When Do You Need a Survey?

Here's an uncomfortable fact: your fence is probably not on your property line. Fences get built by whoever felt like building them, decades ago, wherever was convenient. Two or three feet of drift is common. Now recall Module 2: your ADU may legally sit just 4 feet from the true line. See the problem?

What a survey is. A licensed land surveyor locates your legal property corners from recorded data and physical monuments, marks them, and (for a boundary survey) produces a stamped drawing of the true lines. Cost: typically $2K–$5K. It is the only authoritative answer to "where does my property end?" — not the fence, not the county GIS map (those parcel lines are approximations), not the neighbor's confident memory.

When you clearly need one:

• The ADU is designed at or near the 4-foot setbacks (most ADUs!)
• Fences, hedges, or driveways make the boundary genuinely ambiguous
• Your city requires a survey with ADU submittals (many do)
• A hillside or drainage situation needs precise topography (a topographic survey adds elevation data — often bundled)
• Any hint of boundary disagreement with a neighbor

When you can sometimes skip it: the ADU sits far from every line — a conversion in the middle of the lot, or a placement with 15+ feet of margin everywhere. Skipping is a judgment call your designer should make explicitly, not by omission.

The horror story it prevents (a real genre, not a hypothetical): ADU built 4 feet from the fence; survey later reveals the fence was 3 feet onto the neighbor's land; the building now encroaches, and the remedies — easement negotiations, lawsuits, or partial demolition — all cost more than every survey in the neighborhood combined. Against that, $3K is not an expense. It's the cheapest insurance in this entire course.