Source: U.S. Bureau of the Census, Construction--Building Permits. Updated monthly, summarized here annually. http://www.census.gov/const/www/permitsindex.html.
Building permits represent the number of new privately-owned housing units authorized by building permits in the United States. A housing unit, as defined for purposes of this report, is a house, an apartment, a group of rooms or a single room intended for occupancy as separate living quarters. Separate living quarters are those in which the occupants live separately from any other individuals in the building and which have a direct access from the outside of the building or through a common hall. In accordance with this definition, each apartment unit in an apartment building is counted as one housing unit. Housing units, as distinguished from “HUD-code” manufactured (mobile) homes, include conventional “site-built” units, prefabricated, panelized, componentized, sectional, and modular units. Housing unit statistics in these tables exclude group quarters (such as dormitories and rooming houses), transient accommodations (such as transient hotels, motels, and tourist courts), "HUD-code" manufactured (mobile) homes, moved or relocated units, and housing units created in an existing residential or nonresidential structure.
These numbers provide a general indication of the amount of new housing stock that may have been added to the housing inventory. Since not all permits become actual housing starts and starts lag the permit stage of construction, these numbers do not represent total new construction, but should provide a general indicator on construction activity and the local real estate market.
The value of new private housing units is the sum of the estimated valuation of construction on each building permit authorized in that year by local permit-issuing jurisdictions.
Scope and Methodology:
Building permits data are based on reports submitted by local building permit officials in response to a Census Bureau mail survey of 20,000 permit-issuing places. They are obtained using Form C-404, Report of New Privately Owned Residential Building or Zoning Permits Issued. Data are collected from individual permit offices, most of which are municipalities; the remainder are counties, townships, or New England and Middle Atlantic-type towns. When a report is not received, missing data are either (1) obtained from the Survey of Construction, which is used to collect information on housing starts, or (2) imputed.
The number of new housing units authorized by county is obtained by directly cumulating the data for the permit-issuing places to counties. Although not subject to sampling variability, data are subject to various nonsampling errors. Explicit measures of their effects generally are not available, but it is believed that most of the significant response and operational errors were detected and corrected in the course of the Census Bureau''s review of the data for reasonableness and consistency.
The portion of residential construction measurable from building permits records is inherently limited since such records obviously do not reflect construction activity outside of areas subject to local permits requirements. For the nation as a whole, less than 2 percent of all privately owned housing units are constructed in areas not requiring building permits. However, this proportion varies greatly from state to state and among counties. Any attempt to use these figures for inter-area comparisons of construction volume must, at best, be made cautiously and with broad reservations.