Converting a single-family home's surplus space into separate living quarters can be a viable option to building anew if you need an extra home or some rental income.

Conversions, however, are not a task for the faint of heart.

Commonly called "granny flats," the conversions are also known as "mother-in-law suites," "bachelor pads," and "echo homes," but are officially called accessory or auxiliary dwelling units -- ADUs.

ADUs can be converted attics or basements, carved out of a wing of a large home or, at the extreme, built from scratch in the back yard or elsewhere on the property.

The construction work transforms a section of the home into a self-contained home, apartment- or studio-like unit, often with a private entrance to living and sleeping quarters, a kitchen or kitchenette and sometimes separate power, water and sewage lines.

The dwellings can provide accommodations for other family members, including young adult children making a transition to school, independence or back home, as well as older parents who may be in need of home health care. Au pairs, nannies, other domestic laborers and, occasionally, exchange students may use such quarters. Owners also may rent them out for extra income.

In more recent years, ADUs have become a physical manifestation of the Internet's revolution in decentralization. A live-work unit allows entrepreneurs to incubate their own business, while working at home.

In a growing number of communities, ADUs are one answer to housing shortages and affordability issues.

California's housing shortage, for example, is forcing communities to relax zoning laws to permit conversions of detached garages, or larger "carriage houses." Likewise Hawaii, Massachusetts and other states are rewriting zoning laws to ease ADU development.

However, many communities' zoning laws may ban or severely restrict the special housing units.

If you are considering an ADU, your local planning department should be your first stop. It can tell you if ADUs are allowed in your neighborhood or even on your block and if there are certain restrictions to square footage, style or location on your property.

Even where ADUs are permitted, your neighbors are likely to exhibit NIMBYism (for, "not-in-my-back-yard") and pick apart favorable zoning laws until they find a provision that works against you.

If you create an ADU without approval and it's discovered later, building officials could force you to rip it out or tear it down.

Where ADUs are allowed, the actual conversion construction work is relatively easy and much like any other major remodeling job -- with a few major caveats.

Garages and other attached or detached structures pose special construction dilemmas because they were originally constructed without the same systems and structural support as the main house.

Garages, for example, were built to house cars and storables, not people. Often built on a concrete slab without a vapor barrier, a garage or carriage house could yield moisture problems once you introduce heating and cooling. Extending the existing heating, power and water lines to a converted garage isn't as easy as running a phone or cable line. In some areas earthquakes and storms create special structural engineering concerns.

Don't forget tax and insurance implications.

Some locales consider ADUs new homes against which a separate property tax is levied.

In any event, when you add livable square footage to your home, your property value could rise which likely will increase your existing property tax bill and home owner insurance premiums.

More Resources:

• The U.S. Department Of Housing and Urban Affairs "Regulatory Barriers Clearing House" Web site page offers a host of related and relevant publications about ADUs.

• AARP offers "Accessory Dwelling Units: Model State Act and Local Ordinance," a look at ADUs regulatory barriers.

Published: April 7, 2004

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Broderick Perkins parlayed a career in old-school journalism into a contemporary digital news service that really hits home. The award-winning consumer journalist, originally from Wilmington, DE, is founder, publisher and executive editor of the bootstrap DeadlineNews Group, a Silicon Valley-based editorial content and consulting service specializing in residential real estate, consumer news and related editorial consulting services. The DeadlineNews Group includes the website, DeadlineNews.com, offering real estate editorial content and consulting services, and its back shop, the Deadline Newsroom, an open house on news that really hits home. Perkins obtained his formal journalism education from University of Delaware and a journalism boot camp, the Institute of Journalism Education at the University of California-Berkeley. He went on to 20 years of service as a daily newspaper journalist at the Wilmington, DE News Journal and San Jose, CA Mercury News. Perkins covered housing on the San Jose Mercury News reporting team which earned a General News Reporting Pulitzer Prize in 1989 for coverage of the Loma Prieta earthquake. He has also produced real estate, consumer and small business content for the Wall Street Journal, Los Angeles Times, RealtyTimes.com, Nolo.com, Better Homes and Gardens, the National Association of Realtors, Homestore/Move and Intuit/Quicken among more than three dozen publications. In addition to managing the DeadlineNews Group, Perkins most recently served as chief editorial consultant for Nolo's Essential Guide To Buying Your First Home, Nolo, and writes real estate television scripts for RealtyTimes.com.