Then Griffiths takes off for three to four months touring Australia and, increasingly other parts of the globe, promoting his new book, talking and entertaining his multitude of young fans, recharging the creative batteries and keeping a weather eye - and ear - out for new ideas.
"Everything we do is about having a conversation with our audience. I know when it's time to start a new series through the conversations I have with the kids who tell me whether they love the latest book or ask when I'm going to move on to something new."
Because Griffiths is criss-crossing Australia, it takes days to arrange our interview. When we talk, he is in a car parked outside a Brisbane school where he has 35 minutes before speaking to 900 children who want to hear about the recently released The 52-Storey Treehouse.
Like three previous Treehouse books, it's about responsible and resourceful Andy and his more wayward friend Terry, who live in a mind-blowing and ever-expanding treehouse where they write books together. They are distracted by things like having to rescue their publisher, Mr Big Nose, and sensible friend Jill from marauding vegetables but their treehouse has features like a watermelon smashing room, a make-your-own pizza parlour, rocket-powered carrot-launchers, life-sized games of snakes and ladders and a ninja snail training school that aid their rescue quest.
Griffiths may have a reputation for books packed with weird and wonderful inventions, impish kids, dastardly villains and slightly lewd, often self-deprecating humour but he is a deep-thinker who takes a serious and methodical approach to work. His maxim is "comedy is simply a funny way of being serious" (a quote from English actor and author Peter Ustinov).
"The comedy comes not from having someone do something funny; it's more about having someone else watching someone do something funny. That's what I have learned from all my years of serious study of comedy and creativity. We enjoy Andy's consternation at Terry's silliness. Andy is the more focused and serious one; Terry is a bit more lackadaisical and brings random chaos to a project. The humour must have logic to it and the story a good structure; in the Treehouse books, there is always a problem to be solved."
Griffiths is serious about comedy - when the book tours and public speaking engagements picked up, he extended his studies to "humour-versity" to learn about stand-up comedy.
"Because I write funny stuff, I found the kids expected to laugh. I like to let the kids dictate the talks so there's spontaneity and improvisation, but it's 'prepared spontaneity' ... "
His has been a long writing life. Now 53, Griffiths started writing when he was just 6. He says he wasn't the class clown, but could be found close to the back of the schoolroom drawing cartoons and captioning them to make the other kids laugh and, occasionally, shock them. "If I were a kid today, I would definitely have a blog."
He became a singer-songwriter in a punk rock band, his stories transforming themselves nicely into lyrics. When he decided he would rather be writing than performing, he became an English teacher. In the classroom, he met kids who claimed reading was boring. "I was shocked because I had grown up in a house well-stocked with books and I loved reading because it meant I had this imaginary second life, but these kids had never had a good experience with a book. I thought they were impoverished."
Griffiths wrote short stories and turned them into books to make his students laugh and to show them reading and books were most certainly not boring. He says he wrote intuitively about things that would have either interested him or made him laugh at their age. Because he enjoys material from all around the world, he didn't go down the track of adding deliberate Australian elements to the stories - although one book was about killer koalas from outer space. That said, he thinks coming from Australia influenced his style and sense of humour in immeasurable ways.
"We have such freedom to be larrikins and laugh about the sort of stuff that might upset other people who take things far more literally than we do."
His books earned him a dedicated following of young fans so he started photocopying collections of his stories to sell at Melbourne markets. He'd sell 40-50, at $1 each, in a day and have customers returning to ask when the next one was coming. The funnier ones outsold the more serious by 5-1, so Griffiths realised he was a comedy writer.
But his approaches to publishing companies were less successful and Griffiths tells budding writers he meets that they have to be resilient and prepared for rejection, something he spent years dealing with. He wrote to publishers declaring he was the author of a series of 10 pocket books which had sold well. An exaggerated truth, it cut no ice with publishers who told him his roguish humour was difficult to grasp and they couldn't see a mainstream market for such comedy.
"But I knew there was because of the feedback I was getting from doing my own selling."
He eventually wore them down and was teamed up with Terry Denton to produce a book, based on his original photocopied ones, as a light-hearted educational one. Griffiths wasn't overly keen on "educational publishing" but figured a publisher was offering a chance so he might as well take it.
Just Tricking, the first of eight in a series of short stories, appeared in 1997 and was narrated by young Andy. More significantly, Denton, an experienced illustrator, took a liking to Griffiths' work and, by attaching his name to the next series of books, was able to help his new friend and creative partner swing his next publishing deal.
The result was a series called The Bad Books, which Griffiths describes as his "punk rock album". All sorts of humour came out, including a passage where a naughty little boy, Willy, sets fire to a cat and is not punished for his cruelty. It sparked an outcry, mainly from parents who weren't concerned Willy was self-harming by burning bits of his own body but outraged at the malice toward an animal. It was a valuable lesson that you can take a step too far and risk alienating, perhaps not your target market of 7-13-year-olds, but the people who buy books for them.
"We found the edge of the humour and went over it, but I learned if an innocent victim suffers and the perpetrator is not justly punished, that's no good. There needs to be a moral balance which is restored. Bad things can happen but the bad person must be seen to get their just desserts. We've since removed that passage from later editions of the book because it was upsetting people - and that upset me."
After all, that goes against everything he tries to achieve. "It's always very cool for me to make someone laugh, whether it's my wife or my friends or kids at school," says Griffiths. "I never get sick of that reward of getting a smile out of somebody and I'm lucky my books do that on a large scale."
The 52-Storey Treehouse (MacMillan $17.99) is out now.
