My husband won't respect child...?

My daughter has a bathroom in her room. She is sick of my husband goin in her room to do number one and number two. We have another bathroom. There are four in the house. We had a fight for him to cut Back. He woke her up today to say its my house. She is 21. I told him to stop waking her up. I don't like to be woken up. I YELLED at him to stop just walking in on her. He said yelling doesn't help. So I talked soft for him to stop bugging her. She yells at him to knock first. How do I get him to understand respect her space. He has ADD and doesn't get things. I will always side with my kid. At least she has never betrade me.