I have two coops. One that is occupied by my hens, one that is currently vacant. Both coops face west, are made with the same supplies (plywood) and are painted with white exterior "barn paint". They are even the same design, shape etc, with the one being about 4 ft longer than the other. They are also only about 10 feet away from each other. The coop that is vacant, has black/green mold dots all over the outside, and a little bit on the inside. The coop my hens are using, does not have any mold inside or out. The only difference is the one that has the mold, the frame was made using old wood pallets,we got from the local feed store, that had been stored in their warehouse. The pallets did sit outside a bit before we used them, and I do remember a few of them having a little mold on them, but I drenched them in bleach water and dried them out before we built with them. I thought maybe the coop didn't have enough ventilation, but most of the mold is on the outside. The mold is the heaviest on the exterior wall facing south. However, there is no mold on the exterior wall facing north. Some of the coop is painted on the inside, and there is a little bit of mold, but only on the painted walls. Again, the mold on the inside is quite minimal. I decided to scrub the coop down, inside and out, with bleach water. That took care of most of it, except the south side, which I think is basically just stained now. I plan on getting some exterior "Kilz" paint and paint the coop again once the weather warms up. I'm a little nervous, though, because I have chicks coming this week, and had planned on putting them out there in the next couple of weeks. I also have a little tiny coop, that I just use for storage, that has the same issue. However, that little coop is made with painted particle board, so I'm not surprised that is isn't in great shape. That too has mold on only certain sides, on the outside, and is painted with the white barn paint. Any ideas of what could be causing this?? This is so frustrating!!!! Any advice would be greatly appreciated!! Thanks!!