The year the original construction of the building was Completed (not the date of any of any later remodeling, addition, or conversion). This item was ascertained for occupied and vacant housing units. For housing units under construction which met the housing unit definition, i.e., all exterior windows, doors, and final usable floors in place, the category "1979 or March 1980" is used. For mobile homes, trailers, and houseboats, the manufacturer's model year is assumed to be the year built. For railroad cars, tents, caves, etc., the date "1939 or earlier" is used. The figures show the number of units in structures built during the specified periods and still in existence at the time of the census. This item was asked on a sample basis.
Year-built data are particularly susceptible to response errors and nonreporting since respondents must rely on their memory or estimates of persons, who have lived in the neighborhood a long time, etc. A 1970 census evaluation study found greater inconsistencies between the census and reinterviews among earlier year-built categories than among categories for more recent periods.
Similar data have been collected since 1940. The categories in 1970 were: 1939 or earlier, 1940 to 1949, 1950 to 1959, 1960 to 1964, 1965 to 1968, and 1969 to 1970.