Some affluent buyers are getting the keys to their new home without putting a penny down.

It’s 100% financing—the same strategy that pushed many homeowners into foreclosure during the housing bust. Banks say these loans are safer: They’re almost exclusively being offered to clients with sizable assets, and they often require two forms of collateral—the house and a portion of the client’s investment portfolio in lieu of a traditional cash down payment.

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In most cases, borrowers end up with one loan and one monthly payment. Depending on the lender and the borrower, roughly 60% to 80% of the loan can be pegged to the home’s value while the remaining 20% to 40% can be secured by investments. On a $2 million primary residence, for instance, the borrower could get a $2 million loan, which would require a pledge of assets in an investment portfolio to cover what could have been, say, a $500,000 down payment. The pledged assets can remain fully invested, earning returns as normal, without disrupting the client’s investment goals.

While these affluent clients may be flush with cash, this strategy allows them to get into a home without tying up funds or making withdrawals from interest-earning accounts. And given the market’s gains combined with low borrowing rates in recent years, some banks say clients are pursuing 100% financing as an arbitrage play—where the return on their investments is bigger than the rate they pay on the loan, which can be as low as 2.5%. Some institutions offer only adjustable rates with these loans, which could become more expensive if rates rise. In most cases, the investment account must be held by the same institution that’s providing the loan. See: Home improvement gets a makeover

These loans also provide tax benefits. Since borrowers don’t have to liquidate their investment portfolios to get financing, they can avoid the capital-gains tax. And in some cases, they can still tap into the mortgage-interest deduction. (Borrowers can usually deduct interest payments on up to $1 million of mortgage debt.)

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While these loans make up a small portion of banks’ overall lending, demand for them has been rising. BNY Mellon Wealth Management’s mortgage team says it experienced a 10% increase in requests for 100% jumbo-mortgage financing involving clients’ investment portfolios in 2012 compared with a year prior. BOK Financial, which offers up to 100% financing just to medical doctors through its private-banking divisions in eight states, including Arizona, Oklahoma and Texas, says there has been a roughly 25% increase (or about 100 more borrowers) in this lending from a year ago. Also, at Citi Private Bank, applications have been growing over the past two years. “Demand is two to three times what it normally is,” says Peter Ferrara, managing director of the private bank’s residential real estate.

Some banks are using this product to lure in clients, such as BOK Financial’s offer, which is available to new physicians. To provide the loan, the bank must first receive proof that the borrower has cash or investments, like stocks or mutual funds, that equal 10% of the borrowed amount. (The company says it doesn’t seek a pledge of those assets but just wants to know that borrowers can meet their obligations over time.)

What to consider before signing up: