Cash is playing a more significant role in residential real estate sales right now than at any time in recent memory.

Consider the following:

• The median down payment on houses was 22% last year.

That’s according to a study by Zillow.com of sales involving conventional mortgages in nine major U.S. cities. It’s the highest figure ever since the data started being kept back in 1997.

By comparison, just three years ago the figure was 11%. And back in late 2006, it was only 4%.

The main reason for the change: Banks are tightening their standards and demanding larger down payments to qualify for mortgages. Banks are figuring that borrowers who can afford a larger down payment are less likely to default, and less likely to end up in a situation where they are “underwater” – meaning the value of their house falls to the point where they owe more than the house is worth.

Many people who don’t have a large enough down payment to qualify for a conventional bank mortgage have been looking into alternative mortgages, such as those backed by the Federal Housing Administration or the U.S. Department of Agriculture.

• 28% of home sales last year were all-cash transactions.

That figure comes from the National Association of Realtors. When the organization first began tracking all-cash sales, back in late 2008, the figure was only 14%.

In some markets, the percentage is much higher. In the Miami-Fort Lauderdale area, more than half of all home sales last year were all-cash deals, according to Zillow.com. In Phoenix, the figure was 42%.

Those are extremely high numbers. They suggest that a growing proportion of homes are being purchased not by families but by investors and speculators who believe the housing market has hit bottom and is poised for a rebound.

The numbers also reflect the fact that banks have tightened their lending standards: The proportion of all-cash deals is higher because the number of people who can qualify for a typical mortgage is lower.

Buyers who can make an all-cash offer are often able to negotiate a lower price. Sellers usually prefer an all-cash offer to one with a mortgage contingency, because with a contingency, the deal could fall through if the buyer loses a job or if the bank simply changes its mind.

• New federal rules could mean higher costs for mortgages with low down payments.

One of the causes of the 2008 financial collapse was that many lenders made questionable loans and then packaged those loans and sold them off to others. In response, Congress passed a law last year that requires banks that sell their loans to keep at least 5% of the risk of default. The idea was that banks would be less likely to make bad loans if they had some “skin in the game” and could lose money if the borrowers defaulted.

However, there’s an exception to the 5% rule if a loan meets certain standards. So in the future, banks will have a big incentive to encourage loans that meet those standards.

Congress didn’t specify those standards; instead, it ordered officials from various agencies to come up with them. The officials recently released a preliminary version of the standards. They include:

• Borrowers must put up at least a 20% down payment.
• Only standard 30-year mortgages qualify. No interest-only loans or balloon-payment loans.
• The borrower must live in the home.
• Borrowers must never have defaulted on a loan or filed bankruptcy, and cannot have missed two consecutive payments on a consumer debt in the last two years.
• Mortgage payments can be no more than 28% of a borrower’s income, and total debt can’t exceed 36% of income.

In addition, refinances would require the borrower to have 25% equity in the home, and “cash-out” refinances would require 30% equity in the home.

These standards are quite strict: Only about 20% of the mortgages backed by Fannie Mae and Freddie Mac from 1997 to 2009 would have met them, the government says.

Once the standards are finalized, banks will likely reward borrowers who meet them with lower rates, and “punish” other borrowers with higher rates – making it even harder for them to get a mortgage.

We’ll see what happens. Politics makes strange bedfellows, and an unusual coalition of banks, real estate agents and consumer advocates are all lobbying to change the standards so that more people can afford a home.