After being on the air for five years, you’d think creating the world of a TV show would get easier.

Not so, says “Boardwalk Empire’s” head of set design Bill Groom. “In fact, this upcoming season has been one of the more challenging ones yet.”

Even given the show’s rich, elaborate settings, it’s not a problem unique to “Boardwalk,” he says. “That’s true with every project you work on. Whether it’s a sequel or a new season, there will be similarities and differences with each new installment.”

Groom started working with “Boardwalk” in season 2, as the show was transitioning from one architectural era to another, and the creators were looking for someone to help them enter the new look of the 1920s.

“Season 1 was very stately and crisp, but it was necessary for that to change as the period did,” he says. “The end of that decade was the end of stateliness in the Edwardian sense.”

Since then, he’s had his work cut out for him, as he’s had to find homes for iconic characters like Al Capone, Chalky White and Arnold Rothstein — as well as “travel” to locations such as the Irish countryside (for which Brooklyn stood in) and the Tampa Bay coast.

Rather than building a house to fit the period, Groom and his crew spent hours researching specific areas where houses fit that era — and then restoring the building to look as if it was just constructed in the 1920s.

“One of the first items I worked on was finding Jimmy’s (Michael Pitt’s character) house,” Groom says. “We ended up finding one on the water that was built in 1918. It needed a lot of restoration: We replaced and added 300 window panes, but that was an example of what we wanted to do going forward. New York is kind of amazing when you get outside of Manhattan because of all you can choose from that already exists.”

He says he’s learned so much through his years on the show that he doesn’t have to do as much research anymore. “I can remember in that first season spending so much time researching things because the whole idea was staying ahead of the material as it was being written,” he says.

Now that the show’s entering its final season, it’s that research that he’ll miss the most. “I love doing period pieces,” Groom says. “You discover things about how people lived then and how inventions came along that it becomes a very integrated process that I really enjoy.”