We live in the Salt Lake Valley in Utah. The lows are typically in the 20s with the few days in the teens. Would the chickens get too cold in that much space?
Is the shed insulated? My 8×10 has insulated walls and 2" foam panels in the trusses. Allows for ventilation in the peaks, and has 3 windows. Solar fan to help draw out excess heat on hot days.
When I was designing and building my chicken coop, I thought I too would need an insulated coop for my cold northern Minnesota winters where we get -40F in the dead of the season. But, none of the typical chicken owners around here have insulated coops because why do you need an insulated building if you are going to have windows thrown wide open for ventilation? Insulated or not, your inside coop temp and humidity should be almost the exact same as the outside temp and humidity if your ventilation is adequate. If your coop humidity is higher than outside, then you probably have a ventilation problem that could lead to more frostbite problems. Someone told me that the difference should +/- 3% if ventilation is adequate.
I do know of one breeder that has a climate-controlled chicken coop, with an insulated building, and he runs heat and AC as required to maintain about 72F year round. That is because he is breeding show birds year-round. He told me that it costs him a lot of money to have a climate-controlled environment for his show birds, but he sells them commercially and it's just a cost of business for him. He advised me not to think about insulating my coop because, normally, it would not be money well spent. Like everyone else, he said ventilation is key and you can't control the outside temp or humidity, so you only need a coop that is basically draft free.
I don't think OP will need any kind of insulation for their coop in Utah in the winter. The chickens maintain a body heat of 105F, and they can trap air in their feathers to keep warm even in my cold -40F nights here in Minnesota. Just have to make sure that no draft is coming up from underneath the birds while sleeping on their roost bar.
Relating to a cold weather link in a previous response, I respectfully disagree with the notion that you need to keep your water outside the coop. I keep my feed and waterer inside the coop 24/7/365. In the winter, I have a metal base heater to keep my metal waterer fount from freezing. Although it is only rated to keep the water from freezing down to 10F, inside the coop it has been able to keep the water from freezing even down to -40F. I suspect that is because there is no wind blowing over the water inside the coop.
Also, I was concerned that heated water might raise the humidity inside the coop. But, according to my inside and outside weather sensors, my temp and humidity inside the coop was the essentially the same as outside the coop. So, I just stopped worrying about heated water causing a frostbite issue inside the coop. Of course, this may be related to the size of my coop and the number of chickens in it. I have almost 8 square feet per bird in the coop and I have a Gambrel roof with the peak maybe 9 feet high. Lots of room in my coop for my flock similar to what OP has.