Building Permits in Marin County, CA

A small accessory concrete slab (walkway, patio pad, small equipment pad) of 200 square feet or less at grade is exempt from a building permit. Larger slabs that will support a future structure or are part of a building foundation fall under the building permit. Stormwater BMPs may apply per CALGreen for impervious surfaces over a threshold.

Kentfield, etc.), a freestanding deck not more than 30 inches above grade and not more than 200 square feet is exempt from a building permit under 2025 CRC R105.2. County zoning setbacks still apply. If your parcel is in incorporated Larkspur (94904 partial overlap), use the City of Larkspur Building Division at (415) 927-5038. WUI/VHFHSZ parcels: Chapter 7A ignition-resistant material may still apply to deck materials and surrounding 5-ft ember zone.

Fences 7 feet or less are exempt from a building permit under 2025 CRC R105.2. County zoning regulates fence height (typically 4 feet front-yard, 6 feet rear/side) and setbacks. VHFHSZ defensible space rules under PRC 4291 may restrict combustible fences within 5 feet of structures (use non-combustible material in ember zone).

An at-grade uncovered concrete or paver patio is exempt from a building permit. Adding a cover, roof, or screen enclosure turns the covered area into an accessory structure requiring a building permit. CALGreen and county zoning may regulate impervious surface coverage and stormwater runoff.

A retaining wall 4 feet or less measured from bottom of footing to top of wall, without surcharge, is exempt from a building permit under 2025 CRC R105.2. Drainage and erosion control remain the owner's responsibility. Bay Area seismic and Marin's hillside terrain require careful drainage design.