San Mateo County, CA Noise Ordinances: Industrial Noise (2026)

Stationary industrial and commercial noise sources in the unincorporated county are exactly the kind of fixed noise the Chapter 4.88 standards are designed to address. Under Section 4.88.330, the exterior noise level produced by such operations, measured at any affected residence, school, hospital, church or public library, may not exceed the Table I limits for the relevant daytime (7 a.m.-10 p.m.) or nighttime (10 p.m.-7 a.m.) period, with stricter limits for longer-duration noise and a not-to-exceed ceiling. Section 4.88.350 separately prohibits unreasonably loud, unnecessary or unusual noise that disturbs the peace, weighing the noise level against background noise, the zoning of the area from which the noise emanates and on which it impacts, the number of persons affected and the time of day. Section 4.88.360 grants narrow exemptions - for example, emergency equipment and certain agricultural operations (the latter generally limited to 7:00 a.m.-8:00 p.m. for mobile sources), and construction/grading only within set hours - so routine industrial operations cannot rely on those carve-outs at night.