Pardon me for over-simplification:
Assuming 3.2 people stay in 1 house, for 320 million population, it would require 100 million houses. Let us assume 80% occupancy (20% extra houses that are empty). It means 100*100/80 =125 million are the number of houses that the country needs.
Housing starts are at over 1 million per month -
Let us say 1*12=12 million new houses per year are being made in USA.
So that means the system assumes life span of a house is just abt (125/12=) 10 years.