Hi First winter for me and my chickens. I have 2 golden comets and 1 RIR all 3 are 7 months old. I have a coop I built from designs somewhere on the web that is 4x4x4x4. At the top are vents on all 4 sides about 4 or 5 inches tall that run all long the top. I have a door on the front of the coop that is about 18 inches high and 15 inches wide so it's a pretty big hole. with the temps getting down below freezing for the first time friday I was wondering do I need to install a door so I can close it up at night and re open in the morning. If facing the coop where the door is the roosting bar is on the left wall running length wise away from the front door. With the vents at the top all the way around and the hole so big to the door I'm afraid a lot of wind will be blowing through the coop at night however when I get up inside to clean it you can tell it's a lot warmer than outside temps. The design for the coop I used stated door is optional but I think I should probably put one on there but I'm not sure. There is no insulation on the coop and temps are going to be down in the 20's at night this weekend. I just want to make sure they are not too cold at night. Up until now hasn't been an issue. I made a door a couple weeks ago and was going to install it but the hens saw what I was doing and started going crazy. Maybe they thought I was closing it so they couldn't get inside I don't know. Anytime I clean or get eggs or do anything to the coop you would think I was killing one of them they get so vocal about it lol
I am adding a door to my little coop ASAP. If your top vents don't have any roof slanting down over them, then I would think that would be necessary to block direct wind.
Yes you need a door if for nothing more than keeping predators out at night. That is when most of them show up. I don't know how cold it gets in NC but chickens don't do well with cold drafts. So you will also want to cover some of the vents too. The general rule on how much vent space to have open in cold weather is to add more vent area if the inside of the coop starts to sweat. Don't close the vents completely, you do need to vent to let the ammonia from the droppings out or the hens will have respiratory problems. That or you will have to clean out and replace the bedding regularly. Cover the vents but leave the downwind vent open so you have ventilation without a draft blowing into the coop. If the wind changes you may want to cover that one and uncover the new downwind vent. Also as it gets colder you will need to cover some of the vent you do have open. It all depends of how cold it gets. Just down to freezing isn't that bad as long as the chickens aren't in a draft. That said chickens are fairly hardy if you allow them to acclimate to the weather. I have only 3 chickens the the same area you have. It is getting down to 10f here at nights 27f daytime temps. The coop isn't airtight, there are cracks. I have only one small 2" vent open at night but can open up a larger area fairly quickly if it warms up or i start to see sweating. The door is open in the daytime and the hens are doing just fine.