Thank you for this information and reasoning.I know that a sudden heat wave is much harder on people and animals that aren't accustomed to it and didn't have a chance to get adjusted than it is on people and animals that acclimate to gradually-climbing temperatures.
The good news is that the heat index isn't as relevant to chickens as it is to people. The actual temperature is the thing.
Was that 104 up at your height or down on the ground where the chickens are?
How about running to your nearest Walmart to grab one of these to set up over your coop for that double-roof effect? https://www.walmart.com/ip/Party-Te...g-Garden-Beach-Camping-Patio-S10152/666869091
Well, that reading is about halfway between the floor and metal roof. Some good news is that the adjoining shingled coop, the run of which is a lot shorter in height, has never gone over 89. And again, it's less hot than that in the dirty or mud-piled shade under the large trees where they sit all day.