It may get very hot during the day, and be slow to dissipate as they go to roost.Does it get hot in the coop at night? It has 3 vent windows in the coop, but I wondered if I need to put a small fan in there?
Having a thermometer in the coop will help you track the conditions.
In your climate I'd have lots of ventilation.
Post pics of your coop and it's relation to the house, may help garner viable suggestions.