The day will be a historic one. A referendum will result in a decision as to whether the United Kingdom Remains or Leaves the European Union, carrying with this fateful resolution countless global economic collateral effects.

Here, in San Francisco, at the Pacific Coast Builders Conference, Brexit looms as another in a series of "headline risk" events that stir up uncertainty, mess with consumer or investor sentiment, and pose potentially material impacts on interest rate policy in the United States and in other, weaker world arenas.

But Brexit is far off and abstract. San Josexit, Bay Arexit, Los Angelexit, San Diexit, are close to home and very real, at least among the home building, development and design community attendees at PCBC this year.

Attainability--which would put homeownership within the means of normal wage-earning households--has become a fraught issue among residential developers and builders. They're talking more and more about sons and daughters of theirs and their friends' who've begun evacuating the area because they can't make the cost of housing pencil with their household pay and projected earnings.

"My son is a doctor, and he couldn't afford to live here," one senior-level residential architect told me. "He came out of med school with $150,000 in debt, and he and his wife are both highly skilled, but he had to move to Arizona. Now, he's making twice as much money as he would have in the Bay Area, and the cost to own a home is half or less what it costs here. And you know what? We Baby Boomers are baby chasers, so you can be damn sure that his mother and I will be retiring to Arizona to be closer to them."

This is one anecdote, an example this fellow cites to say that Northern and Southern California cities are at risk of losing critical resources--Millennial and Baby Boom residents--as prohibitive zoning, high land development costs, regulatory fees and expenses, and time delays make attainability a figment of wishful thinking in the real world.

But anecdotes and corridor talk at PCBC are not all.

This morning, Redfin looks at its "Digital Diaspora" data, clocking in on behavioral statistics that show people in hot tech hubs looking to move to other markets for better balance between their means and what's available in housing. Redfin data scientist Taylor Marr writes:

Last year, we discovered that about one in four people who were searching on Redfin from the San Francisco Bay Area were looking for homes in other parts of the country. That was up from about one in seven in 2011, having increased consistently over the four years. As of this spring, the portion of Bay Area buyers looking to move has leveled off, but what’s changed is where they’re looking to go. Most notably, Seattle has become a less popular destination, while “other” cities, which include Washington, D.C., Austin, Denver, and Boston at the top of the list, have become more common havens for those fleeing the Bay Area.

Here, RealtyTrac, notes that more places--namely, the same places Redfin has mapped as ones undergoing an exodus--are unaffordable by historical measures than were a year ago. It's still less than one in five metro areas, but one can see from the RealtyTrac affordability heat-map the geographical clusters that may someday need to content with hemorrhaging populations of both younger adults and their retiring Baby Boom parents.

Counties least affordable by the absolute standard of percentage of wages needed to buy a median priced home were Kings County (Brooklyn), New York (121.7 percent of average weekly wages to buy a median-priced home); Marin County, California in the San Francisco metro area (118.1 percent); Santa Cruz County, California in the Santa Cruz metro area (113.5 percent); San Francisco County, California (94.6 percent); and Maui County, Hawaii (92.8 percent).

Other counties among the top 25 least affordable by historic standards included counties in Los Angeles, Honolulu, Sacramento, San Diego, and San Jose.

Withdrawing from those markets--one household at a time--will come with a price. That hits pretty close to home. Do you know the way from San Jose?