Wintering Coop Question

[Angaramiel]

My husband are designing our coop. We will not be getting any hens until next Spring.
We're only planning three hens, two mostly layers, one cute little bantam.
The hens will be free-ranged, even in winter, so we are not planning a giant coop.
We have decided that our coop will need to portable as it will be moved twice a year. In the summer it will be among our willows and ninebarks to keep cool, and in the winter we will move it to be by our backdoor near an outlet we have in case we need to use the heat lamps.
Our climate is an ag zone 6. We do get snow and at times can be stepping in three feet of fresh (though not too often for that). Where the coop will be does not get a lot of wind but gets great sun in the afternoon in the winter.

We're designing a coop sort of like this one: https://www.backyardchickens.com/a/cottage-chicken-coop

My question is this: winter. Lol. That little ramp to the bottom with the opening in the floor, would that need to closed on the super cold nights?

 

[MoonShadows]

Since you coop will be on wheels, unless you are parking it on a solid foundation like concrete, paved walkway, etc. I would close that door every night, not just cold winter nights; otherwise, you might get a predator who will dig under and find the door left open for him.

 

[Angaramiel]

I don't really want to get into all of the design changes for that coop, but assuming the run is completely enclosed and predator proof...

 

[MoonShadows]

I guess you can, then. Since most predators come out at night, and since the chickens sleep in the coop, I feel safer with my coop being predator proof, too. It seems so many times we hear of a predator breeching the security of a run. But, let others respond and see what they have to say.

 

[cknkids]

I like closing the pop door when it drops below freezing; not sure if it helps the girls but I sleep better. After a year, I’m still trying to under stand the difference between ventilation and drafts. I'd also encourage you to check your numbers. The Hawaiian Cottage Coop is adorably sized for bantams, I’m not sure it’s adequate for full sized hens, at only 7.5 sq ft. I guess you could consider it a 2 story house with a total of 15 sq ft, and then it’s plenty big. Many use 4 sq ft of house space and 10 sq ft of run space for full size chickens as a guideline. I like having the recommended run space, predator proofed, so we don’t’ have to worry about letting them out early and for those times when we're gone. The hens are pretty self-sufficient for a couple of days and for longer trips a friend can check on them without having to come 2x every day to let them in and out. Most say to build bigger, we took this to heart and will probably be happy in coming years, though if I was starting over I’d consider going smaller. We’re zoned for 5. We built on an existing concrete pad and ended up with a coop sized for 7. Nice digs for our 3 girls who spend most of their time in the yard.

 

[Ridgerunner]

The difference between a draft and ventilation.

A draft is a breeze hitting them, especially on the roost. Think in terms of wind chill.

Ventilation is an exchange of good air for bad air.

With chickens you potentially have two different kinds of bad air. Wet poop can create ammonia as it decomposes. How much ammonia does poop create? That depends on how thick it is, how wet it is, and the temperature. Frozen poop will not create any ammonia. The warmer it is the more ammonia is created. Chickens respiratory systems are fairly sensitive to ammonia. They will die in lower concentrations that you would.

Ammonia is lighter than air. If there is a hole (ventilation) above their heads, the ammonia will not build up enough to hurt them. It will rise up and go out of the hole.

The other thing that can cause problems is moisture in the air. The higher the humidity in the coop, the more susceptible they are to frostbite. Many people on this forum have reported solving frostbite problems by increasing their ventilation. The moisture comes from their unfrozen poop and them breathing. You’ll never get your humidity below the outside humidity just with ventilation, but your goal should be to match that outside humidity. That’s the best you can do.

Warm air holds more moisture than cold air. Warm air rises. The chickens themselves generate some heat. In unusually cold weather the ground is likely a thermal mass and warmer than the air. If you have an elevated coop this doesn’t help air exchange. You’ll have to rely on the heat from the chickens. A hole (ventilation) above their heads will remove a lot of moisture. Two openings above their heads may cause a lot of air exchange and keep them out of the direct breeze between the two openings.

Each coop is different. We have different prevalent wind directions and different things blocking wind or tunneling the wind to the coop. I can’t tell you exactly what to do in your unique circumstances, but I’m a big believer in having lots of ventilation above their heads in the winter and lots of ventilation below them, level with them, and over their heads in the summer.

 

[Angaramiel]

Maybe I should state that we've only been inspired by the coop in the link, so please assume that we've already made all necessary changes to size, predator proofing, insulation, etc. We already have in the design enough ventilation over their heads, a vent on each side as well as an additional roof ventilator.
We were inspired by that coop because of the small footprint.
If someone has any experience with a ramp through the floor like that coop has, but in a colder climate, can you please tell me your experience? Would that hole in the floor cause airflow from that hole up through the coop itself and out through roof ventilation? (Assuming worst case scenario of windy with -10F overnight temps)
We're asking because it will change our plans of where to keep food/water in winter, maybe making for a larger footprint if needed.