs that incorporate cutting-edge green technologies like rooftop solar power, rainwater catchment, daylighting and passive ventilation.

Because no new land must be purchased, ADUs cost less to build than new homes on undeveloped lots, and thus can be rented at an affordable price while still earning profit for the homeowner. The result: affordable housing options that blend right into the surrounding neighborhood…and that are built at virtually no cost to taxpayers.

Photograph of UTCSD student design-build team in front of Alley Flat 2: Lydia Street via The Alley Flat Initiative.

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I was the sustainability staff member on Vancouver's EcoDensity Initiative, which eventually passed our laneway housing policies--and I argued against it the whole time.

We have all heard that density is green, but why? Ed Mazria says it is the buildings, and indeed, a study done for EcoDensity found that super-green mid and high-rises could cut about 95% of the energy used in operations. The other big thing is transportation of course, and it is here that infill helps.

But for that building energy use, most infill does nothing. All it does is add another horribly inefficient single family home leaking energy through its walls and roof.

And what else does density do? The planner in North Vancouver found that granny suites meant the City would have to dig up and enlarge all the storm sewers. The additional impervious surfaces for parking and housing sent more water into the storm drains. North Van was able to require stormwater management on site to avoid re-piping.

But it is not just stormwater, it is food and energy and waste and grey water. We all know that we are facing a world of diminishing fossil fuels, which will require much more effective use of energy. In many cases, the most effective use of energy is to walk over and do something yourself. And that means we need way more space for food growing, water collecting, waste composting and energy generation in close proximity to our homes or groups of homes.

I think there is a sweet spot of urban form that will balance effective use of urban space. It will never make sense to grow grain in the city when it stores so well and is easily shipped by rail. But similarly, it will never make sense to ship in lettuce from any further away than your doorstep. I would love to see somebody model this. My gut suggests we start looking at three-story midrise buildings, spaced twice as far apart as they are now.

Posted by: Ruben on 24 May 10

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