In my part of Cali summer is rather warm and have our spells of 100+. This past week we were 110 for a couple of days and 103 or more pretty much the rest of the week. I did much of what is mentioned here. They are in complete shade and can go under the coop, but that's not enough. I wet the dirt under the coop in the morning and they dig in when it gets hot. Our normal waterer is a nipple system, but when it's that hot we put water in a pan and throw in froxen 1 liter bottles so they have ice water to drink, they love it. The biggest help though really was the mister system. Ours still don't like going out under it, but it cools the whole run and the cool air rushes under the coop. At the peak of the day the chicks were just hanging out under there not even panting even with it being well over 100! The misters are the best $25 I have spent on the chickens so far. I put mine on a garden timer so the misters come on around noon-1 o'clock just as it's starting to get good and hot. Lots of great ideas here, great thread.