Did they ever explain how the NTAC building changed from the one that they had in Season one to the building they have now?

The building took a shot of promicin and acquired the ability to change itself!

Sorry, I just couldn't help myself-Cassie told me to do that. Seriously, I don't think anybody has ever addressed NTAC being in a different building. Maybe they were hoping no one would notice.

I didn't notice

They walked down a long hall in the old building and ended up in the new updated place. They never went back down that hall to the old place.

LOL, I've been watching season one episodes and it's really weird. The main ops used to be two levels. I always thought they changed buildings.

From what the Companion Guide said, it was a budget issue.

I think I figured it out. Season one was Homeland Security. Season 2 gave the 4400 people their very own special branch, called NTAC. It's even on one of the quizzes that NTAC was specially assigned to 4400s. So I'm guessing it's a brand spankin new building.

But the theory room is the same. And the building looks the same from the outside. Probably, Homeland security is still in the 2 level offices, and NTAC, when crated, got its own space in the other side of the building.

The answer is the same reason the CTU set changed after the first season of 24.

Maybe they change buldings after they reorganized. Remember in season 1 they were just known as Homeland Security. Now they are a more specialized branch of Homeland Security, NTAC.

it was because of the shows budget and it was just never addressed in the show. It happens in a lot of shows. If you watch The Nanny with fran drescher--the premier epi has a completely different house from the rest of the series. Sometimes its because of bugets (as with the 4400) or with focus groups not responding well to the sets.