San Diego County ADU Guide

San Marcos

Permit-ready detached, one-story plans may support the Express Plan path after property and program eligibility are confirmed.

Reviewed August 2026Official jurisdiction resource ↗
01 / Plan path

Choose the right production starting point.

Permit-ready detached, one-story plans may support the Express Plan path after property and program eligibility are confirmed.

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.

The local ordinance and selected plan establish available sizes; state-law minimum allowances remain relevant.

Specific plans, fire district requirements, utilities, drainage, and development fees can affect otherwise similar properties.
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.

  • Specific-plan area
  • Fire district
  • Utilities and easements
  • Slope and grading
  • Drainage and stormwater
04 / Consultant screen

Likely disciplines to evaluate.

  • Structural engineering
  • Title 24 energy documentation
  • Survey as required
  • Civil and geotechnical engineering when triggered

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.