Nevertheless, net change in households and housing unit authorizations tend to move together. In all Ninth District states housing unit authorizations tended to parallel the change in households during the last three decades. But special factors appear to have caused them to diverge in the early 1990s. In all district states, except Montana, housing unit authorizations exceeded the change in households, as low interest rates and accompanying increase in affordability spurred housing construction. In Montana, which is experiencing substantial in-migration, housing demand appears to be outpacing housing supply.
Demographics also provides some insight into the type of housing units constructed.
The percent of single-family units constructed has been increasing in Minnesota, Montana and South Dakota. Economic factors and tax changes have influenced this increase, but demographics undoubtedly has some role, for as people age they can more likely afford single-family housing. However, the percent of single-family units constructed has been relatively constant in North Dakota and Wisconsin. Also, since the early 1980s in all district states the value of a single-family building permit has increased markedly. This trend in part reflects the movement of the baby boom generation into higher income brackets as they are maturing into their middle years.