Currently, the biggest house on Santa Clara County's tax rolls is 19,951 square feet.

``When is it enough?'' said resident Robin Robison. ``We've seen it inch up: 20, 25, 30'' thousand square feet.

More generous than several affluent towns, Los Altos Hills allows people to develop 6,000 square feet for every flat acre of land. A 12,000-square-foot home could fit on two acres, 18,000 on three acres and so on. Woodside, Los Gatos and Palo Alto generally cap main residences at 6,000 square feet no matter how large the lot.

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