I’ve stayed in Yurts like this in the Sawtooth range of Idaho in February with night time temps of -10F. They fare well when there is a wood fire going, and better if there is a solar/battery ceiling fan to circulate the rising warm air.

In the summer direct sunlight can warm them considerably, but if well placed in shaded areas then the temperature is well moderated. Some units have a vent in the oculus at the top for use in the summer.

There is zero mildew if platformed well and clad properly with water protective barriers.

Ironically, traditional yurts very similar to these are used in places that go from -40C to +40C throughout the year (Mongolia, Tuva... though true, when it’s -40C, hopefully you’ve packed up your yurt and moved it down the valley to the winter grazing location that’s a little less harsh...).