When building a coop you don't want it drafty, but you do want good ventilation. Where is this line drawn. Is the ventilation purely from "rising heat" or is it caused by a source of air flow other then the vents that allows the air to flow between. Thanks for your time.
My coop just has vents (and of course open windows in the summer). A lot of people also use cupolas or those whirly bird vent things on the roof. I consider it "drafty" if it blows accross the roosting birds.
I'm not sure of the logistics of ventilation, but we read where the coop needed ventilation in the ceiling, so we put vents in the overhang of the roof and left them open inside the coop. We ended up putting hardware clothe over the opening inside though, as our bantams were flying up there and laying eggs!!! We also cut a window in the north and south wall in which we put hardware clothe over. They are just a little higher than the roosts. In the winter,we screw old windows over them. Until we acquired the windows, we used heavy mil plastic tacked to the outside. They both work great in keeping out drafts. I just like the idea of lots of fresh air in the coop. Not sure if this helps or not, but this is what we did and it works really well.
Pretty much the line is drawn seasonally. A "draft" in the summer is good, that means a cool (not so much recently) breeze blowing on the birds through a window or a wall vent, either high or low. A "draft" in winter is bad, that means icy air blowing on the birds who are already using energy to stay warm as it is. But in winter, you still need a way for 'warm', moist air (from respiration, droppings, etc.) to escape the coop, so vents up high (above the heads of the roosting birds) are best, or vents far away from where the birds are roosting. Hope that helps a little.
Yes, the ventilation is just from rising heat, or can be. That's why it's good to have at least part of it at or near the highest point of the coop. I used to think there needed to be an incoming air source low in the coop, but that is incorrect, as the air exchange will occur entirely at a top vent, both in and out. Draft refers to air flow which blows on the chickens, particularly in cold weather. This time of year, what would be a draft in winter is a welcome breeze. Have you see this excellent article on ventilation? https://www.backyardchickens.com/web/viewblog.php?id=1642-VENTILATION
An inlet low in the coop away from roost and outlets high will maximize air circulation without causing drafts. Also orienting the inlet so it's not on the prevailing winter wind side alleviates drafts. Personally I'm against windows but an extra vent that can be opened in heat of summer works the same way, though if your inlet area and outlet areas are of same size you've maximized the circulating air flow already. It doesn't take a whole lot of vent area to circulate fresh air needed per chicken. If the coop starts to smell, is muggy or as temps drop below freezing and you see frost on wall or ceiling then you've not enough vent. 0.5 cubic ft per minute each chicken needs to vent out the fumes of refuse for good respiratory health and moisture to prevent frost bite in winter.
Also a vent hole, covered with hc of course, on the low end of the roof at the soffit, helps tremendously to remove the hot air as it flows up the roof rafters and out the ridge. I helps keep the bottom side of a metal roof dry too.
