The Lumineers’ self-titled album, bankrolled by the band’s Seattle-based management company and released by an independent Nashville label, has spent nearly six months on the U.S. chart, riding the shout-along track “Ho Hey.” The set, which has never ascended higher than No. 11, had sold 278,000 copies through the week ending Sept. 9, according to Nielsen SoundScan.

After a slow-building rollout — buttressed by active club touring; prominent use of their tune “Ho Hey” in national TV spots; radio play on NPR and other outlets ; and a popular YouTube video — the band has kicked off a U.S. theater tour that includes 14 sold-out dates. The group is now widening its radio audience in the top 40 arena.

That number, attained over 23 weeks, dwarfs the initial sales of the biggest slow-rolling hit in recent memory: At the same point in its sales history, U.K. band Mumford & Sons’ “Sigh No More” had sold just 95,000 copies (to date, that tenacious 2010 album has sold 2.4 million).

Paul Roper, president of the Lumineers’ label, Dualtone credits Mumford’s success 12 months earlier for helping prepare the ground for the Lumineers. “We’re in the middle of this kind of roots rock revival, where the timing for the Lumineers was just perfect,” he says.

The group’s singer-guitarist Wesley Schultz is also quick to credit Americana precursors such as Mumford, the Avett Brothers and Old Crow Medicine Show for opening the door for the Lumineers.

“We feel gratitude toward those bands. They affected our trajectory, without a doubt, as far as how many radio stations would be able to play the songs.”

When Mumford’s “Sigh No More” finally climbed to the top of the U.S. chart early last year, the Lumineers were still relatively recent Denver emigres. Schultz and drummer Jeremiah Fraites had moved there from New York in October 2009. They had begun playing together after the 2002 overdose death of Fraites’ brother Josh, Schultz’s boyhood friend. In Colorado, they were joined by cellist Neyla Pekarek.

They were typical indie road warriors. “We stayed at people’s houses, crashed on floors and couches,” Schultz says. “We did a couple of rounds of touring, and then we got a residency in New York City.”

By the time of their March 2011 stand at New York’s Living Room, a video of a Lumineers house-party set had caught the attention of Christen Greene, g.m. of Onto Management, a Seattle firm headed by partners Dave Meinert and Brent Stiefel. Greene decided to fly to New York to attend one of the group’s no-cover shows.

“March in New York isn’t a time when a lot of the industry is paying attention to what’s happening, because everybody’s preparing for South by Southwest,” Greene says. “I showed up expecting to see a ton of suits, and there was nobody. It was probably 30 or 40 of their friends there, watching them play. They just blew me out of the water.” Greene offered the band a management deal that night.

The group, which had been selling a self-recorded four-song EP following gigs, had cut a second EP, but Onto wanted to upgrade the sound.

“(Management) said, ‘The songs are great, (but) don’t put it out,” Schultz says. ”We want to put you guys in a bona fide studio and put out a full-length record, and we’re gonna float that money.'”

“The Lumineers” was cut with producer Ryan Hadlock at Seattle’s Bear Creek Studio.

Says Greene: “Monday through Friday they were in the studio, and Friday, Saturday and Sunday they played (club) residencies in Portland, Seattle and Bellingham. It was really an insane schedule, but it enabled them to build a new region.”

By the time the album wrapped, blog coverage of a Lumineers house concert had attracted the attention of Americana/country label Dualtone.

Roper says his first experience with the Lumineers was not unlike Greene’s: “We saw them at Eddie’s Attic in Atlanta. I guess this was November of last year. There were 35 people in the audience on a weekday, in a market that they had no familiarity in. But you could see the potential.”

As Dualtone was finalizing a deal with the Lumineers in December, the band secured its first significant sync use in a TV show: “Ho Hey” was included in a climactic scene in the CW series “Hart of Dixie.”

“That was the point where you could see the reactive nature of the band’s music,” Roper says. “You could see the social media immediately start, and the uptick on Facebook. … The band played in L.A. shortly after that, and had two sold-out shows at (Hollywood’s) Hotel Cafe.”

Dualtone’s release of “The Lumineers,” distributed by Warner Music’s Alternative Distribution Alliance and digitally by Ingrooves, was prefaced by a “Ho Hey” video.

The clip, in which the band members cavort among fedora-wearing fans who sing along with the song’s exclamatory hook, drew a page from the group’s onstage playbook: “They go out into the audience and play a song with the crowd gathered around,” Roper says.

Greene notes that Viacom looked at the clip and fell in love. VH1 named the Lumineers as its “You Oughta Know” artist of the month for July and August. The video has racked up more than 6.5 million YouTube plays to date.

“The Lumineers” sold at a steady 5,000-7,000-unit clip each week through early summer, buoyed by the use of “Ho Hey” in commercials for the Bing search engine and (in an instrumental version) for Blue Moon beer. Sales were stoked by features on National Public Radio.

Roper and Greene both credit John Richards, morning man at non-commercial triple-A station KEXP in Seattle, with kickstarting “Ho Hey” on the air.

“You always wonder if you have a great song for radio, and early on we were saying, ‘I wonder if this is too short,’ because it’s two minutes and 40 seconds,” Roper says. “But what ended up happening was John started playing it back-to-back. You could play it twice. People really responded to that.”

Triple-A and alternative stations in markets like Denver and Boulder, Colo., and Albany, N.Y., soon followed suit, and starting in July, “The Lumineers” consistently sold in excess of 10,000 copies per week. A one-day $1.99 “Gold Box” deal boosted sales to nearly 30,000 for one week early that month.

With sales of “Ho Hey” topping 700,000 and samplings of the song audible in a trailer for “Trouble With the Curve,” Dualtone has now moved its campaign to top 40 stations. Outlets in such markets as Las Vegas, Nashville and Sacramento, Calif., have added the single.

On Sept. 20, the Lumineers, who began 2012 playing 350-seat clubs, kicked off a U.S. tour that includes 14 sold-out dates, including two at Hollywood’s Fonda Theater Oct. 1-2.

Greene says the band’s upcoming bookings will be even bigger: “We’re already getting U.S. festival offers for (next) summer. For the venues for early 2013, we’re looking at 1,600 to 2,500 (capacity). I feel that’s on the smaller end. The biggest we’ll go in January in the U.S. will probably be around 3,000.”

While Roper sees the band continuing to be rooted in Americana, the scope of its current success is broadening the marketing canvas.

“Their career is going to be in the modern rock and the triple-A space,” Roper, maintains. “But because of what’s happening with the project, top 40 is going to become a huge part of this process.” The takeaway: The Lumineers have racked up a quarter of a million in sales — via hits on YouTube, touring and song placement — without hitting the national Top 10.