But see, that’s just it... most people don’t realize that the two things are related.
It’s the same way someone will assume that they need a heater in the coop if their birds get frostbite. But if they’re using a pre-fab coop, as advertised, with too many birds and without any add’l ventilation... the problem isn’t the low temperature— it’s that there’s twice as much hot, moist air being breathed into the space and no where for it to go, so it precipitates onto the chickens and freezes.
Who tells them this, though? It’s not intuitive. Frostbite comes from cold, right? So, add heat— problem solved. Except cold [alone] wasn’t the whole problem, just the last step in the cascade.
Think about it... The idea of raising chickens appeals to you, so you buy a coop, assemble it according to instruction, and use it the way it said you could. Then you begin seeing illness in your flock. Maybe you lose a couple. Others get sick, then better, then sick again... it seems like there’s always something going around the flock. If you’re really lucky you have access to an avian vet, but they diagnose pneumonia, maybe coccidia, and at one point even worms. They certainly don’t ask where you got your coop, or how much ventilation you have.
There is
literally no-one else out there pointing out that prefab coops aren’t living up to the manufacturers’ claims. Even most of the bad reviews cite things like: ‘the paint faded in one summer’ or ‘the wood is much thinner than expected‘, etc.
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That said, I think it’s worth noting, the coop from the OP isn’t really a “pre-fab” coop in the usual sense of the term. Rather, it’s designed by a craftsman (who may or may not hold Amish beliefs

). I believe it’s flaws are probably the result of it being designed by someone who was more likely a cabinetmaker or carpenter, rather than a chicken farmer. So it is a very attractive coop visually, but lacks a few key details that a chicken keeper might find critical.
Ventilation isn’t hard to add. It could use some extra reinforcement with hardware cloth, and may need better latches... all that is relatively simple enough to augment.