Municipal zoning regulations are in a constant state of flux - especially when considered in relation to the long life span of many Massachusetts' residential and commercial structures. As such, many homes and commercial properties do not conform to current zoning regulations, particularly concerning issues like frontage, side and rear yard setbacks, and floor-to-area ratio (square footage of a structure in relation to the total area of the lot). Often, these structures were built in conformance with the applicable zoning regulations, but have subsequently fallen out of compliance due to increasingly strict requirements. These structures are thus categorized as "pre-existing nonconforming", and are protected from the more restrictive zoning requirements as long as the structures remain unchanged.
Considering the age of many single and two-family homes within the Commonwealth, and the relative time period when zoning ordinances and by-laws came into effect across municipalities, it is common to find that many homes often do not comply with current local zoning requirements.