ADU Surveys in Mill Valley, CA

Mill Valley's ADU handout is built around thresholds a survey answers. A new detached ADU qualifies for building permit only review when it is sixteen feet or less in height, eight hundred square feet or less in gross floor area, and set back four feet or more from the side interior and rear property lines; attached units use twenty-five feet on the same square footage and setback terms. Overall ADU height is defined as the vertical distance from finished grade at the lowest exterior wall to the highest point of the unit. A conversion stops qualifying as a conversion if it increases height or excavates more than fifty cubic yards. The building permit site plan must be fully dimensioned, showing property lines, direction of drainage, streets, driveways, locations of all structures, easements, and any off-street parking, and a deed restriction is recorded with the County of Marin.

The handout does not name a licensed surveyor, and we will not claim Mill Valley requires one. What we will say is that on these lots, four feet measured from the wrong line is the difference between a building-permit-only ADU and a discretionary application; that on a canyon slope, finished grade at the lowest exterior wall is the entire height calculation; that fifty cubic yards of excavation is a quantity you cannot estimate without existing ground; that the thirty-foot creek top-of-bank setback applies here; and that removing a tree to make room pushes the project into additional review. Inspectors also commonly want a surveyor to verify foundation forms before the pour.

One scanned visit covers it: boundary resolved from monuments and record, existing structures and the proposed footprint dimensioned to the lines, drainage direction and driveways, easements plotted, trees located, contours and finished grade where height and excavation are in play, and top of bank where a creek is near. Deliverables are a stamped, fully dimensioned site plan base map, a layered DWG, and staked corners. See our Mill Valley topographic surveys and ADU survey requirements in the Bay Area.