It depends on some things, age, type etc.
Each season here my figs are stored in attached garage no heat ever.
Each season temps get in the teens for several weeks mostly January, in 2008-2009 winter season lowest garage temp was 6 - 8 F and outdoors was -23F. Youngest tree if memory serves me correct was 2 to 3 seasons old and when temps got that cold inside garage i threw bed sheets over them.
No Damage in spring but if very young plants first season ones i believe may have had damage or died that year in my garage.
Martin

I agree with Martin. It really depends on the fig cultivar and the age of the tree. I got 72 gallon size and 10 3 gallon "prize" little trees inside my garage. My garage is insulated but not heated. Here in my area (Charlotte) we will get temps down to 15 degrees but only 25 inside my garage. And I got about 90 or 100 inside my little greenhouse. Those in my greenhouse are older and can tolerate temps down to 25 degrees but I am just using my GH to keep them from getting below 25. I also have about 30 outside sitting tight against my house wall creating a microclimate. These trees are 2 and 3 years old and come spring I will plant them in the ground. Dennis