Northwestern University students Shaina Coogan and her boyfriend, Jai Broome, chose to share a place when they both moved to D.C. for summer internships.

When Shaina Coogan and her boyfriend, Jai Broome, learned they’d both be interning in D.C. for the summer, they followed a growing trend among young, urban couples: They looked for an apartment to share.

It’s a decision more couples are making. The latest national census data showed a 13 percent increase in cohabitation among opposite-sex couples from 2009 to 2010. In the D.C. area, the trend is helped along by sky-high rental prices.

Coogan and Broome, who are both students at Northwestern University, say sharing a nest for the summer seemed natural, an easy way to spend more time together while cutting costs. They estimated that by sharing a room in a Tenleytown group house and splitting utility expenses, they each saved about $450 to $600 a month.

The benefits to living together go beyond saving money.

“This is a transient town,” says Elisabeth LaMotte, a D.C.-based psychotherapist. “That makes people a little bit more likely to want the groundedness or the security that would come with sharing a home.”

Other couples would rather figure out if they can live together before committing to marriage than after.

“It’s so important to know each other’s habits,” says Timothy Fuderich, 24, a paralegal who rented a Logan Circle studio with his fiancee. “Things that may seem completely irrelevant are actually quite important when you’re thinking about spending the rest of your lives with each other.”

And don’t expect living together to be all cuddling and roses. Living with a partner is bound to be frustrating at times, says couples psychologist Michael Radkowsky. He advises couples to wait to move in together until they are beyond the courtship.

But for renters, timing a move can be tricky. “Often people make [the decision to live together] partly on a practical basis,” says Drew Permut, a relationship counselor. “They’ve been seeing each other a while, and someone’s lease is up.”

Danielle Simmons, a D.C.-based Urban Igloo leasing agent, estimates that half her clients are couples, as are a third of Urban Igloo users overall.

Simmons advises couples to write a “backup plan” in case their love fizzles before the lease ends. She tells clients to create a document detailing how things would be divvied up if they were to split, including which partner would move out and how the couple would split communal belongings.

“While it may be an exciting step in their relationship, they still both need to be very smart because they are entering a contractual obligation to one another,” Simmons says.

Couples need to be smart about more than just the financial side of things. Cohabitating couples should remember to devote attention to maintaining the relationship. That’s sometimes easier said than done when you’re taking care of an apartment together.

“Do things together that are fun and pleasurable and not just paying bills, doing dishes or doing chores,” Radkowsky says. “Create the space for the two of you to be a romantic couple.”

Broome and Coogan deemed their summer experiment a success and decided to rent together again when they returned to college. They see cohabitating as a relationship milestone, not a summer quick-fix. As a bonus, living together means not wasting time on commutes to separate abodes.

“It does make it easier if I don’t have to walk to my apartment,” Broome says. “That’s 15 or 20 minutes more that we get to spend together.” MICHELE CORRISTON (FOR EXPRESS)