what is this called

what is a door called where the top half and / or the bottom half can open when the other half stays closed. can I make one out of an existing door.

We have done this many times.My best advice is to get all hinges mounted and the door swinging properly, Then cut the door in two. I would not want to use a hollow core door. Make sure that the bottom of the top section of the door is cut good and square. Then make your shelf to cap over the top of the bottom section. This way if your gap is not quite parallel you can adjust it with your shelf cap.

I'll put my money on the cat...

Gooserider

Yeah the cat will find it makes a great place to survey the area.
Had a cat once that mis judged the jump and ended up overshooting the shelf..
She got stuck between the Dutch door and the screen....

Maybe get a screen door for the cat?

I have one of those,,however its an entry door to the back of the house. Makes things a little more critical since it needs to seal. In your case you wont be needing the seal between the halfs. Perhaps its worth thought to leave a gap at the bottom so that the cold air will be pulled downstairs by the blower, (provided you use one). On my basement door, i can feel the cold air spilling down the first couple steps, as i come up from the basement, just by natural gravity as the warmer air upstairs forces it under the door and down. If you do have a blower down there,,im just guessing the draft would be even more?

It might be easier to make a large face frame the size of a door. Panel the bottom and make a small door for the top of the face frame. You can still open and close the top, but the whole thing will open on the standard 2 hinges.

Matt

All I think of when I see that door is when Lucy and Ricky Richardo lived out in the country. Didn't they have one of those doors? I seem to remember a scene with one. Anybody else or am I just making it up?