The reason you need gutter cables is because your attic is not insulated and ventilated properly.

What happens is that heat rises in the attic, and the snow on the peak of the roof melts, and the water runs down the roof. As the water nears the edge of the roof it freezes (the roof temperature is lower - since there's not as much attic space under it).

The real fix is to make sure you have proper vents in the soffit, roof, and proper insulation in the attic.

That way the snow on the roof won't melt, and you won't have ice cicles.

Hi,

the is definitely not good for a snowy roof. It does not rise in the attic but it is rather produced in the attic in my case. Soffit venting ? Hmm.. I am not even sure I have such thing beneath the roof.
Anyway, even under these circumstances, I still think that the defrost cable should have melted the sliding roof snow faster. Or not ?

The purpose of the gutter cable is to prevent ice daming. This occurs when the water in the gutter freezes and pushes the ice up the edge of the roof. The ice causes the roof shingles to lift up allowing water to penetrate the roof.

The gutter cable needs to provide enough heat to melt the ice along the edge of the roof and in the gutter. If that is occurring then the system is working. The gutter cable is not supposed to melt the icicles hanging on the gutters.

Are you able to watch the water flowing down from the gutters when the cable is on? If not then you may need to add another cable.

@mike home: "The purpose of the gutter cable is to prevent ice daming. This occurs when the water in the gutter freezes and pushes the ice up the edge of the roof. The ice causes the roof shingles to lift up allowing water to penetrate the roof. "

Where does the water in the gutter come from? It comes from the snow melting off the roof. Make the roof colder, and you won't have any water.

Check out these images:

http://www.google.com/imgres?imgurl=http://www.massenergylab.com/blog/wp-content/uploads/2012/03/wind-washing.jpg&imgrefurl=http://www.massenergylab.com/blog/?p%3D1657&h=480&w=576&sz=113&tbnid=EPVy840-qD1GBM:&tbnh=102&tbnw=122&zoom=1&usg=__Dg-DRaoUPY1IYGSMkQc2P1600qo=&docid=ckkz7b8qhaB6LM&sa=X&ei=QyTwUPn-HNL4rAG1oIGwCQ&ved=0CEgQ9QEwAw&dur=0

http://www.google.com/imgres?imgurl=http://spinspect.com/blog/wp-content/uploads/2010/01/WindWash1.png&imgrefurl=http://spinspect.com/blog/?p%3D110&h=364&w=556&sz=57&tbnid=Le-6xmcrIHvReM:&tbnh=91&tbnw=139&zoom=1&usg=__wfbIe_pRROqtNfyYN2emyR3I7VQ=&docid=eXePEmAJUH7HEM&sa=X&ei=QyTwUPn-HNL4rAG1oIGwCQ&ved=0CEsQ9QEwBA&dur=719

Thank you both.
So, what I get from here is that these heat cables won't prevent the forming of and won't melt icicles. They just prevent icedams (meaning roof damage and facade leakage). Which means I got the wrong medicine for my problem in the first place.

What I should have done was to ensure some airflow through the attic (soffit vent) so I could stop heat spots / areas in the roof. Well that leaves me with other 2 questions:

1. If I was to have those vents then it would imply some heavy insulation just like in the pictures above from doug's links; but if I had such heavy insulation then why the need for airing ? insulation = heat stays inside.

2. With or without insulation, temperatures are pretty whimsy here. For a week they go above zero, for the next week they go below zero. It would be the same situation - snow melting, flowing over the eave's brim and forming icicles which would freeze the next week, grow some more the week after, and so on :/

@kelogs: "1. If I was to have those vents then it would imply some heavy insulation just like in the pictures above from doug's links; but if I had such heavy insulation then why the need for airing ? insulation = heat stays inside. "

Some heat will leak into the attic, and especially on a sunny day the roof will absorb radiant energy - and heat the attic.

The soffit vents and the roof vents (near the peak allow the warm air to rise and escape). If there's no soffit vent, the warm air would be trapped in the attic. The ideal situation is to have your attic below freezing.

I live in Minneapoils, where it's 5 degrees right now. I don't have any icicles or heating tape. Get someone to install a few soffit vents and maybe beef up the insulation - especially at the top plate of the wall.

doug_gb,

I agree with you adding more insulation in order to keep the attic cold will help prevent ice daming. But is it enough? What happens if you have a roof with dark shingle with sun on the south side of the peak, and ice on the north side. Won't the attic warm up and cause the ice to melt. At night the ice will freeze when the temperature drops below freezing. I assume the wind washing technique your links demonstrate will help minimize the case I described.

Kelogs,

The attic collects all the moisture from the house. You need air ventilation in order for the moisture to escape. If there is poor ventilation you will eventually have problems with mold.

You should also verify the gutters are pitched properly so they can drain the water. Sometimes gutters will develop a low spot. The slope in the gutter is need to allow the water to travel to the down spout.