Welcome to Just Answer. I will do my best to fully answer your question(s).
you can bring a small heater up on the roof and direct the heat into it may help. you will have the best success if you remove the melting water with a shop vac. Both the salt and hot water options will work eventually but I think the hotwater will work the best, XXXXX XXXXX the mess. If there happens to be a small crack in the freeze up the hot water wont take long to unthaw it. so the mess will be minimal.
The hot water idea that we were going to try involved hooking a garden hose up to our washer line and just letting it run into the pipe while overflowing onto the roof and onto the ground. Wouldn't there be a better way of doing it...or not?
One more than what else I already listed would be to purchase some heat tape and wrap as much of the pipe you can get your hands on. This will take awhile though. The tape is designed to keep it from freezing not thawing it out once frozen.
Yes there has apparently been alot of condensation that has built up and froze. the multiple turns definitely played a factor.
Just SLOWLY adding water to ALL drains to fill up traps is all that can be done sorry.
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Good luck to you on this.