AEC definitions
A setback is the minimum distance a building must be kept from a property line, a street, or another feature the zoning ordinance names. The site plan dimensions it. How you measure height, eaves, and steps is defined by the ordinance, not by custom.
Definition
Front, side, and rear setbacks can differ, and they can increase as the building gets taller. A survey locates the property lines the setback is measured from. An easement can prohibit building even inside the setback. Encroaching is a zoning violation. The remedy is a redesign or a variance, not a quieter line weight. Building-code fire separation distance is a different measurement, from the building face to the line, used for wall ratings. Do not use one number for both without checking.
In depth
Some codes measure to the foundation, some to the eave, some to the average of a stepped facade. Write the rule you used next to the dimension.
Corner lots often have two fronts. Assuming the short side is the side yard is a common error.
Property lines on an old site plan are not a boundary. The civil and architectural site plans should use the same survey. A building laid out from an assumed line is an encroachment risk.
Recorded easements are plotted on the same sheet.
Ordinances often allow limited projections into a setback and forbid others. A bay window the architect loves may be the thing the planner rejects. Check the projection section before you fall in love.
Underground parking sometimes has its own setback. Do not assume the surface rule covers the garage.
The building code may require a rated wall when the building is close to a line, even when zoning allowed that distance.
Both can apply. The wall section and the site plan have to agree.
Examples
The site plan dimensions 25 feet from the property line to the face of the building and notes that eaves may project 2 feet under the ordinance.
A corner lot treats both street sides as front setbacks. The plan is revised.
The building meets the zoning setback and still needs a rated wall because the fire separation distance is small.
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