Theres a chart floating around that has freezing temps of beer by alcohol percentage.
If the temps were in the 20's outside and it stayed at 40 in the garage than it makes sense that if its in the teens you wont be below freezing in the garage.
Not sure how a garage stays 15 degs warmer than outside temps in an unheated garage
Couple of factors might help. Insulation and being out of the wind. On an icy day, you expose a water pipe to wind, a hole in the outer wall perhaps, then it will freeze. If you simply plugthe hole, you greatly reduce if not avoid any freezing. Most garages will have some minimal insulation, including some in the door, as well as some latent heat, if attached to the house.
I live in Canada. I have a detached garage that is pretty "porous" at the end of the day. If it is minus 10 C outside, i'd still seek refuge from wind and weather inside the garage. Simply being out of the wind helps. Now it gets cold in my garage, but I am willing to bet that it is still 5 degrees warmer than outside. If it was attached to the house.... then I'd expect it would be almost habitable. Certainly not able to freeze water over a week or two.
I have a non insulated porch in my basement apt that gets to around 40 degrees. It may vary 4-5 degrees depending on the weather outside, even dip below 40, but I'd be very surprised that my beer ever froze, even with outside temps well below zero. I have a cider out there now, that was essentially yellow, when I dumped it out there 3-4 days ago. It's already turning a nice orange and visibly clearing.
My question is how cold does it really needed be for bring the yeast out of suspension (if that is the correct term)? I could probably walk my pale to my garage about 15 yards and attain almost freezing temps, but is this any better than my 40 degrees? I am chiefly concerned about dropping the bloody thing, then all the further agitation from simply carrying it any distance at all, and defeating the actual purpose.
I would then want to transport it back, to bottle inside, as I am not flash enough to have a keg operation. All more. movement that I fear could agitate the cake/trub even after a crash.