Originally Posted by vehve
Bruce, the ice does get heavier due to condensation when the warmer weather sets in. Warmer air carries more humidity that sticks to the ice. But most roofs should be able to hold that weight.
True but more humid air adding a bit to the ice/snow on the roof isn't any different than new snow falling. Plus the ice/snow is also ablating in very cold weather or outright melting on sunny days (which are more frequent in cold weather) so unless you are under a constant snowfall, the load is typically limited in quantity (*). It is 24F and sunny today (10.25 kWh as of 1:30 PM ) and all the snow that was on the roofs has melted or slid off except a wee bit near the rails themselves. I don't have rails on the older building since I'm NOT sure if I can trust that roof. Same construction but prior owner did a lot of shimming and put metal sheet roofing on that (if done the same as the rebuilt building, leaving the old asphalt shingles on). I wouldn't trust that stuff to hold rail and I wouldn't want to screw through the metal to the decking (however far below it might be in a specific location). The deck under that roof is a lot wider though so whatever falls isn't going to take out railing. Whenever we replace that roof, it will be with standing seam and I will put rails on it.
If we got totally dumped on like more southern and eastern parts of New England last winter (my BIL south of Nashua NH had 5' in his yard), I would consider using the snow rake to pull some off. There IS only so much any given roof can hold.
* past performance does not guarantee future results!