The Falls Church City Council has approved the addition of "accessory dwelling units," commonly called granny flats, in its larger residential districts.

The decision last week made Falls Church the first local jurisdiction to formally approve granny flats, which have been promoted as a revenue source for the elderly and single-parent families who may be having difficulty paying mortgages and rising property-tax bills. About 23 percent of Falls Church homeowners are at least 65 years old and 24 percent, mostly women, are single parents.

Under the Falls Church ordinance, accessory units could be added to 1,255 homes, about one-fourth of the city's residential units, city planner Stephen Leeper said.

The Falls Church ordinance requires that the units have a separate bath, kitchen and outside entrance and may not be added to town houses or multifamily dwellings. The regulation takes effect at the end of April.

The measure, proposed for study by the council a year ago, was recommended by a panel of citizen groups and the city planning department. The planning commission recommended against it in a 4-to-3 vote, with members saying they were concerned the need for granny flats had not been proven and they might alter the residential character of some neighborhoods. The council last week overrode the planning commission, with a 5-to-2 vote.

In January, Fairfax County gave preliminary approval to accessory units but has yet to take final action. Under the Fairfax measure, such flats would be available only to the elderly and handicapped. County officials have estimated the restrictions would initially permit rental units in only about a dozen homes.

In Fairfax County, the measure would permit granny flats only in houses at least 5 years old. The Falls Church measure, however, would allow the accessory units to be added to both old and new houses.