Verify Lot Requirements
Not every property qualifies for an ADU. Minimum lot sizes, coverage limits, and other zoning rules determine whether you can build—and how big. Verify these requirements before investing in plans.
Quick Summary
Time needed
1-2 hours
Cost
$0-$500
You'll need
Property survey
Key Requirements to Verify
1Minimum Lot Size
Many jurisdictions require a minimum lot size to build an ADU. Typical ranges:
- • Urban areas: 4,000-6,000 sq ft minimum
- • Suburban areas: 5,000-10,000 sq ft minimum
- • Rural areas: Often no minimum or very large (1+ acre)
Good news: Many states have eliminated minimum lot size requirements for ADUs. California, for example, now allows ADUs on any lot with a single-family home.
2Lot Coverage Limits
The percentage of your lot that can be covered by structures (all buildings combined):
- • Typical limits: 40-60% of total lot area
- • Calculate: (Main house + garage + ADU footprint) ÷ lot size
- • Covered patios and carports may count
Example Calculation:
- • Lot size: 8,000 sq ft
- • Max coverage (50%): 4,000 sq ft
- • Existing footprint: 2,500 sq ft
- • Available for ADU: 1,500 sq ft footprint
3Floor Area Ratio (FAR)
FAR limits total floor area (not just footprint) relative to lot size:
- • FAR = Total floor area ÷ Lot size
- • Common limits: 0.4 to 0.6 for residential
- • Includes all floors of all structures
FAR Example:
- • Lot size: 8,000 sq ft, FAR limit: 0.5
- • Max total floor area: 4,000 sq ft
- • Existing home: 2,800 sq ft (both floors)
- • Available for ADU: 1,200 sq ft living space
4Owner Occupancy Requirements
Some jurisdictions require the owner to live in either the main house or ADU:
- • Strict: Owner must live in main house or ADU
- • Relaxed: No occupancy requirement
- • Time-limited: Must occupy for first X years
Investment impact: Owner occupancy rules affect whether you can rent both units or sell your home while keeping the ADU as a rental.
How to Find Your Lot Information
County Assessor Records
Search your county assessor's website with your address. You'll find lot size, existing structure sizes, and often zoning information. This is free and instant.
Property Survey
Your closing documents should include a survey showing exact lot dimensions, easements, and structure locations. If you can't find it, contact your title company or order a new survey ($300-$600).
GIS/Parcel Maps
Most counties offer online GIS (Geographic Information System) maps showing parcels, zoning, setbacks, and sometimes even aerial measurements. Search "[your county] GIS map."
Measure Your Existing Structures
If records seem inaccurate, measure your home's footprint yourself. Include garage, covered patios, and any other roofed structures. Use a tape measure and calculate length × width for each area.
Does Your Lot Qualify?
Answer these questions to assess feasibility:
If you answered "no" to any question, discuss with your planning department. There may be exceptions, variances, or recent rule changes that help.
Frequently Asked Questions
My lot is too small—any options?
Check if state law overrides local minimums. You might also qualify for a Junior ADU (JADU)—a smaller unit created within the existing home footprint, often 500 sq ft or less.
What if I'm already at max lot coverage?
Consider converting existing space (garage, basement) instead of building new. Some jurisdictions also allow two-story ADUs that have a small footprint but more floor area.
Do pool houses or sheds count toward coverage?
Usually yes for covered structures. Uncovered decks, patios, and pools typically don't count toward lot coverage but check local rules—they vary.
Ready for the Next Step?
Once you've confirmed your lot qualifies, the next step is understanding setback requirements—how close to property lines you can build.