Grading & Drainage: Redwood City vs San Mateo
How do grading & drainage rules compare between Redwood City, CA and San Mateo, CA?
Redwood City and San Mateo have similar restriction levels.
Redwood City, CA
San Mateo County
San Mateo County requires a Grading Permit from Planning & Building for projects involving more than 250 cubic yards of cut and/or fill, or any grading on slopes over 20%, or grading within 100 ft of a watercourse. Drainage design must direct runoff away from structures and must not adversely redirect water onto neighboring properties. Retaining walls over 4 feet in height need separate engineering and permits. Pre-site erosion-control and tree-protection inspection may be required.
View full Redwood City rules →San Mateo, CA
San Mateo County
Grading and drainage in San Mateo are regulated under the city's building code (Title 23) and the NPDES Municipal Permit. Projects requiring grading permits must submit drainage plans. All projects creating or replacing 5,000+ square feet of impervious surface must meet stormwater treatment requirements.
View full San Mateo rules →Key Facts Comparison
| Fact | Redwood City | San Mateo |
|---|---|---|
| Permit Threshold | 250 cu yd or 20% slope | - |
| Watercourse Buffer | 100 ft triggers permit | - |
| Retaining Walls | Over 4 ft needs permit | - |
| Geotech | Required on steep/fill sites | - |
| Compaction | 90-95% standard | - |
| Permit | - | Required for grading exceeding thresholds |
| Erosion Plan | - | Required for all site disturbance |
| Stormwater | - | Treatment at 5,000+ sq ft impervious |
| Code Reference | - | SMMC Title 23 |
| Public Works | - | 650-522-7300 |
Highlighted rows indicate differences between cities.
Redwood City FAQ
How do I know if my property exceeds 20% slope?
20% slope equals a rise of 2 feet over 10 feet of horizontal distance. On a topographic survey, contours closer together than 5 ft apart at 1-ft intervals typically indicate slopes over 20%. County GIS has slope layers, but for permit determination you'll need a licensed surveyor's topographic map of your parcel.
Can I level my backyard myself with a rented skid steer?
If the cumulative cut AND fill total stays under 250 cubic yards, no grading permit is required provided slopes remain under 20% and you're not near a creek. But you still must not redirect drainage onto neighbors, must maintain erosion controls during work, and may not create cut/fill over 3 ft in height. When in doubt, call Planning at (650) 363-4161.
San Mateo FAQ
Do I need a grading permit in San Mateo?
Yes, for earthwork exceeding thresholds established in Title 23. All site disturbance also requires an Erosion and Sediment Control Plan.
What stormwater requirements apply to my project?
Projects creating or replacing 5,000+ square feet of impervious surface must meet stormwater treatment requirements under the city's NPDES permit.
Who reviews drainage plans?
The Public Works Department reviews grading and drainage plans. Contact them at 650-522-7300.
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