When I tried googling this question, I found the answers for "What is the lowest survivable body temperature" and "humans can survive for a few minutes in -200 degree weather". Neither of which are my question.
I've read that the internal temperature of igloos can be in the wide range between 19 F and 61 F (-7 C and 16 C). 61 degrees I could see being reasonable, but 19 degrees seems nearing too cold for survival. I'm wondering where that cutoff point is. What is the lowest temperature that living in it continuously (say, a week or more) poses a serious health risk?