ADU builders
Land survey for an ADU: when you need one
By the HyreADU research desk. Last checked .
The short answer
A land survey for an ADU locates your lot lines and, if needed, the slope of the ground.
You need one when the ADU sits close to a lot line, when the fence may not be on the line, or when the lot slopes.
In California the by-right setback can be as small as four feet, so a few feet of error matters.
Boundary vs topographic survey
A boundary survey finds and marks your property lines. A topographic survey maps the ground levels, trees and structures. A sloped lot or a design with drainage questions usually needs both.
Why setbacks make it matter
California bars any rule that prevents an ADU of at least 800 square feet with four-foot side and rear setbacks (Gov. Code § 66321(b)(3)), and requires approval of a detached unit at those setbacks (Gov. Code § 66323).
Building four feet from a line you guessed is a risk. Fences are often not on the property line. A plan checker accepts a survey, not a memory.
Who can do one
Land surveying in California is licensed work. Check the license on the Board for Professional Engineers, Land Surveyors, and Geologists site. Ask whether the survey will be recorded and whether corners will be marked on the ground.
What to do next: read the questions to ask an ADU builder, check what decides ADU cost, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.
Get ADU optionsQuestions
Can I use the assessor’s map instead?
Assessor maps are for tax, not for building lines. Use them as a start only.
Does every ADU need a survey?
No. An interior conversion often does not. A detached unit near a line usually should.
Who orders the survey?
Usually you or your designer, before drawings start.
What if the survey shows my fence is wrong?
Talk to a lawyer before you build or move anything. HyreADU does not give legal advice.
Sources
- Gov. Code § 66321 (size and height floors). Checked September 5, 2026.
- Gov. Code § 66323 (by-right ADUs, utility connections). Checked September 5, 2026.
- California Board for Professional Engineers, Land Surveyors, and Geologists, license lookup. Checked October 27, 2026.
HyreADU is a publisher. It does not design, permit or build ADUs, has no partner builders, and gives no legal, tax or engineering advice. Rules vary by state and city; California rules are labeled as such.