Buying a full duplex and becoming a homeowner and landlord at the same time can be a good financial investment, but real estate experts said these properties are not so easy to find in the Washington metro area.

"In Northern Virginia most of the duplexes or town homes are considered as 'attached homes,' meaning you can only buy one half," said Casey Margenau, associate broker with Re/Max in McLean. "Most people don't buy both sides."

That doesn't mean it's impossible to find a full duplex for sale, although you could have to purchase from two owners.

"The advantage of buying a duplex is the added income generated by the other unit," said Brandon Green, president of Brandon Green Cos. in the District. "Essentially, a duplex is an investment property and over time adds to a portfolio of real estate which can build wealth."

To make sure buying a complete duplex is a good decision, Margenau said to run the numbers. "Look at the return you would get if you paid cash," he said.

Aim for an 8 percent to 10 percent return on investment. For example, a buyer who purchased a duplex for $200,000 to live on one side and rent out the other would want to generate just over $1,300 a month in income, after taxes and insurance, to make a profit. That would mean renting one side for $1,600 to $1,800 a month.

"That's reasonable in today's marketplace," Margenau said, "and it allows you to let your tenant pay off the mortgage."

Getting that mortgage, however, can be a challenge.

"Some lenders view duplexes as investment properties," Green said, "and therefore, will require at least 20 percent down and a higher interest rate." Margenau said some banks break the purchase of an entire duplex into two loans.

There is a bright side, however, some lenders may be more likely to qualify borrowers for a loan if they will be living in the duplex they buy.

"You're less likely to default from the bank's standpoint if you're living in the home," Margenau added.

Buying a duplex with tenants already in place is not necessarily problematic as long as they pay their rent on time and maintain the property. Margenau said it is a good idea to make sure would-be tenants have a good rental history before deciding on a deal.

Having a duplex already rented could make it easier to determine a return on investment and make the bank happy, too. But there is one downside.

"If you happen to get a tenant you don't really like, living on the other side of the duplex can be problematic," Green said.