On Saturday night, hours away from turning 55, Bono is back in his childhood bedroom at 10 Cedarwood Road – in his imagination, at least. "Little tiny box of a room. The size of this table," he explains – because he's not actually back on Dublin's Northside, he's at a restaurant in Vancouver, telling his bandmates a story from last Christmas.

Bono's kids had made the trip to their dad's childhood home to take a picture for his Christmas present. The four of them had dressed up as a band, posing outside the house. The current owner, unaware of who they were, photo-bombed the session – this is according to Bono – they got to talking, and she invited them in to see where their dad grew up; they had never been inside before.

When the tour hit his old bedroom, the owner told his kids: "His secret box is under the floorboards," Bono says. He continues: "She pulls back the carpet. And there is a badly sawn floorboard that I used to hide stuff. And they said: 'Is there anything in there?' And she says: 'We've never looked.' "

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"Hold on a second," The Edge interjects. "She knew it was there but she never looked?"

She didn't want to invade his privacy, Bono explains . So the box is still there and the contents remain a mystery – even to him. He has no recollection of the box or what he stashed inside it.

"I'm worried about it. … Because it's stuff I didn't want anyone to see," Bono says. "I'm hoping it's explosives and not pictures of girls."

In recent years, U2 has been spending a lot of time pulling up the floorboards of its past. The result is Songs of Innocence, the most overtly autobiographical album in the band's nearly 40-year career, and also, thanks to a botched release stunt that dumped the record into millions of iTunes accounts – whether people wanted it or not – the most controversial. Mode of delivery aside, it's a project about which the band remains staunchly proud ("The only thing I regret about the album is it isn't noisy enough in terms of its sound," Bono says).

"I think there was humility in the decision to go back and realize that, actually, some of the things that we were capable of back then and some of the things we did in innocence and ignorance were actually much more powerful than we realized at the time," says bassist Adam Clayton. "And they are the reason we're where we are now."

The U2 machine has been in tour prep mode in Vancouver for weeks, and last Saturday night, the day before Bono's birthday (and also Mother's Day here) the band gathered in a round corner booth at Vancouver's Chambar to discuss the tour, the album – and keeping that creative hunger and rock and roll rage (the difference between rock and pop, opines Bono) alive, despite the cushion of the band's enormous achievements.

"I think we as individuals have never fallen into the trap of falling asleep in the comfort of our success. In so many ways, and I can't really quite explain it, the same sense of determination and vulnerability that we had when we went on stage for the first time, we still feel it now," says The Edge, the guitarist. "You could almost say that our success means nothing to us in creative terms."

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But the band bristles when the word "nostalgic" is used in connection with Songs of Innocence. This is no sentimental look back.

"We're taking the blinkers right off," says Bono. "It's more like the analyst's chair."

Indeed, events dealt with on the record include the death of Bono's mother Iris when he was 14 (she collapsed graveside at her father's funeral – a brain aneurysm) and a Dublin bombing that same year that killed 33 people and drove a friend of theirs who witnessed it to heroin (the subject of U2's earlier hit Bad). There's happy stuff too: Bono's love for his wife Ali – he's been with her about as long as he's been with the band; the influence of The Clash; the joyous discovery of Joey Ramone ("I woke up at the moment when the miracle occurred; heard a song that made some sense out of the world.")

The loss of Bono's mother (so traumatic, he tells his band-mates Saturday, that he never visited her grave despite the fact the band's early rehearsal venue bordered the cemetery) was also the subject of their breakthrough hit I Will Follow, from their debut album Boy. "It was so rebellious to sing about agape love; to sing about a mother's love – in the middle of punk rock," Bono says.

But Iris (Hold Me Close) is a more intimate affair. "Singing 'hold me close, hold me close and don't let me go, like I'm someone that you might know' is a vulnerable thing to say to an audience," Bono says.

As they prepare to take that vulnerability on the road, nothing is guaranteed. Their live show is celebrated, but it is hardly consistent, the band says. "It can be horrific or joyous. It is often both," Bono says.

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And the band members say they still get nervous about performing live. "It just doesn't come naturally or easily for us," drummer Larry Mullen Jr. says.

The stakes may be particularly high this time. Five-and-a-half years after No Line on the Horizon landed with a meh, Songs of Innocence landed everywhere last September – the iTunes invasion launching a barrage of outrage; the narrative of the record overshadowed by the kerfuffle. Now the tour gives the music its overdue moment in the spotlight. Will the miracle occur once again?

U2's iNNOCENCE + eXPERIENCE kicks off Thursday night in Vancouver, with a second show Friday.