Great report!
My experience was similar, except our temps were only to -10F. Although my freeze proof hydrant is currently "frozen".....or at least not working. Holding my breath to see what happens when the frost goes out of the ground. Point being that has never happened before, so our temps may have been lower than -10F.
Anyway, this is what we had two weeks ago.......
View attachment 1660545
A few days after this was taken, wind was blowing 30 mph from the direction the photo was taken. Right into the open front. Birds by the window had their feathers ruffling, but the wind movement only penetrated to the scratch shed......back part where the roosts are was dead calm.
BTW, this one is 8' x 12'. Good for up to 24 birds. The 23 in there now stayed in for a week with no issues. A dozen birds in this could ride out a long nasty spell of winter with no concerns.