Marin County, CA Building Safety: Anti-Mansionization (2026)

060 targets exactly the kind of oversized rebuild that drives mansionization complaints: it applies to new residential construction on a vacant lot, to a "substantial remodel" on a property with a 25 percent or greater average slope, and to a substantial remodel on a lot that does not meet the minimum lot area requirement, where "substantial" means an addition of 25 percent or more of existing floor area. 30) maximum adjusted FAR is a hard ceiling unless a property owner obtains discretionary review under the floor area guidelines in Appendix B of the Tamalpais Community Plan.

5-foot ceiling, accessory dwelling units, the combined total of detached accessory structures of 120 square feet or more (excluding garages), window boxes or bays under 18 inches above the finished floor or projecting more than 3 feet, garage space over 400 square feet on lots of 6,000 square feet or less, garage space over 480 square feet on larger lots, and covered porches or entryways that could later be enclosed. For a brand-new house on a vacant lot exceeding 25 percent average slope, the Code imposes an absolute backstop: the maximum adjusted floor area is whichever is smaller of 7,000 square feet or the FAR-based number, no matter how large the parcel is. The standard was adopted by Ord. No. 3577 (2012) and amended by Ord. No. 42 is the gate through which any deviation must pass.