To add on to this idea, we raised the half door just high enough for the cat to squeeze through but dog couldn't. We didn't want my elderly cat to have to jump to basement side with the stairs right there.
Originally Posted by purplemem
For the cat/dog problem. We solved it by DH making a half door, sometimes called a Dutch door, out of pegboard. The doggie can look through the holes and see me. The cat jumps over the sill and can come in the room. If making one from scratch sounds too intimidating, cut a hollow door in half and place a shelf on top for kitty to perch. It would already be prepared for the hinges. It really works for us.