Stupid question - how big for a chicken door

[blackdog043]

I have a 13 x 14 opening. I used a cutting board for the door and shelf brackets for it to slide up an down in. I have a metal bar that locks in place so it can't be lifted up when it's closed.

 

[Ol Grey Mare]

I have a 13 x 14 opening. I used a cutting board for the door and shelf brackets for it to slide up an down in. I have a metal bar that locks in place so it can't be lifted up when it's closed.

We used sliders too. ...Ours is set to where the bottom goes down about 4 inches into a framed area that keeps it from being able to be lifted by the bottom lip. Can't find good inside pics on my phone

 

[blackdog043]

We used sliders too. ...Ours is set to where the bottom goes down about 4 inches into a framed area that keeps it from being able to be lifted by the bottom lip. Can't find good inside pics on my phone

Yes, mine goes down below a board also, plus the bar across the top.