'Granny units' for quick new housing

A trend is building in many American cities to allow homeowners to add on a rental unit. California, for instance, has extended a July 1 legislative deadline calling for local governments to adopt guidelines for homeowners who want to sprout ''granny units.'' The new deadline, now Dec. 31, was set so as to get maximum community participation.

Advocates of the add-on-unit idea say these will not only provide more affordable housing quickly but will also tend to help revitalize commercial activity in neighborhood real estate. Instead of going to a wide-open, anything-goes plan, many local planning authorities are studying various guidelines for granny-addition construction.

Proposals under consideration include provisions that:

* In-law apartments be rented only to the elderly or to the handicapped.

* Such property carry a deed restriction based on occupancy.

* Units be re-registered annually, and should be allowed only on property with 45,000 square feet of ground.

* Enclosed parking spaces be considered.

* Possible maximum size of add-on units be 750 square feet.

Builders say costs of additional units are usually about half that of new construction and can at this time be financed with equity home loans. A San Francisco-based, nonprofit conservation organization, People for Open Spaces, says that today on the West Coast, a major second unit as an add-on could be built for about $24,000 with the owner acting as general contractor.