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New, privately-owned residential buildings currently authorized by a building permit or started in areas not requiring a building permit.
This is on the "About the surveys tab" on the census page - https://www.census.gov/construction/nrc/about_the_surveys/soc.html. Understanding how one collects detail on housing starts in areas that don't require a building permit is done, or how to calculate sampling errors related to that, is fairly arcane, and likely not impactful with respect to what we are doing in FIBO with economic indicators.
Coverage = Population for housing starts (see above).