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Icecicles and ice dams

Post in 'DIY and General non-hearth advice' started by fabguy01, Dec 12, 2008.

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  1. fabguy01

    fabguy01 New Member

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    I seem to have a problem with ice daming up on the eve's of our house, It is a 1300 sq foot ranch with a hip style roof that has about a 18" of blown celluose insulation. When insulated care was taken not to blow it into the eve's. this year I tried adding additional vents into the soffits but it diddent seem to help. anyone have any suggestions? Thanks Nate

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  2. Gooserider

    Gooserider Mod Emeritus

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    I don't have anything specific, but this has been discussed fairly often in the past. If you haven't tried it yet, I'd try doing a forum search on "ice dam"

    Gooserider
  3. Tudorman

    Tudorman New Member

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    1. Check if the insulation around the perimeter of the attic is up against the underside of the roof. There should be at least a 1" gap between sheathing and the insulation to allow the cold air into the attic space.

    2. Since you have a hip roof, venting the ridge usually requires roof vents since the ridge is short or non-existent. do you have any? I forget what the recommended free area is for the venting, but it ought to be easy to find on the 'net. Or call your local building department to see what code requirement is on new construction.

    3. What's the R-value of your attic insulation now? It should be at least R-30, and more is better. You want that roof COLD.

    4. Check for air leaks and gaps around anything that penetrates the attic space. Access scuttles, ceiling fixtures, recessed lights, plumbing, HVAC ducts, anything. Does your chimney or stove vent go through the attic? That could be a problem. Seal the gaps and insulate. Just be careful if your chimney or vent is there. Don't create a fire hazard.

    Good luck.
  4. fabguy01

    fabguy01 New Member

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    Thanks for the info i think you might be right with the ridge vent idea ,I can look around the perimeter of the roof i can see daylight and about 2 1/2" air gap between insulation and sheathing,No ridge vents, r-value is unknown but it has blown in insulation that covers the 2x6's and 8" rolled fiberglass on top, i have a OWB and a insert with a brick chimney however i amm only osing the OWB at this time so i dont think that the chimeney would have an effect ,would it? Everything seems to be pretty well packed around pipes and such but what about my hot water vent ?is there a way to insulate it? I was thinkig about installing a power vent with a t-stat or one of those spinning ball vent thingies<sorry dont know the real name. thanks in advance Nate
  5. PaulRicklefs

    PaulRicklefs New Member

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  6. oconnor

    oconnor Minister of Fire

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    The bottom line is your attic temp needs to be the same temp as the outside air. If you are getting ice damming, figure out how the heat is melting the water, and stop the heat.

    Ventilation in attics is quite overrated - it is needed to keep the moisture content in the attic down, but the easiest way to stop the moisture is to stop the moist air from entering, and most of the moisture comes from the house. Those turbine units suck air all the time, evn when the air is damp, and therefore they can add moisture to the attic.

    Here is a quick quote from the Canada Mortgage and Housing Corporation

    "Attic Venting
    If you have properly sealed the attic you should not need more attic ventilation. Attic ventilation is overrated. In winter, the cold outside air cannot hold much humidity or carry moisture away from the attic. In summer, attic temperatures are more affected by the sun and shingle colour than by the amount of ventilation.

    Recent research shows that identical attics, with one unvented and the other vented to code, have much the same humidity and temperature. Attic computer models show that attics in damp coastal climates may actually be drier with less ventilation."

    Here is a link to the rest of the article - http://www.cmhc-schl.gc.ca/en/co/maho/gemare/gemare_001.cfm

    The site has great articles on all sorts of house as a system issues.
  7. PaulRicklefs

    PaulRicklefs New Member

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    oconner the cmhc article is trying to address humidity in an attic space, not ice damming. Ice damming is caused by a higher temp in the attic space. No matter how well insulated a house is the attic will always be slightly warmer due to heat loss than the outside temperature. Proper attic venting helps equalize the temperature between the attic and the roof and therefore reduce the chance of ice damming
  8. jdemaris

    jdemaris New Member

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    Every house is different and problems can be unique. In my area of central New York, ice dams are a big problem. We tend to have weather that is perfect for it. If your upper roof warms up faster then your eaves, it's going to happen, one way or another - if the weather gets right.

    We tend to get more snow here then most of Michigan - and around the same as the worst parts of the Michigan UP. Here what works for some - steel roofs (heat up fast and shed snow and ice), roof raking after every snow storm - and - electric eaves heaters. With the latter, I don't like them, but they do work well. You only turn them on when needed to put a path in the ice dam for water to run. Usuallly installed over metal ice-slides.
  9. oconnor

    oconnor Minister of Fire

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    Based on the title of "Attic Venting, Attic Moisture and Ice Dams, the picture of an ice dam,and the 12 paragraph discussion of ice dams, I think that the authors ( scientists and enginneers who seem to disagree with national building code enough to put it on the agencies web site) think that moisture, venting and ice dams are related.

