A California home with a changing character

Michael Sands is a Bay Area architect who, like most of his clients these days, keeps reworking his own home to make it more complete, convenient, and livable.

''For at least the last two years,'' he says, ''most of my jobs have been remodels, because people cannot afford to buy or build another home. So we are revamping kitchens and bathrooms, adding bedrooms, and sometimes shifting the order of rooms around so that the house can function more efficiently. A lot of rethinking is going on about living spaces, and architects are helping people analyze their needs and then adjust their present housing to fit them.''

Mr. Sands cites his own home as a case in point. Five years ago he designed a new house in Corte Madera for himself; his wife, Cindy; and their three youngsters. He and Mrs. Sands decided they would invest in a contemporary ''shell,'' which would accommodate all their present requirements and include potential for future phasing in of other specific areas.

They drew up a long-range master plan that included family needs for the foreseeable future, and then determined what they would develop for immediate use. They agreed that a relatively open plan would allow the house to grow and change as the family grew and changed - and would also allow each living area to borrow visual space from those adjoining it.

Already the downstairs study has changed character three times. From the original den-office for dad, it became an all-purpose playroom for the children. Last year it was requisitioned by 13-year-old daughter Kirstin, who wanted a room of her own downstairs away from younger brothers Ian and Kort.

That move meant it was time to build in the reading balcony over the living room, as foreseen in the master plan. This small angled area, big enough to sleep a guest, serves as a regular and cozy retreat for family members who want to curl up with a book or look at television.

Although the house is relatively small -2,100 square feet - it contains four bedrooms, a full pantry, a little sewing room off the kitchen for Mrs. Sands (''so I could sew and watch the cooking at the same time''), and a first-floor laundry room with an outside door that can double as a mud room.

Their next project, also already in the master plan, is a downstairs studio-cum-office that can be shared by both Mr. and Mrs. Sands. And, somewhere in the future, the unfinished downstairs space exists for a possible mother-in-law unit.

''When prices come down,'' says Mr. Sands, ''we'll probably add the active solar equipment to the house that we specified in the master plan. Right now we are using our southern exposure and a big main skylight as passive solar heat collectors.''

The house appears to be perched in treetops on a high ridge overlooking San Francisco Bay. The view is so expansive that, unbroken, the architect felt it could be overwhelming. His solution was to place windows so they would frame certain choice segments of the view.

The many-angled house, with its various floor and ceiling levels, is redwood on the outside and Douglas fir woodwork and white sheetrock walls on the inside.

Mr. Sands places the cost of the house, when built, at $35 a square foot, plus another $10 a square foot for his own labor in finishing it off. At the time, this was about half the going rate of $60 to $85 a square foot for custom houses of this type. He worked the shape and volumes to make his small house appear much bigger, and he also economized on the siding and flooring he used.

He also explains that the use of built-ins all over the house contributes a great deal to its sense of well-utilized space. One project this year has been the addition of built-ins to all the children's rooms. Another project recently completed was the location several months ago of an antique pine and tile mantel to finish off the fireplace in the parents'own bedroom.

''We love the search to find just the right things to add,'' Mr. Sands says, ''and we love antiquing, so little by little the house assumes more quality and character.''

In furnishings, the Sands love mixing big bold Marimekko fabrics, stretched on frames, with modern oak furniture and Early American antiques. They have a collection of genuine, old oil lamps; an old ship's lantern is a prominent accessory. They love their California country kitchen, and their prize possessions there are an old Hoosier cabinet, an antique wall telephone, and a well-used butcher block on legs. Mrs. Sands has made the rag rugs for all the rooms in the house.

The Sands are proving that if you start with a good shell and a long-range plan, you can keep adding and improving as your budget allows. ''We don't see any end to it,'' Mr. Sands says. ''We just see it going on and on as long as we live in the house. But we like it that way. We think change is important.''