sometimes
I sometimes call my father 'sir' and I see nothing wrong it.
It is respectful and shows that I respect him.
Usually when I call him 'sir' is when I have dissappointed him and feel really bad for it, and usually thats when he expects a 'sir' from me which is fair enough,but sometimes I call my father 'sir' just because I want to like the other day I was doing the dishes and he said , 'Lily could you set the table?' and I said ' yes,sir' simply because I felt like showing him that respect.I didnt feel forced or felt like I would make him angry if I didnt call him 'sir', I said it because I wanted to.
There is however a fine line between saying 'sir' sometimes and saying 'sir' on every sentence,for people who feel they must call their fathers 'sir' on practically every sentence indicates that the relationship between them isnt very good.
But really at the end of the day to address your father as 'sir' is a nice thing to do, it isnt weird and is alot more respectful than saying just 'dad', and believe it or not there are some people out there who not only agree it is respectful but who actually LIKE calling their fathers 'sir', because they love them and sometimes they want to show that by saying 'sir' 🙂