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d3500ram's avatar
d3500ram
Explorer III
Sep 22, 2015

Installing roof snow/ de-icing heat cables on roof...?

I am going to install roof snow/ de-icing heat cables on a portion of roof that is prone to ice damming. The repeating WWWWW pattern at the eave overhang makes sense, but what about the valley?

I have a 4/12 pitch, 6'-0 on one side and 20'-0" on the other with the valley rising about 23'-0" to the ridge.

I want to run the heat trace up the valley- should I do a criss-cross pattern similar to the WWWWW but running it up the valley or can I do 4 straight runs parallel to the valley (2 on each side.)

I am leaning towards the straight run pattern because it will be an easier install. I cannot have the cables overlap; if I do a criss-cross I would have to do the pattern up one side of the valley and the same on the other side to bring the cables down... lot of clips and spacers needed for that.

Thoughts?
  • westend's avatar
    westend
    Explorer
    Sep 22, 2015
    eHoefler wrote:
    You should run the w pattern. The purpose of the w, is to have a melted channel from the leading to the low point. Running parallel in the valley does not make a path into the valley. You may have a clear path in the valley, but you would have no path to the valley.
    True, but the objective is to prevent ice-damming so melting snow back two feet on either side of the valley is not needed.

    I do some heat cable installation for ice damming and there is not a whole lot of need to heat an entire valley unless the valley is a source of water intrusion. I typically just make a double run up the valley until it is past the overhang area (usually 3' or so). If I am using the cables on all the overhangs, the valley run can be part of the overall cable run. BTW, don't forget the downspouts. Depending on ambient temps, the downspouts may freeze solid if not heated. That is typical in Winter up here.
  • eHoefler's avatar
    eHoefler
    Explorer II
    Sep 22, 2015
    You should run the w pattern. The purpose of the w, is to have a melted channel from the leading to the low point. Running parallel in the valley does not make a path into the valley. You may have a clear path in the valley, but you would have no path to the valley.
  • JaxDad's avatar
    JaxDad
    Explorer III
    Sep 22, 2015
    The zig-zag pattern is to cover a wider area along the eaves. That is not required for a valey. Bear in mind though you need to to place the retainer clips onto shingles, that might be an issue with a metal valley. I ran mine up one edge of the shingles, across the valley, and down the other shingle edge.

    It's worked well so far.
  • d3500ram's avatar
    d3500ram
    Explorer III
    Sep 22, 2015
    Thanks Dennis, that is my same thought too... appreciate the confirmation. I would have to do at least 2 runs in the valley, one to go up and another to come back down to continue to the other eave.
  • Dennis_M_M's avatar
    Dennis_M_M
    Explorer
    Sep 22, 2015
    Just one strip up the valley lengthwise should be sufficient. The purpose of the cables is just to keep a channel open so water flows of instead of building up behind a dam. I've done several houses and just enough cable to form the channels does the trick. More than that is a waste of time and money.

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