Have you talked to him about it? On one of the days your daughter isn't there, just have a quiet, non-accusatory conversation, and ask him why. It could be a variety of reasons that have nothing to do with you - maybe he's experiencing erectile dysfunction, maybe he's feeling insecure about his body getting older, or something like that. Maybe your daughter mentioned something to him about hearing you all, and he's feeling weird about it all now.
Given that you probably had sex while your daughter was growing up, it does seem odd that he suddenly won't have sex with her in the house, but you won't know unless you ask.
Just start it out with something like, "Honey, I love you and I miss connecting with you in that way, and I wonder what's happening. Can we talk about it?" Be gentle and open, and don't get defensive.
Good luck. :)
He might be down because of Covid-19 and the hit on income it creates. My husband gets very gloomy about it. Sometimes when guys are down they want more sex, but a lot of the time when they are really depressed, they don't want sex at all.
Also, how long has your daughter lived with you, is this something new?
I agree to ask him. Sometimes people are tired or stressed. It feels like work. But intimacy can also be hard if he's got something on his mind within your relationship that he hasn't talked to you about. Something he is mad at you about? I was VERY anxious during lock down. That impacts me in many ways. Is he anxious? Try spending time to connect with him lovingly without asking for or trying to have sex with him. Hold his hand, rub his shoulders but do NOT ask for sex. Just connect. Try that a bit for now to try to feel closer. And perhaps he is having a health issue? You've been married for 30 years. Could he have less testosterone or be having some equipment problems?