Can I Build an ADU
on My Chino Lot?

Step 1: Confirm Which City Your Parcel Is In

This is the non-obvious first step for Chino-area properties. The 91710 zip code is largely City of Chino. The 91709 zip code is largely City of Chino Hills. But zip codes don't exactly match city boundaries. The definitive check: San Bernardino County's parcel data at assessor.sbcounty.gov. Enter your APN (on your property tax bill) and confirm the City field. Alternatively, if your tax bill shows the City of Chino Hills as the taxing entity, you're in Chino Hills. If it shows City of Chino, you're in City of Chino. The planning departments are at different addresses and have entirely different application processes.

Step 2: VHFHSZ Fire Zone Status (Chino Hills)

For City of Chino Hills parcels, the fire zone check comes before lot dimensions, before coverage calculation, before anything else. A VHFHSZ designation changes the construction specification, the permit plan requirements, and the cost budget. Check at: osfm.fire.ca.gov/divisions/wildfire-prevention-planning-research/wildland-hazards-building-codes/fire-hazard-severity-zones-maps/ — enter your address and confirm whether you're in a VHFHSZ. We verify this during the site visit. If you're in a VHFHSZ, your ADU plans must include Chapter 7A fire-resistant construction specifications or they'll receive a first-round plan check correction.

Step 3: Slope Grade and Geotechnical Feasibility (Chino Hills Hillside)

For Chino Hills lots with visible slope, assess buildable flat area before finalizing any ADU location. A 15,000 sf Chino Hills lot with 25% average slope may have only 3,000–5,000 sf of genuinely buildable flat area. The remaining area may require expensive grading, retaining walls, and engineered foundations before construction can begin. A topographic survey ($1,500–$3,000) quantifies the actual buildable area. A geotechnical investigation ($3,500–$7,000) quantifies the soil bearing capacity and slope stability. Both are warranted before significant design investment on hillside lots.

Step 4: Identify Your Lot Dimensions and Coverage

City of Chino: Standard planned community lots 6,000–10,000 sf, 40% coverage limit. Coverage calculation same as other planned community markets — main house footprint subtracted from 40% of lot area gives available ADU coverage.

City of Chino Hills: Lots range from 6,500 sf (smaller The Preserve lots) to 25,000+ sf (hillside custom lots). Coverage limits are similar (typically 35–40%) but the effective buildable footprint is constrained by slope, grading requirements, and fire clearance setbacks on hillside parcels. Flat Chino Hills lots (The Preserve newer sections) calculate the same way as City of Chino.

California state law requires both cities to allow at least 800 sf regardless of coverage calculations — this protects eligibility on lots where coverage math might otherwise constrain the maximum ADU size.

Step 5: Confirm Water and Sewer Service

City of Chino: Chino Basin Water District or Inland Empire Utilities Agency (IEUA) serve different portions of the city. City sewer is standard. Call CBWD (909-628-1201) or IEUA (909-993-1600) to confirm which serves your parcel and request a connection feasibility assessment.

City of Chino Hills: Chino Hills Water District (909-597-2526) serves most of the city for domestic water. City sewer service is standard in developed areas. Carbon Canyon and some outlying areas may have private well or septic — verify before assuming city utilities.

Step 6: HOA Status

City of Chino Hills: 55% HOA probability. City of Chino: 35% HOA probability. Check your deed and recorded CC&Rs. For Chino Hills, the HOA identification affects both ARC review requirements and design standards. For City of Chino's The Preserve, the CC&Rs include specific ADU provisions adopted since 2022.