San Diego County ADU Guide

Unincorporated San Diego County

County standard dwelling plans may provide an Express Plan starting point. Site-specific completion and departmental review remain required.

Reviewed August 2026Official jurisdiction resource ↗
01 / Plan path

Choose the right production starting point.

County standard dwelling plans may provide an Express Plan starting point. Site-specific completion and departmental review remain required.

Express PlanStarting at $4,500

For a qualifying jurisdiction preapproved plan adapted into the property-specific architectural production set.

Custom PlanStarting at $6,500

For an original floor plan and architectural production set developed around the property and homeowner.

02 / Size + fee checkpoints

Size affects more than floor area.

Detached ADUs are commonly permitted up to 1,200 square feet. Attached-unit limits and other pathways must be confirmed against the primary dwelling and current County standards.

Standard County fees apply. Fire, Environmental Health, grading, drainage, and Public Works can materially affect the path and total cost.
500 SFConfirm school-fee assessment rules750 SFState impact-fee protection checkpoint1,000 SFTwo-bedroom state minimum allowance1,200 SFCommon local upper-range checkpoint
03 / Site conditions

Property conditions can change the path.

  • Community plan and zoning
  • Fire Hazard Severity Zone and fire district
  • Onsite wastewater or sewer service
  • Slope, grading, drainage, flood, and geologic conditions
  • Water district and access
04 / Consultant screen

Likely disciplines to evaluate.

  • Structural engineering
  • Title 24 energy documentation
  • Boundary and topographic survey
  • Civil and geotechnical engineering when grading is involved
  • Septic design and testing when applicable

Consultants are retained only when required by the property, design, or reviewing agency. Their proposals and coordination are separate from the architectural production fee unless stated otherwise in the agreement.

05 / Property-specific next step

Turn the guide into a preliminary project report.

Enter the address to screen jurisdiction, mapped constraints, likely agencies, drawing requirements, consultants, and the preliminary fee path.

Check the property →Email Bennett Design Studio →
Important: This guide is general planning information, not a zoning determination, permit approval, fee quote, or guarantee of feasibility. Current parcel records, adopted codes, agency interpretations, utility requirements, site investigation, and written agency confirmation control.