Though it's not the usual order of things, some unattached couples say "I do" on a mortgage before saying it at the altar.

The number of unmarried buyers in the U.S. has risen to 8 percent in 2003 from 5 in 1993, the National Association of Realtors reports. The category includes groups of at least two buyers who may be significant others, friends or relatives. For the first half of 2004, such buyers accounted for 9 percent of all U.S. residential property purchases.

But buying property together can bring problems into a relationship, and such couples don't always live happily ever after, say therapists and singles themselves. Romantic couples may not want to deal with documenting how the property will be shared, figuring that once they're married it won't matter. They may not know how state title laws govern ownership of the property or their legal obligations. If they break up, the fact that they've never discussed these matters can complicate the sale of the home or a share in it. Unlike friends who buy property together, a romantic pair may not build an "exit strategy" at the time of purchase.

Couples whose relationships falter after making joint purchases may underestimate the costs associated with homeownership. They may think owning a home is like living together in an apartment and are surprised when confronted by unexpected repair or other problems that require large payments or long-term decisions they don't want to make.

Dr. Tracy Todd, a marriage and family therapist in Denver, says some unmarried couples don't truly understand their economic and personal motivations behind buying together. "There's a certain amount of unspoken inconsistency," he says.

On the one hand, the partners are committing to merge their finances and living space, yet they may not necessarily commit to making their relationship permanent. They may even say buying together is a way of "testing the waters" -- ironic, he says, given that couples who buy property jointly are considered married after three years of cohabitation under "common-law" rules in some states.

Dr. Todd urges unmarried couples to become clear on why they're purchasing a home together and what this means. He finds that those who later split up talk to him more about seemingly inconsequential issues related to home ownership, such as parties and decorating plans. Healthy couples discuss the financial facts of the transaction and the reality of sharing an asset.

Long 'Property' Divorce Process
Sometimes, a "property divorce" between unmarried parties can last longer than the relationship. Myna Beebe, 34, a foreign policy researcher in France, bought a home in Seattle in the early 1990s shortly after she got engaged to her boyfriend of 18 months. But the relationship began to unravel after they moved in. "We took on much too much responsibility, much too young," she says.

While the pair split amicably less than two years after their purchase and her ex bought out her equity, he still hasn't refinanced the home with a new mortgage that's solely in his name. As a result, his credit performance still affects her even though she's pursuing a career overseas. If she had it to do over again, she concedes, she wouldn't.

Whether to buy a home jointly before marriage is often a question of maturity; it can be a good idea if the couple is serious and realistic about money. Tony Hillery, a finance professional living in the Philadelphia area, and his girlfriend bought property together in 2002 before getting engaged and eventually marrying last year. As two working professionals who shared an apartment, they knew how to combine their finances, he says. They also saw the purchase as a step down the road to a permanent commitment, not as just an investment decision. "There was definitely a commitment being made in purchasing our home that we both wanted to be with each other for the long haul," he says.

Jane Hodges is a free-lance writer in Seattle.