All that I've read says 'plenty of ventilation but no drafts'. So..... what is the difference? Placement, size, what?
What is the difference between 'Ventilation" and 'Drafts"??
Draft is a breeze hitting them.
If you are just north of Houston, it's not really an issue with you. I still would like to keep direct breezes off of them in the winter and mainly during the worst of the thunderstorms you will see, but you could get by with one entire side of your coop being wire. Just put their roost sort of back in that nook formed by the three solid walls.
For us mortals sometimes faced with actual cold weather, the way to handle the problem is placement. Have the ventilation openings higher than they are when they are on the roosts. The air will move above them and take away all that nasty stuff, which is lighter than air, by the way. You do need openings higher than the chickens to get rid of it.
Any real drafts will be over their heads.
Where you are your real enemy is the summer heat. A lot more chickens die from excessive heat than from cold. For you, a breeze hitting them in the summer is a good thing, not a problem.
Just like real estate the answer is location location location.
You need enough ventilation so moisture does not build up within the coop- and this ventilation must be far enough from the roosting area so drafts do not blow directly on the birds when roosting. Ventilation at roof level is a good thing when roosts are at mid coop.
Vents can be at midcoop if birds are induced to roost low at floor level.