Elizabeth Lesly Stevens writes a column for The Bay Citizen.

In San Francisco, one of the toughest places in the country to find a place to live, more than 31,000 housing units — one of every 12 — now sit vacant, according to recently released census data. That’s the highest vacancy rate in the region, and a 70 percent increase from a decade ago.

To know one big reason why, ask Wayne Koniuk. By trade, Mr. Koniuk fashions artificial limbs for amputees. By habit, he fits prostheses at no charge for people who cannot pay. This has left him a less-than-wealthy man.

But he does have one substantial asset: a Divisadero Street building that his father, Walter, an orthotist, bought in 1970 and gave to his only son in 2001 so Wayne could run his business on the ground floor and Wayne’s adult children would always have a place to live.

“For eternity,” Mr. Koniuk recalls his father saying, “my grandkids will always have a place they can go. No matter whatever happens, that building should stay in the family.”