Extremely helpful information, @Ridgerunner !
I'd like to add a few, small addendums:
Important point!
I had enough random things in my run last year to provide shade at all times last year, but in the new run I have plans for this summer that include both:
Pallets up on blocks to give...
And here is why we like to know your general location -- climate matters.
My birds are acclimated to heat. For them 85F (29C), is a cool day in mid-summer. :D
A sudden spike of heat is more dangerous than a gradual build-up of heat with time to get used to it.
Also location matters for...
Do they have access to shady ground where they can dig themselves a nice, little foxhole?
That seems to help my flock cope with the 95-95 summers we get (95F, 95% humidity).
https://www.backyardchickens.com/threads/even-the-babies-are-dug-in.1484952/