I would never seal up a chicken barn tight, trust me. I sealed up gaps against rain and drafts. I want my ventilation up high. If you've seen my other coops, they always have good size ventilation openings at the tops of walls, all winter long. In this barn, there are 5 windows, a 2.5" x 6 ft gap at the top of the roll-up door, plus air flows inside the box trim all around the building (you can see daylight at the top of the walls). I have already discussed more ventilation with husband, who usually balks at "more" of anything, but the possibility of a wall-installed exhaust fan in one of the gables is still in play as well as barn hanging fans of some sort. I'm not going to do it until I'm at that juncture. We have a long, long way to go before chickens will inhabit this building.
I spent a little while ago placing the steel U-posts back at the fence line where they used to be, now that the pasture work is complete. We have the chain link gate installed again and ready for the posts to be hammered in and the fence re-strung, but DH has messed up his fingertips with the concrete work and is out of play today for the most part.
Sound perfect. I have a small coop. I have thought about putting in old server fans to keep it cool in the summer.