Do a Google search for "reducing condensation in buildings" and some nearly universal causes and solutions will materialize. This is one example, but the Internet has tons of information just like it:
https://www.designingbuildings.co.uk/wiki/Condensation_in_buildings
Bottom line is they will all say to reduce moisture in the buildings, solution is to a), reduce moisture generated in the building, b) provide heat to allow air to hold more moisture, which is felt as a lower relative humidity and c), increase ventilation to move moisture laden air to the outside.
Most of us see this all the time in our bathrooms. Take a long hot shower with the door closed and the vent fan off and you will step out into a warm, sauna like room, with moisture condensing on everything in sight. Mirrors fogged up, windows fogged up, and just about anything metal dripping wet. But turn off the hot water, open the door, turn on the vent fan or do both and all that will instantly go away. Temp will drop, but all the fog and condensation will go away and the room will start to dry out.
Basic condition is that in any building where air and moisture can move freely back and forth, such as an open sided shed, temp and relative humidity levels will tend to be the same, inside and out. Even closed up, the laws of physics suggest that pressure, heat and moisture levels will try to equalize, only slowed by any barriers that are in place (closed doors, closed windows, vapor barriers, insulation, etc). Managing the movement of heat and moisture is huge issue in virtually all buildings that make an attempt at some form of environmental control.
Think of a chicken house as being like a bathroom. Once we populate a building with birds, things are no longer the same inside and out. The birds themselves are the source of two things......heat and moisture, both of which are going to move to the outside.
So if we could just add heat from the birds or another source, the ability of the warmer air to hold more moisture goes up and the relative humidity level goes down, leading to evaporation of moisture from any wet surfaces. One free and easy way of doing this is in winter is to include lots of window space on south facing walls to allow sunshine to stream in resulting in heat gain from solar radiation. This even helps during the day when the birds are out and about and not in the building. If the house interior heats up any at all relative to the outside temps, it starts drying out. So windows not only add beneficial winter light, but also heat. But they need to face south into the winter sun to allow this to happen.
But in addition to the radiant heat given off by the birds, they also bring in moisture. From their breath, from their droppings and if we have waterers, etc. inside the coop, any spilt water has to evaporate. Also, if the coop has a dirt floor and moisture is being drawn up from the soil, that goes in the air too. These are all sources of water that if not vented, or if enough heat is not added to allow the air to hold it all, will build to the saturation point and start to condense out. In the extreme, moisture will condense on just about everything, including on the birds, will then evaporate from the heat generated by the birds, leading to that cooling effect. They are being chilled. This is really felt at night, when the air is cooling. The cooling effect, taken to the extreme is what causes frostbite. Do a google search on "causes of frostbite in chickens" and almost all of them will make some sort of reference to excessive moisture in the building, combined with zero or sub zero temps. So somewhere around 0F is where the bird's natural ability to ward off frostbite fails. A dry bird can go below that. A wet bird will likely suffer some damage.
So to house birds in zero to sub zero temps, without the need for supplemental heat, two things need to happen. Any heat from the birds and/or solar gain from sunshine streaming in through windows will lower the relative humidity level to help avoid condensation, but the moisture being generated by the birds and other sources is still building. If that moisture is not vented, as soon as the air cools just a little bit, humidity level goes to 100%, the dew point is hit and moisture starts to condense. Think wet bathroom. So there needs to be a controlled level of put and take. A controlled level of warm moist air moving out as it naturally wants to do and being replaced by cooler make up air, which when warmed just a little bit takes up the moisture being generated by the various sources found within the house. In short, a conveyor is setup moving the moisture out but at a controlled rate such that the heat level always stays above the outside temp. That elevated temp is the engine that runs the conveyor. A bathroom vent fan does about the same thing if you run it while taking a hot shower.
In cold climates, (my guess is this kicks in around Zone 6a), insulation is needed in the walls and roof to help hold in the radiant heat generated by the birds to get that 10 to 15 degree temp spike of inside air over that on the outside. Without insulation in sub zero weather, the bare walls will suck the radiant heat out and in turn, radiate it to the outside vs. convection of the warm moist air to the outside. In short, in Zone 5a and colder climates, insulation is likely needed to help keep the conveyor running. We are hearing reports of birds kept in unheated houses down to -20F and colder, but temps inside these houses are about 0F and warmer and no frostbite.
Seriously tricky business getting ventilation right in cold weather climates!
Note: I edited this post to reflect a change from zone 5a to 6a as the threshold area where a person might want to consider adding insulation. I live in zone 6a and we have already been down below zero about 3 or 4 nights.......and we were hearing reports of frostbite from others living in similar areas at the same temps. Some tight houses with high bird populations seeing frostbite at low single digit F temps. Still, that is only a few nights a year, if that. Or, it may go to -10F or worse a few times, even in zone 6a. On the other hand, zones 5a and colder may see those levels 20 or 30 times over the course of a typical winter. So zone 6a is the threshold to consider it, but probably not needed. Zones 5a and colder probably should include insulation in their build. Goal or purpose of insulation in these houses is to reduce condensation on interior walls, and to reflect radiant heat given off by the birds back into the coop vs. letting it be absorbed by the uninsulated walls to radiate out into the cold. Radiant heat trapped in the coop may be enough to raise the temp inside the coop as much as 10 to 20 degrees F over the outside them, and that is enough to bump a -20F outside temp to 0F, and lower the relative humidity level inside the coop in the process, staving off condensation and drying the house out, and thus reducing the chance of frostbite. 
