Andrew Girardeau-Dale finished college a few years ago, but when the 24-year-old aerospace engineer shows me his new place in Seattle, Wash., it's like being back in a dorm room. I take notes perched on his desk chair, while he sits a foot away on the end of his bed, displaying the features of the kitchen behind us, which consists of a sink, small fridge and hot plate. "I thought about getting a second one so I could cook rice and stir-fry at the same time," he says, "but now I just cook the vegetables with the rice."

Low-key in demeanor and dress, and with his hands often tucked in sweatshirt pockets, Girardeau-Dale says the aPodment – the developer's name for this type of ultra-compact apartment, otherwise known as microhousing – fits his minimalist personality. And at $775 a month, including utilities, it gives him a chance to both save for the future and live in Capitol Hill, home to artsy trendsetters since the Northwest's legendary grunge era. A typical studio in this centrally located, apartment- and bar-filled neighborhood goes for at least $1,200 a month.

Measuring 150 to 250 square feet, aPodments come with bathrooms, kitchenettes and basic furnishings, but share laundry, common space and a full-sized kitchen, stocked with pots, pans and utensils, with other units. This means that each cluster of tiny studios counts as a single unit under city housing code. The Seattle Department of Planning and Development started receiving building permit applications for aPodments and similar types of microhousing in 2008, during the depths of the recession.

Since then, rents have continued to rise – in July, they were up 5.8 percent over the previous year citywide, and a whopping 8.2 percent in Capitol Hill – even as vacancy rates keep falling. Microhousing has expanded accordingly: As of last November, 29 microhousing projects across the city had received building permits and 15 more were in the permitting process. About 12 of the permitted projects are completed and renting. All boast cheaper rents than the norm, opening rapidly gentrifying urban cores to those with less money to spend or stuff to store. Though some locals worry that the influx of new residents will damage neighborhood character, many cities increasingly see microhousing as a way to deal with the affordable housing crunch. Microhousing can also contribute to Seattle's goal of becoming carbon-neutral by 2050.

For the first time, the majority of the world's people live in cities, and with the urban population set to nearly double by mid-century, cities will necessarily lead the way in reducing global emissions. This requires density: Concentrating people in walkable, mixed-use neighborhoods where they can share the same resources and be as mobile as possible without driving. The challenge is to keep these desirable neighborhoods from becoming prohibitively expensive, forcing folks of lesser means into the suburbs, where they'll spend what they save on rent on gas-guzzling commutes – a trade-off that perpetuates poverty and decreases urban density's carbon benefits.

More people moving into cities is "a healthy thing on so many levels," says San Francisco Supervisor Scott Wiener, "but the downside is much more competition for housing, which just makes things more expensive. It reduces the economic and cultural diversity of the city."

In fall 2012, Wiener sponsored successful legislation to create a microhousing pilot program in San Francisco that would lower the minimum required square footage for an apartment from 290 to 220 square feet, for a test run of up to 375 new units. In New York City, where new apartments in higher-density areas must be at least 400 square feet, former Mayor Michael Bloomberg sponsored a design contest last year for spaces smaller than that, and construction of the winning project is now underway. Denver also held a microhousing design competition in 2013. Microapartments are now popping up in Portland, Ore., and Vancouver, B.C., has begun allowing backyard cottages and mother-in-law units virtually citywide.

Microhousing is not a brand-new concept – really, it's an updated version of the rooming houses and single-room-occupancy hotels that, in the first half of the 20th century, housed a significant share of young and single urban workers. Over the last 50 years, city housing codes and zoning laws systematically outlawed them, mainly for health and safety reasons. But that left many low-income people with few realistic housing options inside urban cores, says Alan Durning, executive director of the Sightline Institute, a Seattle-based sustainability think tank. "If all you can afford is a 100-square-foot room, then a one-bedroom apartment doesn't do you much good."

Microhousing is, essentially, market-provided "non-subsidized affordable housing," says Seattle DPD spokesman Bryan Stevens. Though far from a panacea for affordability and sustainability issues, given its niche market, Durning speculates that it may help free up subsidized housing for the poorest citizens and those with special needs. It might also give low-income families a better chance at the many single-family homes and bigger apartments currently occupied by groups of roommates who can't afford to live alone.

Opponents most commonly worry that the developments will increase pressure on urban neighborhoods' already limited street parking. But given their location in walkable, transit-rich neighborhoods, these dwellings clearly cater to the carless. In the zones where microhousing proliferates in Seattle – mainly Capitol Hill and the University District – the city has no vehicle-parking minimums, but it does require a secure, covered bicycle parking spot for every four units of a multifamily building, and proposed rules would require the same for microhousing sleeping rooms. Seattle DPD also plans to tweak regulations to ensure that aPodments undergo proper design review, giving neighbors more opportunity to voice concerns.

The only downside to his new digs, says Girardeau-Dale, is that it's hard to entertain there. He suggests we decamp to a coffee shop for our interview, but I want to get a sense of what it's like to spend more than a few moments in this space, which he considers an upgrade over the place he shared with three roommates. I can't imagine cramming all my thrift-store sweaters and knick-knacks into this cubbyhole. Then I step to the room's fourth-floor window and gaze out over the tops of neighboring apartment buildings to where a gorgeous winter sunset bleeds across the sky.

The view, as Girardeau-Dale notes, makes the room seem much bigger.

Claire Thompson was an editorial assistant at Grist before a stint with the Southwest Conservation Corps in Colorado. She's now writing and working again in Seattle, her hometown.