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.