Spring 2011

Studying the Benefits of Accessory Dwelling Units

Left, 1415 Allston Way; right, 1843 Berryman Street.
Left, 1415 Allston Way; right, 1843 Berryman Street.

Students and faculty at the College of Environmental Design have long designed creative approaches to increasing density in residential neighborhoods. But California’s implementation of SB 375, the Sustainable Communities and Climate Protection Act of 2008, is putting new pressure on communities to support infill development. So the timing could not be more perfect for the Institute of Urban and Regional Development’s Center for Community Innovation to study small-scale infill, specifically, the potential impact of an accessory dwelling unit strategy in the East Bay.

In-law units, or accessory dwelling units (ADUs), are self-contained, smaller living units on the lot of a single-family home. They can be either attached to the primary house, such as an above-the-garage unit or a basement unit, or, as is more typical in Berkeley, an independent cottage or carriage-house. They are an easy way to provide homeowners with flexible space for a home office or an on-site caregiver, additional rental income, or a space for elderly family members to remain in a family environment. In short, they offer the kind of flexibility that has become imperative in today’s world to accommodate fluctuating work schedules and alternative family arrangements.

Left, 2601 Derby Street; right, 1822 Virginia Street.
Left, 2601 Derby Street; right, 1822 Virginia Street.

The concept, often termed “invisible density” or “distributed housing,” is hardly a new idea — indeed, the practice of building a supplementary unit behind a main house has been prevalent in Berkeley and throughout the East Bay for over a century. But ADUs particularly fit the context of Berkeley’s flatlands, with their historically “blue-collar urban form.” These “minimal-bungalow” districts are characterized by neat regularity, uniform land use, and little change — making them ideal for ADU development. Developers in the 1910s and 1920s widened the lots from 25 feet to 40 feet, created uniform setbacks, and supplied single backyard garages in order to maintain lower densities in the neighborhood. CED Professor Paul Groth argues that this uniformity was meant to create more predictable land values and erase the visual evidence of class struggle seen in more mixed-use, informal districts by imposing middle-class values. But today, the wide lots and historic garages provide an opportunity for infill.

ADUs provide benefits for both society and individuals. As infill development, they make efficient and “green” use of existing infrastructure and help increase densities to levels at which transit becomes viable — yet with lower costs and quicker permitting processes than for larger, multi-family building types. Because ADUs tend to be relatively small and their amenities modest, they provide more affordable housing options (at less than one-third of the cost of comparable units in multi-family buildings). Oftentimes, these units are the only rental housing available in older, predominantly single-family neighborhoods, making it possible for people from all walks of life to live in the area. Yet, they also significantly improve the value of the property, in essence constituting an asset-building strategy for homeowners.

Left, Ventura Avenue at Marin Avenue; right, Edwards Street at Channing Way.
Left, Ventura Avenue at Marin Avenue; right, Edwards Street at Channing Way.

The Center for Community Innovation (CCI) is studying the potential to add detached ADUs on single-family lots in Berkeley and other East Bay cities as a way to moderately increase density, provide homeowners with extra income, and create affordable rental units — all while preserving the character of existing neighborhoods. Based solely on lot size requirements and the square footage of existing structures, tens of thousands of homeowners could construct ADUs. However, a closer look at city regulations reveals other barriers to scaling up the strategy. Most importantly, most cities require the property to provide space for two parking spots — one for the existing single-family home, and another for the ADU.

CCI is studying ways to relax these off-street parking requirements without contributing to neighborhood parking problems. In neighborhoods near Bay Area Rapid Transit (BART) stations, residents may not need to own a car, particularly if car sharing is available. Car sharing services like Zipcar and City CarShare allow members to access a car whenever they need one, without the hassle of owning — and parking — their own individual vehicles. By finding ways to integrate ADU development with transit ridership and car sharing, CCI hopes to facilitate the development of sustainable, affordable housing options in Berkeley’s neighborhoods. The study will be available by fall 2011.

Virginia Street.
Virginia Street.

But the biggest barrier is perhaps psychological. Homeowners regularly fight neighbors’ plans to alter their property. Though they may object to a building’s form and appearance, or the loss of privacy in their own backyards, more likely they are concerned about the impacts of increased car parking on the street. Sensing the objections of the neighbors, homeowners balk at improving their own property, even if it makes financial sense. And ironically, the homeowners who would most benefit from the improvement — whether because they live in older small houses or because their family income is unstable — are often themselves reluctant or fearful of assuming the new financial obligation.

The best way to overcome these fears is by demonstrating the benefits and value of ADUs. Luckily, a CED class on sustainable design, taught by Ashok Gadgil from the Lawrence Berkeley National Lab, was the genesis of a demonstration project — a model cottage in my West Berkeley backyard. Students analyzed zoning requirements and developed preliminary designs for a net-zero-energy cottage. Energy efficiency measures, such as well-insulated walls, reduce the building’s electricity usage, while a new solar photovoltaic system removes the cottage and the main house from the electricity grid. Built for $100,000, and rented for $1,200 per month, the cottage not only makes financial sense but also demonstrates how careful design can make a small space beautiful. That there is significant interest in the idea became apparent during our open house in January 2011, which attracted almost 500 people.

Net-zero-energy affordable unit located in author Karen Chapple’s backyard.
Net-zero-energy affordable unit located in author Karen Chapple’s backyard.

The next step is to demonstrate the value of scaling up an ADU strategy. The CCI study is analyzing the potential impact of constructing thousands of these units in the East Bay. In economic terms, the impact is significant. A $100,000 ADU generates an additional $80,000 of indirect and induced spending in the economy, and if most purchases are made locally, each ADU creates one year-long local job. Thus, construction of 4,000 ADUs locally would mean 4,000 local jobs. New property taxes could feed city coffers. And, each net-zero-energy ADU creates energy savings that impact the local economy. If households save $25 in energy costs each month, construction of 4,000 ADUs could thus mean an additional $1.8 million spent on local goods and services each year. If the new households are clustered, they may be able to help the region’s struggling retail corridors become more viable.

Other impacts we are evaluating pertain more to resource use, particularly in California. Distributed generation will reduce dependence on utility-produced energy. Incorporation of greywater systems — for instance, recycling water for irrigation needs — at a large scale could reduce pressure on California’s water supply. And clustered demand for alternative transportation modes could make local car share and transit systems more sustainable.

Ultimately, though, an academic study will not persuade policymakers to scale up this strategy. What should happen next is another demonstration project, this time on a larger scale. What if the local utility, water, housing, and transit agencies, working closely with the cities, sponsored a pilot program that incentivizes homeowners to build 100 ADUs in the region? Such a pilot could help overcome homeowner inertia, and would also demonstrate the benefits of scale to the agencies themselves. The precedent for this exists in the pilot energy-efficiency programs that cities, funded by federal stimulus dollars, have been offering to local homeowners. CED and its research centers look forward to providing a venue that spurs this conversation — and results in a more sustainable Bay Area and California.