Take the whole thing off if at all possible...can you see the edges of that board?When me and my husband were looking at it that’s exactly how it looks. Like those nails hold that board in and it runs the length of the coop. His idea was similar, to just take the board out or cut holes in it to get the appropriate ventilation.
I can take more pictures tomorrow too. Some from the inside this time and some farther away should help right?
Hopefully there are no covered/hidden nails.
Pics from just the inside.