Help me understand why so many huge self-storage complexes have cropped up around Southeast Portland. Are they being leased? Is there that big of a demand for them? It is freaking me out. —So Much Storage

I suspect by the time you read this, the only thing Portlanders will want to know about self-storage units is whether you can barricade yourself inside one to survive the plague-driven apocalypse. Still, I can at least offer the comfort that you're not hallucinating—Portland really is the nation's fastest-growing market in the already-fast-growing self-storage sector.

Like the rest of the U.S. economy, the self-storage industry is built on the faith that Americans will never stop trying to fill the gnawing void at the core of their being with bulky consumer goods. This has so far proven to be a good bet.

In Portland, there's the added pressure of 30,000 new residents per year, as well as a long-term trend away from single-family homes (with their ample basements and garages) in favor of density-friendly apartments.

Providing room for America to store the Styrofoam packing blocks from appliances we no longer own (and other stuff) is a $38 billion business—roughly the same size as the entire worldwide smartphone-app sector—and the volume of space currently commanded by this industry is equivalent to about 430 Empire State Buildings.

For developers, this is easy money. It's true that self-storage units (in Portland) don't net quite as much rental cash per square foot as apartments ($1.25 vs. $2 per month). However, it's also true that being landlord to a couple pallets of '90s-era CRT computer monitors is a lot less hassle than having human tenants, who tend to want fussy things like air conditioning and running water and hidden-camera-free bathrooms.

Recently, however, we've been adding units so rapidly—annual increases have topped 20 percent—that some industry insiders worry we may be approaching "peak storage" (which, coincidentally, is the nation's least-interesting environmental crisis).

Most observers still continue to be bullish on the industry's long-term prospects, but local prices have come down a bit—if you're looking to become one of the 30 million Americans who pay $100 a month to postpone a trip to the dump, this could be your moment.