Mountain View, CA Building Safety: Anti-Mansionization (2026)

Mountain View doesn't label it mansionization control, but three pieces of Sec. 36.10.25 work together to stop a new second story from overwhelming a single-family block. Floor area ratio isn't a flat percentage: it runs on the formula FAR = 0.50 minus (0.00001 times lot area), so a 6,000-square-foot lot tops out at a 0.44 FAR while a 7,500-square-foot lot drops to 0.425, and any lot of 10,000 square feet or more is capped at a flat 0.40. Smaller lots, capped at 0.45 for lots of 5,000 square feet or less, get a comparatively higher percentage but a much smaller lot to apply it to, which keeps absolute square footage from ballooning on Mountain View's classic postwar lots.

Second, second-story walls have to sit further back from the side property lines than first-story walls do. Where a first story only needs 5 feet minimum per side, the second story on a standard lot needs at least 7 feet on the front half (with a 15-foot combined total) and 12 feet on the rear half, rising to a 10-foot minimum with a 25-foot combined total on the largest lots. That step-back keeps a boxy two-story addition from looming directly over a neighbor's side yard the way a flush first-story wall would. Third, second-story decks and balconies are restricted to the front and rear of the house, or the street side on a corner lot, and capped at a combined 150 square feet, so an uncovered deck can't substitute for floor area the FAR formula already limits.