From time to time, Dee Williams does a possession count. The last tally was 305.

In many homes, that may amount to the stuff found in the kitchen cupboards, or the contents of one walk-in closet. For Ms. Williams, it included all of her worldly belongings, from her bedroom suite (a mattress and a quilt) to her home entertainment equipment (a laptop) to her jewelry collection (four pieces in all: two necklaces and two pairs of earrings).

“That’s everything,” she said, adding that she recently ordered a book on house design, a big splurge. “I’m constantly going through my stuff, figuring out what I should get rid of. Creep happens.”

When your house is 84 square feet, life gets pared down.

Ten years ago, Ms. Williams, now 51, sold her three-bedroom bungalow in Portland, Ore., built a tiny house on a metal truck trailer and drove it to Olympia, Wash., where it came to rest in the backyard of her friends Hugh O’Neill and Annie McManus. Her “great room” is too small for a couch, her upstairs is just a sleeping loft with a skylight. There’s a kitchen counter with a propane one-burner, but no oven or refrigerator. There are lights, but they run on solar power. There’s a sink and a toilet, but no running water (which means composting and no shower).

Visitors to the property may be forgiven for thinking someone had taken up residence in a beautifully built pine-and-cedar toolshed out back.