    There will always be some temperature delta between inside and outside - the problem is when the temp differential isn't universal, and the water freezes again. A turbine is going to pull cold air in around the eaves, and cool the eaves quicker than the rest of the roof - hence it refreezes.

    As the article says (and my post above says too), Recent research shows that identical attics, with one unvented and the other vented to code, have much the same humidity and temperature. Attic computer models show that attics in damp coastal climates may actually be drier with less ventilation.

    Ventillation isn't the problem, any more than blowing your nose cures allergies. Get rid of the source of the allergy, or in this case, the heat. The source is air infiltration into the attic space. If it was just radiant heat passing thru the insulation, there would not be the differences in roof temperature to cause the thaw and refreeze.

    I would go so far as to say that extra vents (like a turbine to suck air out) would make the air temp at the eaves cooler than the resultant temp of the rest of the outside air diluted into the attic space, and would make the temp differential between eaves and roof surface worse, and hence increase the the amount of ice damming.
  10. fabguy01

    fabguy01 New Member

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    I understand what you are saying about the snow thawing and then freezing when it gets tothe eve's, that is what is happening on my house. Ijust got done shoveling the roof it dosent thaw like all my neibors do though, they always seem to have just a few inches of snow with little if any icecicles but I always a get huge accumulation of snow on my roof. While I was on the roof today I noticed that the snow had the same consistency as the snow on the ground, except for what was in contact with the shingles. it is like that all the way till the last 4" of the eves where the dams form"by the way they are 24 eves I dont know if this makes a difference",so what your talking about is already happening without a turbine. all this got me thinking, what if I pot some kind of a blower motor in the attic and used duct work to supply the air to the motor and let it exhaust intothe attic, that way it would blow the warmer attic air out the eve's instead of sucking it in through the eve's, I would think that would help keep the entire roof at an even temp?any thought's? thanks again for everyones help!!! Nate
  11. Hogwildz

    Hogwildz Minister of Fire

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    Soffit venting is useless without either ridge vent or some form of venting higher up on the roof near the peak.
    With a hip roof, you can do ridge vent along the peak, and hip vent along the hips. Problem solved.
  12. oconnor

    oconnor Minister of Fire

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    Nate

    As per the article, and my experience in my own 75 year old house - ATTIC VENTILLATION IS OVERRATED!

    Work to keep the moist warm air from entering the attic in the first place. Caulk the attic hatch shut. air seal around the chimney (be careful with combustibles around it - most need clearance to combustibles, so use the right stuff to seal it) and wire penetrations into the attic. Air seal the ceiling mounted fixtures in the house.

    My house is a 1930's two storey, 4 sided hip roof, 5 of them the same on the block. All the rest have massive ice dam issues. mine doesn't - I installed R60 wet blown cellulose, blown right up against the roof surface except at the vents, but before that I sealed all the wire penetrations, and spray foamed around the chimney (I have a zero/zero flue install, so I can do that and not cause fire concerns), and sealed the attic hatch. My attic has 4 soffit vents in total (1 ft by 8 inch holes) - none in the roof, all in the eaves, and they are all covered with vinyl soffit material. There is very little air getting into the attic, so there is very little heat transfer, and very little moisture.

    Like I said, adding ventilation is like blowing your stuffy nose, it relieves the symptom, but doesn't cure the problem. Put your efforts into keeping the air (and therefore the heat) in the house, instead of trying to figure out how to get it out of the attic.
  13. richg

    richg Minister of Fire

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    Ice dams are caused by warm air leaking from the living space into the attic. You are wasting your time and lots of money with ventilation. The solution is to find the source of the air leaks and stop them. Cellulose is better than fiberglass batts in terms of stopping air likes, but both of them are vastly inferior to spray foam. You have a messy but vital job ahead of you. First, find the air leaks, either by having an inspector with an infrared camera come over (about $300.00), or buy a good infrared thermometer (sears hadware has them), aobut $100-150. Chances are the leaks are coming from attic top plates, around light fixtures, around pipes or anywhere there is a a penetration into the attic. Next, clean the cellulose from around the leak area and shoot it with gun foam. You can get by with Great stuff, but a gun foam kit ismuch cleaner and easier to use. Replace the cellulose and you are done. Notonly with this stop your ice dams, but it will save you big dollars on heating and cooling. Here is a picture of an air leak in my house before I shot it with gun foam two weeks ago. The foam you do see in the picture is from a bathroom remodeling job I did a year before finding this gem of a leak. The insulation is black from dust-laden air moving through it. Good luck!

