Your attic doesn't have enough ventilation to the outside.
I agree. Warm air is reaching the singles one way or the other. "Renovation" seldom tackles an inadequate rafter design.
He said he has not had any previous issue with his roof. I'm not going to speculate.
Shows up some pics of your current rafter ventilation Slybry. 
Railton
Sheesh. He didn't have any issues HE WAS AWARE OF. Combination probably of warm water hitting the cold air/steel and since the gutters now have shielding on them, the water is probably freezing on top of the shielding rather than inside the troughs which in all probability it was doing before and not visible.
From experience, the best kind of gutter screening/guards are the ones that look like a grate in a diamond pattern and are made out of metal (usually aluminum), they still allow the little stuff through but also provide plenty of drainage and stop the big stuff from getting in.
Once the spring comes and the ice melts, have a look where the eave troughs connect to the fascia and look for signs of water damage / staining. The best way to find the solution is the process of elimination.
As Railton says though.... we need to see pictures to determine what the slope of your roof is etc.....
The last few winters we've had were mild.... maybe that's why it wasn't noticed. I dunno.
