Whether the house is constructed properly or not, is somewhat irrelevent.
Mortgage this property, with no down payment, to someone who's loan application clearly shows they can't possibly pay, collect your broker's commission... bundle that transaction with a couple million more of the same ( oh yes, at a commission )... call it real estate secured investments... sell it to larger and larger institutions, whose real estate secured stocks and bonds me and you are buying hoping to retire someday, and you have what we got today.
Oughta be a lotta people in jail... Mainly the ones who watched it happen and neglected to make such crap illegal. So long as the prices kept rising and the places could be "flipped" ( with the accompanying TV show ) at a profit, everybody involved was happy with their little house of cards. Never mind the po' folks and their families who got tossed outta their houses.
Not to worry though... Congress'll make sure the rich guys running the scheme'll get out OK .