Are there expected dressing norms at faculty interviews? Will a casual tee-jeans be discouraged?
In the same vein, what is expected when a student visits the campus for an interview?
While its not mandatory to wear a suit for a faculty interview, it doesn't hurt, and may actually be expected in certain disciplines. Best to ask around beforehand. I've never heard of a dress code for student visit, but something semi-formal doesn't hurt.
As a general principle, it doesn't hurt to be more dressed up than necessary. The reverse can often be embarrassing. But as with most such thing, the departmental culture is the most important factor.
The best advice for any interview dress code is, one standard of dress higher than what you would be wearing if you got the job. eg if jeans and a t-shirt is what most people wear around the office, then business trousers and a shirt is fine for the interview. If its business trousers and a shirt, then for the interview a suit and tie.
The only single right answer is that it varies.
However, there are methods that you can use to establish what the right answer might be in the particular case you have in mind.
Here's my method.
As with pretty much all human contact, the person you meet will have norms and expectations, conditioned by their culture, their quirks, the organisation they work in, the physical location of the organisation, your gender, their gender, your age, their age, and so on.
There is no general answer as to what those norms and expectations are, so research the specific person, organisation and country.
That's half the story. The other half is:
And if in doubt, wear the clothes that are smart clothes within the business world (rather than the academic world) in your own culture.
At the SLAC where I used to teach, there was a circulating story of a job candidate who showed up in a t-shirt and jeans. They were summarily shown the door.
This is even though it was a pretty casual place -- I wore a t-shirt and jeans most days during the warmer months.
Dressing nice without looking like you are going to a funeral, the prom, or a beach party is the tricky thing -- especially for women. Men can wear a dress shirt, necktie, and casual sports coat. Women have fewer dressy options so we tend to default to pantsuits.
Dressing more formally than is the norm means that you misread the university climate or that you might have been nervous and overcompensated.
Dressing less formally than is the norm means that you misread the university climate or that you might not being thinking seriously about the position.
Given the dangers of the latter, it's clear that dressing too formal is safer than dressing too informal.
First of all, I'd be unlikely to ever evaluate someone based on what they wore for an interview. But second of all, insofar as I did, more points go to the dressed down person than the dressed up one -- after all, people who dress up might expect me to do the same, and I most certainly do not want my department to become a place where there's any pressure to look "professional".
Though to be fair, I followed the above advice of "one step up from usual" when I went to interviews myself -- my daily wear is a tee-shirt and jeans, so for interviews a I wore a shirt-with-buttons and jeans.