I'm not saying it is a valid presumption (in fact, I know it really isn't), but the presumption when it comes to living on SS income is that you don't pay rent; the presumption is that you own your home free & clear by that point in your life. We cleared our mortgage so long ago that I don't even remember offhand when it was, but I know it was before my youngest child was born. Of course, that means that we are trapped where we are; we cannot afford to take on a mortgage when we have college costs yet to bear. (And yes, we saved enough to pay tuition as long as they choose relatively lower-cost schools, but it is still roughly equivalent to supporting two households.)
Our house is tiny and very outdated by today's standards. I do wish it were a *bit* larger, but wishes ain't horses, so it isn't. We really don't want to spend money trying to enlarge it, because if we did, it would run too close to the property lines for comfort, anyway.
I always tell people my retirement plan is dying young, LOL.