Hi - I'm in KY, too, and understand your concerns about ventilation. Our coop is a lofted-style gambrel roof barn with a metal roof and two screened windows, one on each side. Last year, my chickens were so hot one evening - even with added ventilation and windows open in their coop - that we had to dip them in cool water. As you can imagine, no one enjoyed that! This year, before the real heat hit (and it
just keeps coming), we did the following to make the coop more comfortable for them: built a secure screen door from wood and rabbit wire so that we can leave the front door open even at night; attached 90% shade cloth "sails" to both sides of the coop to shade the coop and also provide a shady spot underneath where the chickens and ducks could hang out; and mounted a large fan toward the top of the coop that we can adjust to point down or up.
We also leave a nipple waterer in the coop at night and put frozen water bottles in there to keep the water cool.
These have made a huge difference, even on those 100+ degree days. We rarely see anyone with wings held out to the sides or beaks open, and no dips have been necessary. I have 2 Brown Leghorns, too, with big, floppy combs - they do better in the heat than some of the other girls, but this heat is brutal for everyone.