NEW YORK (CNN/Money) - New home purchasers own a lot less of their homes than ever before, according to a study released Tuesday by SMR Research, which studies market trends in the mortgage industry.

In the first six months of 2005, 38.1 percent of home buyers who financed their homes did so with a down payment of five percent or less of the purchase price, up from 30.6 percent in 2000.

And the percentage of buyers paying the traditional 20-percent downpayment fell to 33.7 percent of borrowers, down from 39.1 percent in 2000.

Usually, lenders require that buyers putting down less than 20 percent purchase private mortgage insurance (PMI), which adds a couple of percentage points to their interest rates.

SMR points out, however, that relatively few of these buyers actually wind up paying for PMI.

Instead, these buyers use "piggyback" mortgages. Piggybacks consist of two loans, a regular mortgage, which covers the first 80 percent of the home cost, and a home equity loan or home equity line of credit, which pays for the rest.

SMR reports that piggybacks now account for 48.2 percent of all home purchase mortgage dollars, a stunning rise from 19.9 percent in 2001.

The use of so much leverage makes real estate markets increasingly risky, because lack of home equity gives people one less asset to fall back on in times of need.

Increasing home prices have reduced some of this risk but other factors, such as more single home buyers, more borrowers with blemished credit records, and a proliferation of interest-only and other non-traditional mortgages have added to it.

If housing prices flatten out or decline, some newer homeowners who have built up little equity, could find themselves "upside down" -- owing more than their houses are worth.

And, if interest rates rise, homeowners with adjustable rate mortgages may not be able to keep up higher payments or sell the house for what they paid. Foreclosures could spike and the supply of homes for sale soar. That could send the real estate market into a tumble.

Homeowners are also cashing out home equity like never before. For more, click here.

Some homeowners are in danger of owing more on their mortgage than their home is worth. Click here for that story.