Thank you very much for following up. Yes, I agree I will build little more than 0.5 ft2/ 10 ft2 floor space for winter ventilation (plus I may have some cracks around door jambs!). I believe that a most common advice of 1 ft2 / chicken applies for summer and not for winter. For summer I plan to have additional ~ 6 ft2 of ventilation area (~2 ft2/ 10 ft2). So altogether this will be ~ 2.5ft2 /10 ft2 of the floor OR (with 4 ft2/chicken) that calculates to be 1 ft2/chicken.That’s correct. I probably should put in more ventilation but it had t been an issue yet. If I get nice weather this weekend I will add some more on the south side.
I think @21hens-incharge is correct, build more ventilation than you think you need. You can always close shutters later.