In the graph: "Housing Units in the United States", one should point out that number of "Housing Units" is an upper bound on number of "Households". A gap betw

In the graph: "Housing Units in the United States", one should point out that number of "Housing Units" is an upper bound on number of "Households". A gap between "Housing Units" and "Households" indicates some slack. When these two curves coincides, everyone is buying at the margin.