Flood Maps, Levees and Your Finished Grade

San Mateo has spent more than twenty years building its way out of the flood zone. The city added levee walls along San Mateo Creek, a tide gate and levee work at O’Neill Slough, and in 2023 finished the North Shoreview project with a new pump station and a 1,300-foot levee segment. A FEMA map revision that took effect October 11, 2024 removed about 1,600 addresses from the flood zone, covering properties in the North Central and North Shoreview neighborhoods.

Coming off the map doesn’t change how a flat lot drains. A yard that slopes toward the house will still pond against the foundation. Before we bid drainage or grading on the east side of town, we check the current FEMA map for the parcel, figure out where the water can go, and set the grade and pipe to carry it there. Our five signs your property needs drainage work is a good place to start.

Hillside Lots: San Mateo Goes by Slope

West of El Camino, San Mateo’s Site Development Code (Municipal Code Chapter 23.40) uses slope as the main trigger. Grading on slopes of 15 percent or more, or inside the required slope setbacks, needs a site development permit. On flatter ground, a permit is needed when grading covers more than 5,000 square feet and 185 cubic yards, or totals more than 550 cubic yards. On slopes of 25 percent or steeper in R1 and R2 zones, grading is limited to the driveway and the building foundation. Grading is also held to the dry season, April 15 to October 15, unless the city finds erosion control is adequate. Footing excavation, utility installations and storm drains in single-family areas are among the exemptions.

Digging Near San Mateo’s Protected Trees

San Mateo’s tree guidelines call for a tree protection plan from an ISA Certified Arborist when construction comes within ten times a protected tree’s trunk diameter. Closer in, within six times the diameter, below-grade work starts with a test excavation by air, water or hand, with the project arborist on site, and cutting roots inside that radius counts as major pruning that needs a permit. We dig those test pits by hand or with vacuum excavation.

San Mateo Project: Drainage and a New Parking Pad

On a residential job in San Mateo, we installed 150 linear feet of perforated drain pipe and 200 linear feet of solid drain pipe, hauled off 20 tons of material, and spread 20 tons of new aggregate base by hand to build a new parking pad. See the project. Just next door in Hillsborough, we hand-dug a PG&E electrical service relocation trench around several existing utilities, then backfilled it the same day after it passed PG&E inspection. Read about the Hillsborough job.

San Mateo Neighborhoods We Work In

We work across the city, from North Shoreview, Shoreview, North Central and East San Mateo to downtown, Sunnybrae, Hayward Park, Bay Meadows and Mariners Island, and up the hills through Baywood, Aragon, San Mateo Park, Beresford Park, Hillsdale and Laurelwood. Nearby, we also serve Hillsborough, Burlingame, Belmont, Foster City, Millbrae, Redwood City and South San Francisco.

San Mateo Excavation FAQ

Is my San Mateo property still in a flood zone?

Check FEMA’s current flood map for your address. The October 11, 2024 revision removed about 1,600 addresses, but not every parcel came off. We check the map before we design any drainage.

Do I need a permit to grade my hillside lot?

If the work is on a slope of 15 percent or more, or inside a slope setback, expect a site development permit. We’ll look at your plans and tell you what’s likely needed before we price it.

Does a drain line in my yard need a grading permit?

Storm drains in single-family areas are on the exemption list in San Mateo’s site development code. Other permits can still apply, so we confirm the scope before we start.

Plan Your San Mateo Project

Tell us what the water is doing on your lot, or send the plans for what you’re building. We’ll walk the site and send a clear written estimate. Request a free estimate