Expedia historically has been very slow to do things. It took forever to get involved in social media and, fearful of angering its big hotel partners, it took until this month for Expedia to announce it would begin offering vacation rentals from HomeAway.

When you are a big, bad online travel agency such as Expedia, you can seemingly bide your time, see how markets shake out, and acquire up-and-coming companies.

No need to rush things.

But recent research from PhoCusWright, U.S. Vacation Rentals 2009 – 2014: A Market Reinvented, shows why Expedia is finally getting into vacation rentals in a much more meaningful way than it ever has.

One of the key findings is that U.S. travelers spent $23 billion on vacation rentals in 2012 — and that amounted to nearly one-fifth of the U.S. lodging market.

That $23 billion number is actually lower than pre-recessionary levels, but what is changing is that the percentage of vacation rentals that are transactable online have doubled from 12 percent in 2007 to 24 percent in 2012, PhoCusWright says.

And, when vacation rentals are bookable online, then that's in Expedia's sweet spot.

"While rentals through property management companies have been in OTAs for years, this [the Expedia-HomeAway deal] opens the door to the full universe of inventory," says PhoCusWright's Douglas Quinby, one of the report's authors. "It put what was the square peg of rental inventory into the round hole of the online travel distribution system, which was largely built around hotels."

"And, it helps Expedia's competitive footing with Booking.com, which has been making inroads into this market through direct relationships with property management companies," Quinby says.

Expedia's pilot program to offer vacation rentals from HomeAway is slated to kick off in 2014, although neither party has offered much detail on how it will work.

Here's an infographic on key findings from the PhoCusWright vacation rental study:

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