For a long time, moving to nursing homes or condo communities for people ages 65 and over were some of the only options for those who are aging. Living in single-family homes – especially if they have more than one level or are too large to clean easily – can be difficult for people as they grow older.

A growing numberof cities are now beginning to think differently about how people can instead age in place, retrofitting neighborhoods to accommodate aging baby boomers.

One approach is the Accessory Dwelling Unit (ADU), which is also sometimes called a “granny flat” or “in-law unit.” The small homes are designed to go in backyards, so that aging parents can have independence and the option to live near their adult children.

A new startup, called Dweller, designs and builds affordable ADUs in Portland, Oregon that can be used for this purpose. Homeowners who live in the city can buy a turnkey home for $125,000, or they can rent one for about $1,200 to $1,500 per month.

Take a look below.

Featuring one bedroom and one bathroom, the 448-square-foot homes are designed for backyards.

Foto: sourceDweller

In the next six months, the startup will offer an even smaller, less expensive model.

The homes cost $125,000 to buy, or up to $1,500 to rent, Patrick Quinton, Dweller's CEO, told Business Insider.

Foto: sourceDweller

Quinton is also the former executive director of the Portland Development Commission.

For rental units, Dweller buys and installs the homes in backyards, and property managers rent out the units to tenants. The startup then splits the revenues 70-30 with land owners.

Foto: sourceDweller

The rental price can vary by city, which may also have their own regulations regarding the construction of ADUs.

Owners can choose the home's cabinets, countertops, flooring, and paint colors, as well as if they want a washer/dryer and a shower or tub.

Foto: sourceDweller

The whole process around 4 months, from signing an agreement to handing over the keys. But the actual unit takes less than 30 days to build in an off-site warehouse.

Foto: sourceDweller

Once completed, the home is installed on-site via crane.

Foto: sourceDweller

Dweller is only working in the Portland metro area right now, but plans to expand to other American cities within the next year.

Foto: sourceDweller

Like many American cities, Portland is in the midst of an affordable housing crisis. The metro's medium home price is $469,000, and the majority of its existing housing supply consists of single-family homes.

Foto: Homes in a Clackamas County neighborhood outside Portland, Oregon.sourceJPL Designs/Shutterstock

Sources: Oregon Metro, Zillow, and The Oregonian

That means older residents who want to downsize may not have too many affordable options. Dweller's homes are a part of the "aging in place" movement, which aims to help people stay in their communities as they grow older.

Foto: An elderly couple looks out at the ocean as they sit on a park bench in La Jolla, California November 13, 2013.sourceReuters

Cities like New York and Philadelphia have local organizations and officials that are working to retrofit their neighborhoods for aging populations. This can consist of everything from advocating for accessible home construction to building more sidewalks for those who can no longer drive safely.

"Our units offer families the opportunity to add living space nearby and provide care or supervision if necessary," Quinton said. "In this way, they may allow aging parents to live closer to their children for a longer period of time."

Foto: sourceDweller

While it's common for aging parents to live in Dweller's ADUs, Quintin said that he's also seen a lot of interest from young people.

Foto: sourceDweller

"Portland has a severe shortage of housing - especially rental housing for low- and moderate-income renters," Quinton said. But the city also has "an extensive inventory of single-family properties with backyards ... and plenty of room to add housing."