Welcome to BYC.
I have to clock in to work in a minute so I only have time for a little quick copy-and-paste that may or may not be directly relevant.
I'm sure others will chime in.
First, define "cold" -- what are your summer maximums and winter minimums? And are you wet or dry?
The Usual Guidelines
For each adult, standard-sized hen you need:
- 4 square feet in the coop (.37 square meters)
- 10 square feet in the run (.93 square meters),
- 1 linear foot of roost (.3 meters),
- 1/4 of a nest box,
- And 1 square foot (.09 square meters) of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost.
How to Provide Good Ventilation
There are many ways to provide ventilation in a chicken coop and the ordinary windows that are so often seen on coops, especially those designed to have strong visual appeal, are often not the best choice. As noted in the Usual Guidelines, ventilation is best placed above the chickens' heads when they're sitting on the roost. This is both because heat and ammonia rise and need to escape at the top of the coop and because such ventilation is draft-free.
Wait a minute, what does "draft-free" actually mean?
It doesn't mean total lack of air movement, it means no strong breezes capable of ruffling the birds' feathers and thus disturbing their down-parka insulation. Look at my run-into-brooder conversion:
https://www.backyardchickens.com/articles/run-to-outdoor-brooder-conversion.76634/
That's an 8" opening all around the top -- 16 square feet of that permanent, 24/7/365 ventilation we talk about. Even with all the vents open on both ends it's draft-free for little chicks because of the cardboard barrier. Soon that barrier won't be necessary and for adult birds in a warm climate it would never be necessary to pin down the tarps except in blowing rain.
Vents at the top of the wall are easy to make as long as you plan generous roof overhangs. Just don't carry the siding all the way up and cover the gap with hardware cloth. If it's a sloped roof rather than a flat roof be sure to put the vents on the walls at the bottom and top of the slope so that you get a constant flow of air on the underside of the roof to carry the heat, moisture, and ammonia away.
If you're building a peaked roof then plan on leaving out the soffit blocks and either installing a ridge vent, gable vents, or both. Remember that ridge vents are easily blocked by snow and that ventilation is just as important in the winter as in the summer. (See
this article on cold weather chicken-keeping).
Monitor roofs and cupolas are traditional means of providing for top-level ventilation that is both draft-free and weatherproof. With sufficient roof overhang they will continue to work despite moderate snowfall (and if your snow is deep enough on the roof to block them you might want to be clearing the roof to protect the structure anyway). The coop page for my
Little Monitor Coop includes construction details for framing a monitor,
this coop includes a functional cupola, and
here you can see how another BYC member mounted a monitor on the roof of a plastic shed.
Top hinged windows are the best windows for providing supplemental ventilation at a lower level because they act as their own awning to protect against rain and can be adjusted to account for different temperatures and weather conditions. Here's
one way to make a safe, adjustable prop to keep them open. Sometimes it's good to have a window down low to allow cool air to enter at or near ground level. The top hinge concept works for this too. Since I never need to close mine in this climate I just tucked it under the roof of the nest box.
Remembering that chickens don't stack for storage and thus height can't compensate for lack of floor space, height is your friend when it comes to ventilation. When trying to add ventilation to an existing structure, if the roof is high enough above the roosts you can pull the siding off the gable triangles or open up the soffits and/or the top of the wall. Roof overhangs are also your friends.
Yes, sometimes when you have a very small coop, especially a commercially-made coop, you will realize that getting adequate ventilation means
replacing an entire wall with wire. That's one of the reasons why BYC regulars usually advise against using those small, commercial coops -- they are dreadfully hard to ventilate properly. In some circumstances, especially in warm climates, pulling off the wall that faces into the roofed run
actually is the right way to solve the ventilation problem.
Adding roof extensions to shelter these vents can be intimidating to inexperienced handymen. Here's how-to (and how not to), extend a roof by sistering the extension to the rafters:
https://strousehomeinspections.com/blog/structural-roof-extensions.html
And here is how to use lookouts to extend the roof at right-angles to the rafters:
https://www.backyardchickens.com/ar...e-overhangs-eaves-of-a-shed-coop-house.76599/
This member did a nicer job putting awnings up than I did on my brooder:
https://www.backyardchickens.com/threads/check-out-my-chicken-tractor.1456418/post-24496139
