New mortgage incentives 'a little risky': Shiller

Lax lending standards were widely faulted for triggering the 2008 financial crisis. If recent developments are any indication, those conditions may be making a comeback.

In an effort to accelerate lending to lower- and middle-income borrowers, mortgage giants Fannie Mae and Freddie Mac are launching programs that will guarantee loans with down payments of as little as 3 percent.

But could an ultralow down payment create a housing market boom, or could it lead to another mortgage bubble? A prominent housing market expert who made his name predicting the 2008 bust has at least some doubts.

"It sounds a little risky," Nobel Prize-winning economist Robert Shiller told CNBC. "Risky for the lender, and for the mortgage insurer who is going to insure" the mortgage obligations, he added.

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Borrowing criteria tightened after the housing market crashed, but in recent days some of those strictures have been loosened. Lack of a big cash down payment has been cited by some as keeping many possible buyers from becoming homeowners.

According to Fannie Mae and Freddie Mac , to get a mortgage with just 3 percent down, borrowers must have a credit score of at least 620. They must also be able to able to prove income, assets and job status, and purchase private mortgage insurance.

However, Shiller still cast doubt on whether that would be the best course of action. "Because it's only a 3 percent margin, if somebody defaults and they have to sell the house, they might not get all the money back."

Fannie and Freddie don't make loans, but they buy and package about half of all new home loans from lenders. Although banks have implemented tighter lending standards, a spate of new borrowing programs have been aimed at first-time and lower-income homebuyers, most of whom have stayed on the sidelines of the housing market.

According to recent data from the National Association of Realtors, first-time homebuyers account for just 33 percent of all home purchases. That's the lowest level in 27 years.

"Maybe there's a cultural change. Our millennials spend more time on Facebook than standing over the backyard fence and talking to the neighbor," Shiller said, attempting to explain the drop in new homebuyers.

"Maybe neighborhoods are not as important. Or maybe there's an urbanization trend going on."

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Another trend that may be spilling over into homeownership is falling oil prices. Crude oil is trading at the lowest prices in more than five years, and Shiller sees a direct impact on the housing market, especially savings in commuting costs.

"I've been worrying about home prices in remote suburbs where they seem to be weaker," he said. "When people see oil prices, gas prices going down, they'll feel more favorable to buying a remote house that's a 45 minute or an hour drive from the city."

With interest rates at historic lows, is now a good time to buy a house, and is it still a good long-term investment?

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"In a sense, it's a good investment because it's only one a lot of people make. So somehow they're motivated to do it.

However, there's a caveat. "Historically, houses have not done well as investments. They haven't really gone up much in value in the last 100 years. And on top of that, they're a nuisance," he said. "You have to take care of them."