I would guess the cement board was joined there. At least that row of tile has to come out. The substrate has to be repaired properly. They may not have used fiberglass tape on the joint.

Caulk won't do it. There is a structural / substrate problem. Bust out a piece and post a photo of your findings or call a professional if you are not a DIY'er

Maybe post on the building a home forum and ask there whether or not it's structural.

This reminds me of a crack right down the middle of a row of tiles that I had in my downstairs bathroom. It was caused by an uneven joint between two concrete backer boards. The solution is to make your tile substrate even.

Everything CTECT said.

Thanks so much for all the advice guys! This is super helpful!

I'm reluctant to smash out a tile, mostly because of the hassle. Need to find the same tile somewhere, etc. If I "ignore" the issue, and just caulk over the crack, what's the worst that could happen? the wall would split apart even more? A safety issue?

Thanks guys!

erick

Water could get behind the tile and possibly leak into the wall cavity - perhaps.

Looks like too nice of a house to just ignore. It's not going to get any better, and when you sell the house you will have to get it replaced.

Even though the home is 5 years old, I'd ask the builder to come over, and take a look.

If I "ignore" the issue, and just caulk over the crack, what's the worst that could happen?

Second worst: Water leaks behind the caulk, destroys the studs behind the tile and the joists in the floor, and you have to rip out the whole shower stall, wall and floor and replace everything. And do mold remediation.

Worst: Water leaks in there, destroys the studs behind the tile and the joists in the floor, and you step in the shower one morning and the joists give way and you and the shower stall end up in the basement.

No fooling, this happened to a friend ... he caulked around the base of a leaky toilet because he didn't want to have to remove/replace toilet and fix the problem. About a year later he sat on the toilet and ended up in the basement because the joists had rotted. The paramedics were amused.

lazy_gardens, thanks for sharing that story because I think a lot of people don't realize how quickly an issue like this could get serious-I know I didn't. I hope your friend wasn't seriously injured and could get his pants up before help arrived!

His pride and dignity was the most seriously injured.

... he didn't know the house even had a basement before that. The door had been walled over and there was no mention of it in property records. They are RARE in Phoenix.

So after he fixed the floor of the bathroom, he fixed up the basement as a media room and home gym.

wow, that's incredible. thanks for sharing, lazy_gardens!

I was laughing out loud, case of literally finding luck in an unlucky situation!