A rendering of a plan for the exterior of what will be the new Keegan Theatre, currently the Church Street Theater, in Dupont. The company closed on the deal to buy the property June 21 and plans $1.5 million in renovations. (Stoiber & Associates)

It’s hard to weigh the impact of the small Keegan Theatre company’s purchase of the Church Street Theater without first doing some, well, “bathroom math.”

The theater seats 117, and lately it’s generally been pretty full. Keegan’s popular production of the musical “The Full Monty,” which closed this month, had a cast of 18, plus a handful of musicians. The 1905 building features only what Realtors call two “half baths” for everyone’s satisfaction.

“Intermissions have been lasting half an hour,” laments Keegan producing artistic director Mark Rhea during a tour of the cramped quarters.

Upgrading is not why Keegan bought the theater, a two-story brick structure that easily fits on its quiet side street just east of Dupont Circle. But the prospect of better plumbing has the troupe pumped.

“Everyone’s super excited about the bathrooms,” says performer and director Kerri Rambow, a longtime company member. “I have a feeling that’s going to be the big naming opportunity.”

Production image from “The Full Monty” at The Keegan Theatre. (C.Stanley Photography)

Indeed, there is a lot of cash to be raised for the $1.5 million in renovations Keegan has planned. That’s a big lift for a non-Equity organization without a fundraiser or managing director, with only two full-time staffers and with an annual budget of only a half-million dollars a year. An anonymous donor bought the theater for $1.9 million in a deal that closed June 21 — Rhea’s birthday.

“Six months ago, we didn’t think this was going to happen,” Rhea says navigating amid clutter so overwhelming it would make a teenager blush.

The Church Street Theater’s small lobby never holds more than a dozen people comfortably, but, two days before the sale’s closing, it is overrun with props, costumes, furniture and a piano, plus cases of champagne, beer and bottled water for the impending celebration.

On top of that, the perpetually busy troupe is in transition between “The Full Monty” and David Lindsay-Abaire’s Pulitzer-winning, marriage-rocking drama “Rabbit Hole,” featuring Rhea and his wife, Susan. (It was scheduled to open Friday.) There is no place to put anything; Church Street, a hub of Washington’s small-theater scene for decades, has nary a suite of offices or much else in terms of creature comforts. Staff members and actors hang out in the alleys.

So Mark and Susan, Keegan’s associate artistic director, clear out space in the lobby for a couple of chairs as they talk about taking the plunge.

“We’re in depths we’ve never been in before,” Susan says about the purchase. “A lot of this legalese was confusing. It puts a knot in your stomach.”

Yet it was a sort of homecoming for Keegan: Its very first show, in 1996, was “A Streetcar Named Desire” at Church Street. The troupe then bounced around Arlington County for a decade, performing “Hamlet” in a church basement (its headquarters for a period) and “Man of La Mancha” in a high school auditorium.

Keegan briefly partnered with Washington Shakespeare Company, recently renamed WSC Avant Bard, in Crystal City’s Clark Street Playhouse. They produced at Theater on the Run, a small, county-operated space in Shirlington.

“We couldn’t sell [tickets] in Arlington,” Mark Rhea says.

After a promising residency deal in Old Town Alexandria fell apart, Mark Rhea came back to Church Street, giving away the bigger portion of a 60-40 box-office split just so he could produce the company’s next show. With its central downtown location and moderate size, Church Street has always been coveted by small companies, and it had a shaggy heyday in the 1970s and ’80s as the site of New Playwrights Theater. (For an unbridled trove of New Playwrights history from writers, actors and designers who lived through it, see Harry Bagdasian’s Web site, hbagdasian.com.)

The building even had a famed cat named Gus for 16 years.

“He made more appearances onstage than just about any actor,” says longtime Church Street manager Edward McGee, “especially when New Playwrights was there.” McGee had been on staff since 1987, when New Playwrights hired him to work the box office; less than two weeks ago he turned in his key.

“It was strange to take the key off my key chain, having had it on so long,” McGee says. It’s he who puts the building’s construction date as 1905.

Max Berry, a lawyer and former chairman of the Pennsylvania Avenue Development Corporation, had bought the building in 1988. When New Playwrights petered out, Church Street was largely a rental house until Keegan became the full-time tenant in 2009. By then, Keegan was doing so well there that keeping a foot in Arlington no longer made sense.

“It costs more, but we make more,” a board member pointed out.

Mark Rhea says the latest terms of occupancy for Keegan included $5,000 a month in rent, plus another $10,000 monthly in expenses to run the building. The bulk of Keegan’s income is drawn from ticket sales, with tickets moderately priced at $35 for plays and $40 for musicals. (For the run of a show, actors are paid a percentage of the box office or, sometimes, a flat stipend that comes to several hundred dollars, which is standard in Washington’s non-Equity circles.)

The monthly bills help explain why Keegan produces its mix of classics, premieres and musicals at a near-frantic rate. Eight shows a season has been the standard since the company produced an eye-popping 10 in 2009-10.

The Rheas think Keegan’s recent success boils down to two factors. “Residency,” Mark says — a fixed address so the public can identify an organization and settle in. The second thing: “I started listening to my audience.”

That meant mixing up the offerings. Keegan’s aggressive Irish streak has included world premieres and revivals of such daunting works as Brendan Behan’s “The Hostage”; the company has toured to Ireland 13 times. Yet Mark Rhea says he would sometimes hear from board members and audiences, “Oh, you’re doing the heavy Irish thing again.”

“We were being asked to lighten up a bit, for sure,” says Susan, who by day is the Web site manager of Alliance for Justice.

Keegan’s musicals have made a bigger splash since the hit production of “Rent” that the Rheas co-directed in 2009-10. Last season, they showcased “Spring Awakening,” and this winter, “Cabaret” was a sellout hit.

The programming can be achingly mainstream: Arthur Miller’s “All My Sons” opened this season, “A Few Good Men” is up next, and “Hair” is on the bill next year. But more premieres are coming, too, and though “Character driven, audience proven” is Keegan’s slogan, the Rheas have no clue whether people will turn out for “Rabbit Hole,” an elegant study in parental grief.

They rarely find time to act together anymore, although they got married on a stage in Galway, Ireland, during the 2003 Keegan tour of “Glass Menagerie,” and had bonded playing the leads in “The Taming of the Shrew.”

“She head-butted me and broke my nose,” says Mark, 49, a plain-talking Texan.

“Whatever,” Maryland native Susan, 43, shoots back. “It’s nonsense to blame me. We were doing a wrestling scene. And my head hit his nose.”

“Rabbit Hole” seems to reflect their taste — serious, straightforward — even if their anguished roles could be tough for a real married couple to live with. “I don’t think I’d want to share it with anybody onstage but Susan,” Mark says.

“It’s more reassuring working with you,” Susan says fretfully. She worries that such emotional comfort might actually be a problem, because the husband and wife are supposed to be at such harsh odds in the play.

Keegan hopes to shut down for only six months next year during the proposed renovations, which will feature new dressing rooms, rehearsal space and a classroom, all underground. And about the bathrooms: There will be a total of seven (five for the public, two backstage).

Rambow suggests there is a family spirit that has pulled Keegan this far and will keep it pushing forward. “We all work together, play together and fight together like a group of brothers, sisters and parents,” she says.

Mark Rhea uses the same terms. Waving his arm rather humbly at the chaos inside Keegan’s theater, he says, “I didn’t think I could have a family this big.”

Rabbit Hole

by David Lindsay-Abaire. Through July 21 at the Church Street Theater, 1742 Church St. NW. 703-892-0202; keegantheatre.com.