PORTLAND, Ore. -- They're called ADUs or accessory dwelling units. You might know them better as "mother-in-law apartments."

And if you're interested in having one but can't afford it, Portland start-up Dweller will pay to build one for you.

Patrick Quinton co-founded the company about year ago. The former Executive Director of the Portland Development Commission, Quinton new well the need for affordable long-term rental housing in Portland.

He also saw the popularity of ADUs explode in recent years.

"Roughly speaking, I think there are a couple thousand permitted ADUs, but we know there's probably more out there and there's a lot of demand for new ADUs," Quinton said.

But building the small detached homes can get expensive. It typically costs property owners an average of $150,000 per unit.

Homeowners can get a Dweller ADU in their backyard without paying anything up front. They just need to be willing to lease out part of their yard.

"We'll build an ADU on somebody's property, retain ownership, lease it out for them, and share the rent with the homeowner," said Quinton.

That share is 30 percent.

Homeowners have the option of buying out the company at any time or they can purchase a turn-key ADU by themselves right away for $118,000.

Some may wonder how the company is able to get these pre-made homes into backyards in Portland's dense neighborhoods..

The answer? It will use a massive crane which literally lifts the ADU up and over any barriers and places it into the backyard.