New Roof to Avoid Leak

I am planning to replace the roof in this year. I want to know something about the features that I should look for in order to avoid water leak from ice-dam:
- I know that I should avoid low-pitch roof. I should improve the insulation in the top floor, and improve the ventilation in the attic. What other things that I should look out for?
- I am planning to have a gutter in the roof. But I am wondering what will happen if we have rain and the gutter is filled with ice and snow. Where will the water go to? Will the water go over the edge of the gutter and drop to the ground (this I think will be acceptable)? Will the water somehow go between the roof and the gutter and end up inside the house? Will I have to use one of those heating cable to melt the ice and snow from the gutter and the downsprout?
Thanks in advance for any input on this issue.
Jay Chan
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Jay Chan wrote:

You may want to call your city to find out what is required under local code in replacing a roof. For instance, the code may require applying ice dam barrier material to the roof before shingling. The barrier is a waterproof, adhesive-backed membrane that is rolled out and stuck to the roof deck. Local code where I live specifies that it must extend from the edge of the roof overhang to at least 3 feet up beyond the line where the exterior wall and roof meet.
This stuff doesn't cost a whole lot more than ordinary tar paper, but provides better protection against moisture incursion from ice dams.
HellT
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Thanks for the suggestion. I saw its use in several This Old House TV shows. I will definitely keep this in mind.
How's about the issue with gutter that is filled with snow and ice? Do you think using heating cable around gutter and downsprout is a good idea?
Jay Chan
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If you insulate the ceiling and ventilate the attic, then the roof will stay cold and there will not be any runoff water to ice up in the gutters. When the water melts on the roof, it will be above freezing anyway, so it will still not ice up. Well that's the theory anyway.
You may still want to put a membrane on the last few feet near the edge, to be on the safe side.

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This sounds reasonable. I guess I should replace the old roof with a higher pitch roof that has better insulation and ventilation, and with the membrane that you have recommended. And see what will happen.
If I still get leak caused by ice and snow in the gutter, I will put heating cables. Otherwise, I will not put them on the gutter, and save the money and the trouble.
Thanks.
Jay Chan
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There can be periods when melting can occur, not because of heat lost through the roof, but due to solar heating. Don't scrimp on the membrane it's easy to add more before you put shingles on.
I see many people putting heating cables in gutters. The run them up the down spout and along the inside of the gutter. I prefer not to do it but it seems to work.
RB
jstp wrote:

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If solar heating is happening, the conditions will continue to exist for the water to keep being liquid instead of frozen. Plain and simple, any heat that gets into the attic needs to be gone before it can heat the roof from the underside. Peak venting and plenty of soffit openings, unobstructed by insulation. That's the ticket.

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