While we were busy blaming empty condos for the affordability crisis, we might have overlooked a less obvious culprit.

A Simon Fraser University master's student released her findings this week that show short-term rentals on Airbnb may be contributing to the city's near-zero vacancy rate.

Airbnb is the hugely popular site where people the world over can make money by providing accommodation in their homes, or helping people find affordable places to stay while travelling. The accommodation can be as basic as someone's couch or as opulent as someone's yacht or penthouse. The sky is the limit. As part of her thesis, Karen Sawatzky obtained the data from Airbnb's website, crunched the numbers and discovered that 71 per cent of Vancouver Airbnb listings are for entire homes. It's a significant finding, because it means that if the majority of Vancouver Airbnb hosts have entire apartments or houses to spare, then they're not renting them out to full-time tenants. A significant chunk of the rental stock is lost.

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It means Airbnb's popularity could be contributing to the critically low vacancy rate, which is, in turn, driving up rents.

Since January, city of Vancouver Airbnb listings have increased 17 per cent, bringing the number to 3,473 listed properties. The majority of listings were downtown. More interesting, however, is the finding that 381 of the hosts control 1,215 of the listings for entire homes. It would make sense that the majority of those rentals are investment properties.

"I thought 71 per cent was quite high, and worth poking into," Ms. Sawatzky said, in an interview. "And the number of hosts with more than one listing is high, too. They are really concentrated close to the core, where residents also want to live. To me, that really raises policy issues."

She's right: 71 per cent is high. Only 57 per cent of New York hosts rent out their entire homes, and in San Francisco, it's 60 per cent, according to her research.

Her numbers shed some light on the old question of empty condos. Perhaps it's not so important when investor condos go dark. Maybe the bigger issue, in terms of general affordability, is when they are turned into businesses.

Adjunct UBC planning professor Andy Yan released findings a few years ago that 50 to 60 per cent of all downtown condos are owned by investors who'd purchased them as secondary properties. The much-publicized concern at the time was the 5 or 8 per cent that were left empty. The assumption was that all the other non-owner occupied properties were being rented to residents.

But why would anybody keep an empty condo when they can make double the average rent by renting it short term?

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Considering that the resale value of the average condo has flat-lined for the past several years, the condo investor would do better with a shorter-term rental instead of selling or leasing to a full-time tenant.

Airbnb, which offers rooms and properties for stays as short as on night, is only a part of the shorter-term rental market. While that online company is often criticized for shirking responsibility when problems arise, there are more secure ways for condo owners to manage a shorter-term rental. In fact, several local companies and a lot of condo owners are thriving in that bustling below-the-radar market. Condos are being purchased for the express purpose of short-term rentals. Rents are already high in Vancouver, but a short-term rental can command even more money. And with resale prices so tepid, why break even when you can generate a lucrative revenue stream?

Developer Will Lin sold 12 units at the Rolston condo tower downtown to one investor who bought them for rentals that are longer than a hotel stay and shorter than a regular tenant stay. Let's call it a long hotel stay.

"It's like a hotel service but with a longer stay – longer stay meaning a month," Mr. Lin says.

Heather Wood is property manager for Rent It Furnished Realty, the company that manages the units at the Rolston.

They manage about 1,500 condo units that are owned by many individuals, she says, and the majority of them are rented for stays between three and six months long. Vancouver is such a hot destination that all units are sold out.

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"The focus is mostly in downtown Vancouver," Ms. Wood says. "But there's been such a demand from owner clients to list their properties with us that we have a presence on the North Shore and a little bit in Burnaby and Coquitlam. We have spread our geographical boundary a little bit, but mostly they are downtown core."

Ms. Woods's company does not do Airbnb rentals. The company is licensed to do a minimum of one-month stays. Their units run from mid-range to high end, with several at the Shangri-La. The owners furnish the units, including linens, dishes and towels. It's a turnkey operation.

"Most are for stays of between three to six months and we handle mostly professionals. Vancouver has gone a little nuts this summer, so we're inundated with short-term rental requests right now. We don't have any inventory – it's all sold out."

Many condo buildings are creating new strata bylaws that require a minimum stay of three months, she says.

"The stratas that govern the buildings are really clamping down on Airbnb. The residents don't want it to be like a hotel."

Some of her investors are offshore, but the majority are locals, she says.

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The monthly rent for a one-bedroom is $2,000 to $2,500 and a two-bedroom is $2,800 to $4,000, on average. But luxury suites go for a lot more.

"It ranges from a cute little one-bedroom with nice furniture to a super luxury penthouse."

Some of the people who use their service are locals who live in the suites and rent when they go away. But those are the minority, she says.

"Most of the suites are investment properties, or people who have moved on to something else, but they decided to keep it as an investment."

Mr. Yan, the author of the empty condo report for BTA Works, was intrigued by the potential impact of the few-months-at-a-time renter. That sort of condo use would not have made it into his empty condo study, which was based on electricity usage. He said the short-term renter would have just as big an impact as the empty condo, however, because they are competing with rental stock for the working local looking for a home.

"Remember, there are about 100,000 condo units in downtown Vancouver. What is the percentage of condos for Vancouverites, hypothetically? This is a key question for me."

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He also doesn't blame condo owners looking to tap this little gold mine. "Given what happened to the stock market in '08 or '09, if I'm sitting on $100,000 and I put it into a condo and it gives me a stream of income of $3,000 to $4,000 a month, that's a heck of a return if that income can be consistent. Why not go after short-term rental?"

It begs another question. Homes, whether purchased or rented, are now established winning commodities. Ms. Sawatzky had a vested interest in conducting her research: She's a long-time renter. The gap between renter and owner is growing increasingly wide, and shorter-term rentals aren't helping, she argues. She has appealed to the city to take steps to address the impact of short-term rentals. Councillor Geoff Meggs acknowledged the potential impact on his blog.

Ms. Sawatzky suggests an in-depth look at short-term rentals on specific neighbourhoods, where vacancy rates are lowest.

"Vancouver was in a housing crisis before 2008, and there was already a wealth gap between renters and owners," she says. "But Airbnb is exacerbating the housing inequality that was already unfair."

Mr. Yan says the discovery of this hidden short-term market poses another question in the affordability debate.

"It's fundamentally asking, 'What's the point of housing? Is it a business or a fundamental human need? And how does public policy span the two?' "