I personally don’t see a problem with an 11” x 13”. As I said, I’ve had a Midget Turkey use a 12” x 12” with no problems. That turkey was bigger than any of your chickens will be.
I’m usually an advocate for making things bigger than the absolute minimum. I do not consider 11x13 minimum, by the way. But one reason you use a pop door instead of a human sized door is to help keep rain and snow out. The bigger you make it the more weather you might let in.
I’m usually an advocate for making things bigger than the absolute minimum. I do not consider 11x13 minimum, by the way. But one reason you use a pop door instead of a human sized door is to help keep rain and snow out. The bigger you make it the more weather you might let in.