An accessory dwelling may be a useful home away from home

January 29, 2011

If you live in a subdivision home, there's a good chance your rear yard could accommodate an accessory dwelling for one or even two people. Visualize a tiny cottage behind your house occupied by a teenager, an adult son or daughter who has returned home, a grandparent, a child-care provider, a housekeeper or a rent-paying tenant. But what are the pros and cons of this idea?

To answer this question and show that this is an idea whose time has come, the University of California at Berkeley reports that a real-world test of the accessory dwelling concept is underway. A prefabricated, 420-square-foot cottage has been built in the Berkeley back yard of Karen Chapple, associate professor of city and regional planning.

Designed as a "green" prototype, the cottage is constructed with sustainable lumber, recycled metal roofing, well-insulated walls, non-volatile paint and a gas on-demand water heater.

Currently rented to a pair of firefighters and their young son, the cottage has a tight but high-ceilinged living room, a narrow kitchen with granite countertops and a miniature dishwasher, a dining-office nook, a conventional 5-by-7 bathroom, and a sleeping loft reached via a ship's ladder. A shed-roofed porch spans the gable-ended entry facade.

Chapple, director of the Center for Community Innovation, leads a study funded by the University of California Transportation Center "to determine how many accessory homes could be built around five Bay Area Rapid Transit stations, and how they might affect the local economy." Berkeley has as many as 4,000 backyard cottage infill sites, according to the study's preliminary findings. A metropolitan area could have hundreds of thousands of such sites.

Chapple and her study team envision infill accessory dwellings as a potentially cost-effective, sustainable densification strategy for existing communities, a strategy that could augment transit usage and viability while expanding and diversifying affordable-housing opportunities. And it's theoretically a strategy applicable anywhere in the United States.

But as logical and beneficial as the strategy seems, scaling it up for widespread implementation faces legal, technical, economic and political obstacles, whether in California or metropolitan Washington.

l Regulatory impediments. Few zoning ordinances allow accessory dwelling units on lots in one-family residential zones, where neighborhood population and dwelling unit density are purposely limited. Parking regulations also can be problematic, since most city and county zoning ordinances mandate at least one on-site parking space for each one-family dwelling unit. Many subdivision lots do not have room for an extra car.

l Physical site challenges. Unfavorable topographic conditions and poor drainage can complicate construction of a backyard cottage. Mature trees and other valuable landscaping worth protecting can be in the way. Transporting construction equipment, prefabricated components and building materials into a back yard may be troublesome if side yards are too narrow or obstructed. Installing new utility lines running across a back yard to the cottage can be difficult and expensive, especially if water and sewer mains are not in an easement or alley at the rear of the lot.

l Fire protection. If firetruck access to a back yard is impeded or impossible, fire marshals, who always have the final say, may deny issuance of a building permit for an accessory dwelling behind a house.

l Construction costs. The cost of an accessory dwelling can vary widely, depending on design, site conditions and location. Karen Chapple's cottage reportedly cost $100,000, about $250 per square foot and more than the square-foot cost of production homes in many areas of the United States. However, her cottage is a prototype. Standardization, factory prefabrication and volume production can greatly reduce dwelling structure cost, but not the cost of site preparation and foundation work, which always must be customized.

l Social and political resistance. Here emerges the literal manifestation of NIMBY (not in my back yard) thinking expressed by homeowners skeptical about or strongly opposed to accessory dwellings. Reasons for resistance are many: loss of backyard privacy for abutting lots and homes, more traffic and unwanted competition for on-street parking, anxiety about an influx of neighborhood residents of different socioeconomic status, objections to increased density, and worries about adverse effects on property values.

As tough as coping with legal, technical and economic challenges may be, overcoming social and political resistance is even more daunting. Indeed the NIMBY attitude of home-owning voters can easily dissuade elected officials from implementing regulatory changes that would allow accessory dwellings.

Producing compact, functional backyard cottage designs that are green and affordable is not the problem. The real problem is how to convince homeowners that their fears are unfounded and that creating accessory dwellings is a feasible, worthwhile idea. And the only way to accomplish this is to persuasively demonstrate the value and effectiveness of the idea, which is what the university in Berkeley is trying to do.

Roger K. Lewis is a practicing architect and a professor emeritus of arch- itecture at the University of Maryland.

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