The average finished floor space of basements dropped to 96 square feet in 2015, down a bit from the high of 99 square feet in 2014.
According to NAHB, before the dip, finished basement floor area had been on the rise since 2009, when the average was 65 square feet. A basement’s finished floor space is factored into the house’s total square footage.
Conveniently, this turns out to have little effect on the basic trends. With or without finished basement area, the average size of a new home increased every year from 2009 through 2013, stayed essentially flat in 2014, then increased again to an all-time high in 2015. Similarly, the median size of a new home increased every year from 2009 through 2013, declined slightly in 2014, then increased to an all-time high in 2015—whether or not finished basement area is taken into account.