San Mateo County, CA Noise Ordinances: Decibel Limits (2026)
Key Facts
- Governing sections
- Ordinance Code §§ 4.88.330, 4.88.340
- Daytime cap, sustained noise
- 55 dBA at homes/schools
- Nighttime cap, sustained noise
- 50 dBA at homes/schools
- Peak momentary cap
- 75 dBA day / 70 dBA night
- Music/tone-noise reduction
- minus 5 dBA
- Construction exemption hours
- 7 a.m.-6 p.m. weekdays
- Violation classification
- misdemeanor, separate offense per day
Summary
In unincorporated San Mateo County, exterior noise reaching a home, school, hospital, church or library cannot exceed the numeric limits in Table I of Code Section 4.88.330: as low as 50 dBA at night and 55 dBA by day for sustained sound, rising to 70-75 dBA only for the briefest spikes. The Health Officer enforces the limits, and violations are misdemeanors.
4.88.330 - Exterior noise standards. It is unlawful for any Person at any location within the unincorporated area of the County to create any noise... which causes the exterior noise level when measured at any single or multiple family residence, school, hospital, church, public library situated in either the incorporated or unincorporated area to exceed the noise level standards as set forth in Table I following... Category 1, 30 [cumulative minutes], Daytime 55, Nighttime 50; Category 2, 15, 60, 55; Category 3, 5, 65, 60; Category 4, 1, 70, 65; Category 5, 0, 75, 70.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 47).
Full Breakdown
); Category 2 (15 minutes) caps at 60/55; Category 3 (5 minutes) at 65/60; Category 4 (1 minute) at 70/65; and Category 5, any duration at all, at 75/70. Each standard is reduced by 5 dBA for simple-tone noise or noise consisting primarily of speech or music, and every category floats upward in 5 dBA increments if background noise already exceeds it. 340 sets parallel interior standards inside a receiving dwelling unit, topping out at 55 dBA daytime and 50 dBA nighttime. m. Saturdays, and all day Sunday, Thanksgiving and Christmas.
Anyone who cannot meet a standard may apply to the Noise Board of Review, which is the county Planning Commission, for a variance with a $50 filing fee; the Board must rule within 30 days, a granted variance runs no more than one year, and the applicant may appeal the Board's decision to the Board of Supervisors within 15 days.
Violations & Fines
Violating any exterior or interior noise standard in Chapter 4.88 is a misdemeanor under Section 4.88.460, with each day the violation continues charged as a separate offense. Primary enforcement responsibility belongs to the Health Officer under Section 4.88.470, and the County Sheriff may also enforce the chapter within its area of responsibility under the interdepartmental noise-enforcement procedures adopted under Section 4.88.310.
Frequently Asked Questions
What is San Mateo County's nighttime noise limit?
Does the county noise ordinance reach into incorporated cities?
Can construction legally exceed the noise limits?
How do I get a variance from the noise standards?
Sources & Official References
Other rules in San Mateo County
California rules heatmap·Compare San Mateo County to another location·View the California noise ordinances overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.