Building setback lines appear on subdivision or lot plats or by zoning laws as areas that restrict the location of improvements behind or within certain boundaries. The most common building setback line is the minimum building setback line that designates the building setback from a street, right of way or side lot lines. The minimum building setback line (MBSL) is designed to insure conformity in the location of improvements within the development or subdivision. It is not uncommon for improvements to encroach upon minimum building setback lines to a small degree, especially on small, irregularly-shaped lots, corner lots, or lots developed on a cul-de-sac.
Another type of building setback line is the building envelope. The building envelope is a designated buffer zone around the perimeter of an entire subdivision or development in which improvements should not be located. Minor encroachments onto this type of building setback line are more rarely seen than in minimum building setback line situations, but they do occur.