Three problems with ridge vents: a) they let in snow (=moisture), b) they can't easily be blocked off, and c) they do not provide much actual air movement, unless you have other vents lower down and get a rising air circulation going. Personally I would not use a ridge vent for a coop, I think there are better ways of doing it (they're great for other kinds of buildings, mind you).
None of this is true, I'm afraid
Ridge vents have been standard in poultry housing the World over for generations.
They are good precisely because they don't induce much air-circulation ..... air circulation is called *draughty* where I come from.
Outside ANY chicken house there is air movement, from the lightest breeze to a tornado (we don't want those). As the air moves over the ridge vent, it is moving faster than the air inside the vent, so the venturi effect pulls air out. The first air it pulls out is the warmer, moister air that has risen.
This is the perfect solution.
They need to be positioned so that the prevailing wind doesn't blow straight in, and the wind side can very easily be baffled to prevent blowing snow.
So ... two opinions ... make yer own mind up