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Heat from stovepipe turns snow on metal roof to ice. Ice removes chimney from roof.

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Bear's Nest, Feb 18, 2013.

  1. Bear's Nest

    Bear's Nest New Member

    Joined:
    Feb 18, 2013
    Messages:
    1
    I have an old Centennial wood stove on the second floor of my house. At the ceiling, the black stove pipe goes through a collar and the stove pipe turns into double wall stainless steel. On the third floor the s/s stove pipe is enclosed in an uninsulated drywall and stud chase. The stove pipe then enters the attic. There is no collar preventing air from the pipe chase from entering the attic. There is only about a foot or two of stove pipe in the attic because the third floor has a cathedral ceiling and the chimney is located near the eave. The s/s stove pipe emerges through an exposed-screw steel roof. The steel roof sits on 1X4" pearlings which sit on half-inch plywood decking. The attic is well insulated. The roof has a 6 and 12 pitch. The attic has ridge vent, sofit vent and gable vents.
    When we use the wood stove in winter, it heats the attic and steel roof. This melts the snow, turning it to ice. When the weather warms, we get tons of ice sliding off the roof and bashing dents in a porch roof down on the first floor. These slabs of ice take the chimney with them. I tried using a snow diverter, but the ice took it too. (I have patched the hole in the roof where the chimney came out and if I were to give it one more try with the snow diverter, I'd use bolts instead of wood screws to hold it in place.)
    I've looked into installing snow breaks on the roof to keep it from sliding. Last year we had a record snowfall which would have needed shoveling if we didn't have a self shedding steel roof. I'm not crazy about shoveling a 6 and 12 steel roof which is 30 feet off the ground. When we don't use the wood stove the snow slides off the roof more or less as snow which does not damage the porch below. It just fills our yards with snow berms. (The ice could easily kill someone if they were standing there when the ice comes crashing down.)
    My ideal solution would be to move the stove to the center of the houses so that it exits the roof near the ridge. I might also move the stove to the first floor to better heat the house. It seems to me that the drywall and stud pipe chase should be sealed at the attic to prevent heat loss. I heard that this would be against code. In winter, the existing drywall pipe chase wall is cold and moisture condenses on it because cold air from the attic is allowed to to come down the case. At the least, I think the drywall should be insulated. While you're at it, why not build an insulated pipe chase around the double wall stove pipe in the attic to prevent heat from entering the attic. I guess the contractor who put the steel roof on wanted to keep it cooler by putting the steel panels on 1X4 pearlings--thus allowing cold airflow between the steel panels and the plywood decking. This would work if it were not possible for heat from the pipe chase to enter this 3/4 inch gap and be distributed over half the roof. If I were to leave the stove where it is now, I should at least spray a foam seal in a circle around the hole where the stove pipe comes through the roof. The foam would go between the steel roofing and the plywood decking.
    Does anyone have any suggestions on how to fix this bad design problem?

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  2. ddahlgren

    ddahlgren Feeling the Heat

    Joined:
    Apr 18, 2011
    Messages:
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    Loc:
    SE CT
    If having a fitting between the ceiling and attic against code why would dura vent include one with their install kit for duravent plus?
    See the attic insulation guard here
    http://www.duravent.com/Product.aspx?hProduct=2
    The fitting goes through the ceiling and then has a sealing collar that goes on top of it. Anything that lets room air into the attic is a very poor idea. I would ask you said it was against code where they have a citing of it in print.
  3. Lumber-Jack

    Lumber-Jack Minister of Fire

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    Beautiful British Columbia
    Snow melting and refreezing on a roof is common whether you have hot air leaking into your attic or not, you are basically dealing with 3 different issues.
    The first being the air leaking into your attic, from a purely energy conservation point of view I would want to find a solution to that, it doesn't seem right.
    Second is your chimney getting torn off by the ice. I know ice forming on the roof can cause all kinds of problems. I also have a metal roof and have had my share of problems dealing with it. I lost a plumbing vent this winter that I'll probably have to fix this spring. Fortunately my stove pipe is located closer to the peak of the roof, so I don't get enough snow accumulation above it to be a problem. You suggested moving your stove and flue, if that is feasible it might be the best solution, but I'm surprised you ice diverter didn't work, you don't have any pictures of it do you?
    Your third problem is dealing with the snow and ice on your roof in general, which is something I've still dealing with. As I said I lost a plumbing vent this winter because of the excess snow accumulation we had this year. It was on the opposite side of my wood stove and a different part of the roof, so it had nothing to do with heat from flue causing ice to form. In fact the roof is insulated pretty well, but ice can still form even on roofs that have no heating at all below.
    The ice and snow accumulating on metal roofs can be a serious problem, as you mention it could come down and kill somebody if it happened at the wrong moment. I personally make a lot of effort to clear my roof of all the snow after we get a big dump. I'm torn between installing ice dams or not, on one hand it would stop the snow (and ice) from coming down unexpectedly and killing someone. On the other hand once the snow slides off the roof I don't have to worry about it any more, and if I was to install ice dams it would hold the snow up there till spring and every time we get a bit of a melt it would start to drip and refreeze, and that causes it's own problems, plus ice dams tend to catch all sorts of other stuff like leaves and so forth, so they need to be cleaned periodicity. Having a very steep roof the prospect of getting up there and cleaning out my ice dams doesn't seem very appealing.

    Decisions?
  4. Lumber-Jack

    Lumber-Jack Minister of Fire

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    How did you patch the hole in your roof?
  5. DAKSY

    DAKSY Patriot Guard Rider Staff Member

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    I would run aluminum sheet formed into a box, 2" clear to all sides, that runs from the top of your ceiling joists to the bottom of your roof sheathing. That would essentially become an elongated attic insulation shield & I can see no reason for a fire of building inspector to red ink that sort of fabrication. That should contain the heat to the immediate vicinity of the flashing. With 84" out of the roof, didn't you also have a roof brace kit?
    tfdchief likes this.
  6. webby3650

    webby3650 Master of Fire

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    I'm not sure why this would be against code? You should have firestops/draftstops installed at ceiling height.
    You are pumping heat out of your house big time! Does it have any firestops in the chase?
  7. Bret Chase

    Bret Chase Minister of Fire

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    this falls under damned if you do... damned if you don't... a Class A will get above 32F while it's being fired....above 32 melts snow and makes ice..

    They're not "pearlings"... the 1X4's are there to protect the roof deck from the solar gain of the roof panels... not unlike a metal heat shield w/ airgap behind a stove. Purlins are structural members that carry the load between king rafters... think Post & beam.

    The chimney being "cleaned off" is definitely not a good thing... you could try to pack the joint between the living space and the attic with rockwool... the only way you're going to fix it is to put snobar above the chimney... 1 bar per 5'...

    I have installed literally acres of metal roofs... each and every owner never believes me when I tell them of the power of the shedding roof....
  8. webby3650

    webby3650 Master of Fire

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    Last month, I went back to a recent job to replace the storm collar. Sliding ice ripped the storm collar off and dented the flashing. The flashing will be just fine fortunately. It's amazing how destructive it can be!

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