My main coop is a 12x16 converted shed with 20-something square feet of ventillation that's way above the chickens' heads when roosting. 12 chickens in there currently; never had respirtory issues with that or even my smaller, more minimally ventillated coops (ignoring a couple of dingy birds snorting the odd piece of feed that I then have to pick out...). Never had mold inside that coop or my various smaller ones despite the riddiculous humidity here. Outside though is another matter for any surface that has regular contact with rain/snow/dew/frost. I actually have to be really careful with outdoor beddings like straw because of that. My husband is building a new structure right now that had some exposed untreated wood, and even in this winter's bitter cold it got some mold going because of melting snow in the sun (I don't think it was even ambiently above freezing when the mold set in, just sunny!). But I think there must need to be more than high ambient humidity with otherwise dry surfaces to get mold growing since I've never seen it here on protected surfaces that don't also get some sort of more direct moisture.If the humidity is that high where you are, and in your coop too, we had issues when we first started about 9 years ago. The windows would weep and ice over and the walls ran it was so bad. We had zero ventilation, doh, and hubby didn't believe me in the beginning until he saw that. I am surprised we didn't kill any chickens as mold can start growing at 70% humidity, and higher than that, they'll be susceptible to URIs, plus the ammonia that builds up will cause those too.