George's wife was angry at him because he could not account for the lipstick on his collar.
You should acquaint yourself with cultures from around the world.
I think I'll stand rather than sit because my hemorrhoids are acting up again
We've decided to add on another bedroom to the house.
I've calculated that over and over, but it just doesn't add up.
The money I lost in the slot machines added up to over three hundred dollars.
George is asking for trouble.
At the end of the date, I asked Mary in.
I asked Mary out again. She refused.
I can understand why you feel that it sounds a little reduntant; however it is a phrasal verb and this is the native English usuage. Your sentence "We've decided to add another bedroom to the house" is correct; however it is more native like to hear the phrase "add on" in this case. Great comment.
It seems that "on" as in "add on" is a bit reduntant, doesn't it? I can't tell any difference between "We've decided to add another bedroom to the house." and "We've decided to add on another bedroom to the house."