I have ice damming in my present home, during any bad winter...where we get heavy snow fall in short periods of time.
The primary reason for this is migration of heat escaping from the building through to the roof where the snow slowly melts and then re-freezes close to the eaves (where there generally is less insulation and colder roof surface).
I have used heat tapes (which work good, but require electricity).
I have used ventilation fans which take in colder outside air to equalize the attic space to outside air temperature (did not work well, and is an energy waster)....and I have to rake the roof off during bad snow accumulation.
Unfortunately some places its hard not to have this ice damming.
Built up roofs are probably the best roofs to have in these climates....so my next place is going to be a built up roof.
I am never going to build another Gambrel roof in Maine.
They also sell chemical ice melting hocky pucks, or some people use the ice melter pellets and put them in a panty hose or stocking and put them on their roofs to slowly melt the ice dams when they occur....however the chemicals can sometimes be damaging to shingles (especially metals) and vegetation.
In many of the northern or colder climates, low voltage heat strips are used along the lower 3' of eave overhangs. Additional snow guards are also used to break up sliding snow. These do help, but large snowfalls, or several freeze/thaw cycles can produce a sliding "mass" that will rip both away on occasion. Especially challenging in your large valley systems.
Yeah.....like last winter.....several snows of 18 + ".
My snow just sits there for days...no sunlight either...and slowly melts.
Several hundred pound chunks.
I had a friend in Houlton who lost his entire porch roof several years ago, when he was beating the ice dams with a maul / sledge (common practice) and a huge dam broke free and crushed the porch roof.
He was very lucky.
If it was me....I would just eat the cost of traditional heat tape (I didn't know they had low voltage ones maybe they are just as good?....hmmmm interesting). I used to put mine on both a timer and had an on and off switch for really bad accumulations, and it worked great on my asphalt roof.
However when I went to the metal shingle roof...no more heat tape.
The problem is simple. You do not have enough insulation in your roof and you do not have adequate roof venting. If you want to fix it once and do it right you need to remove the roof and add a lot of insulation. Then ensure that it has good venting. Do that and it will not be a problem again.
Khita Log Builders Ltd.