Quiet hours in San Mateo County, CA — also called the noise ordinance, nighttime noise rules, or residential quiet time — define the hours during which excessive noise is prohibited.
San Mateo County unincorporated areas are governed by noise ordinance Chapter 4.88. Daytime hours are 7 AM–10 PM; nighttime 10 PM–7 AM. Exterior noise limits range from 55–75 dBA daytime and 50–70 dBA nighttime based on duration.
San Mateo County Ordinance Code Chapter 4.88 (Noise Control) establishes tiered exterior noise standards for unincorporated areas. Noise is unlawful if it exceeds: 55 dBA daytime/50 dBA nighttime (cumulative 30 min/hr), 60/55 dBA (15 min/hr), 65/60 dBA (5 min/hr), 70/65 dBA (1 min/hr), or 75/70 dBA (any instant). If ambient exceeds the standard, the standard adjusts in 5 dBA increments. Noise levels for simple tone sounds (speech, music) are reduced 5 dBA. Chapter 4.88.350 also prohibits any unreasonably loud, unnecessary, or unusual noise disturbing neighborhood peace.
First offense warning or citation. Fines typically $100 to $500. Repeat violations may result in misdemeanor charges.
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See how San Mateo County's quiet hours rules stack up against other locations.
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