Setback

A setback is the minimum distance zoning requires between a structure and a property line. They are specified separately for front, rear, and side lines, and they differ by zoning district.

How they are measured

Usually from the property line to the nearest point of the structure, but the details vary and matter:

• Some jurisdictions measure to the foundation, others to the roof overhang or the furthest projection
• Corner lots often have two front setbacks rather than a front and a side
• Structures on the property line, like fences, have their own separate rules
• Below-grade and at-grade elements are sometimes exempt, sometimes not

Encroachments

Zoning codes usually allow specified elements to project into a setback: eaves by a limited distance, chimneys, bay windows, uncovered steps. The list is specific and local, and an element not on the list is not allowed to encroach.

Why the survey matters here

Setbacks are measured from the legal property line, not from a fence, a hedge, or a parcel outline in the assessor's GIS. Those approximations are commonly off by several feet, which is more than the margin most designs have. A setback verified against a sealed boundary survey is the only one worth designing to.

Nonconforming structures

Buildings that predate current zoning are frequently closer to a line than today's rules allow. They are usually permitted to remain as legal nonconforming structures, but that status normally does not let you extend the nonconformity. An addition following an existing wall line that already sits inside the setback is a familiar and unwelcome discovery.