    Attached Files:

  14. jdemaris

    jdemaris New Member

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    Not always true. Many ice dams, if fact all the ice dams in my area are caused by unequal snow melt on the roof. Many winters in my area will see over a dozen snow storms, many roofs are snow covered most of the winter. When the sun comes out, the roofs heat up and . . . if the entire roof does not all heat at the same rate, ice can form at the eaves and create massive ice dams. The snow heats up high, are freezes when it hits the cold eave.

    Blaming warm air intrusion into the attic doesn't always hold true for several reasons. One is . . . many attics are used as living space and are heating full-time - yet may of those houses do NOT have ice dam problems. The new addition I built on my house hads cathedral ceilings with no attic at all and it's all heated - and gets no ice damming at all. That's because I keep the eaves warm too. But yeah, if you were able to keep your attic as cold as outside, the entire roof might stay a uniform temp. That's kind of unlikely unless you're going to leave all the attic windows open. Even it your attic stays 40 degrees - if the eaves reach a temp fo 20 below zero - you still have a huge temperature differential.

    Ice damming is a big issue around here - with old and new homes. Some newer homes work on the opposite idea as you mentioned. They super-insulate the eaves so they can stay warm. Warm eaves prevent damming. Many homes have electric grid heaters insalled in the eaves.

    Ice damming is one of main reasons why many in my area, and also in the nearby Adirondack Mountains, are installing standing-seam steel roofs. They tend to release ice dams very quickly - which, in itself, can be a problem.

    Parts of my house were built in 1820 and 1870, and it has a soldered, standing-seam steel roof. If the roof builds up a lot of snow, and I don't rake it, it's often 2 - 3 feet deep. When the sun comes out, some damming starts - but then we get huge ice-slides coming off. In fact, they broke apart two front porches I built until I finally went with no front porch at all. Easiest way to prevent these big slides is to rake the roof and not let it get deep up there. But, I kind of like having deep snow on the roof as added insulation.
  15. oconnor

    oconnor Minister of Fire

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    Dude, insulating the eaves doesn't keep them warm, it keeps them cold. Say what you will, I'll stick to the proven solution - keep the heat from the house out of the attic.
  16. jdemaris

    jdemaris New Member

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  17. oconnor

    oconnor Minister of Fire

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    Proven by CMHC and those who deal with building code. Haven't built any houses - but lots of stupid people have built lots of houses - that doesn't make them right because they are prolific, it just makes them prolific. I would rather look at the laws of physics than the wisetales of prolific builders.

    On this we agree. Even roof temps is what I have been advocating in my posts above

    On this, I say deal with the problem - the "semiheat" that enters the attic. That heat heat rarely enters thru radiation, it enters thru air infiltration. This is in fact what you are saying - "if heat escapes downstairs and ...."

    My issue was with your earlier statement that insulating the eaves keeps them warmer - it just doesn't work that way. Insulation prevents heat movement from warm to cold area - insulating the eaves keeps them colder, and contributes to the uneven heat you mention - if you have heat entering the attic.

    Insulating the eaves cannot keep them warmer - simple physics.
  18. Hogwildz

    Hogwildz Minister of Fire

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    I have to laugh. When you insulate right to the underside of the roof decking, which in most homes is either plywood, pressboard or planks, you are keeping the wood from breathing on the underside and will cause the wood to rot. Say what you will. I roofed for many years for a living and replaced many roof decks do to homeowners, uneducated overnight builders etc, insulating right up the the underside of the wood roof decking. When it comes time for a new roof, figure in for new wood decking & the labor to tear the rotted old stuff out, dumpster etc.

    The whole reason for unused/unfinished attic space venting is in the summer to allow humid hot air to be replaced with cooler outside air, therefore reducing heat build up which ultimately reduces cooling costs by letting that oven stay much cooler. In the winter it lets colder air ventilate thought the unused space to equal near outdoor temperature. Hence when there is snow or is on the roof, there is less melting refreezing caused by warmer air being trapped in the attic.

    I absolutely agree to seal of any penetrations, gaps etc from the ceiling of the living space below. Sealing an attic door with caulk if the attic is used, is not very realistic, unless you want an ugly mess of built up caulk and redoing it every year. There are covers made for light boxes, attic doors etc that do the same job with no mess. Sealing these penetrations in some manor does do a world of difference, and minimizes heat loss. Also does a good layer of insulation on the floor of the attic. But even the best sealed attic floor will transfer some heat from below. That is were the venting matters & does its job. If proper amount and top & bottom venting is installed correctly it will do its job. But when air leaks from below the attic are present, now the venting is not only taking the air it should be from outside to equalize the attic temp, but also taking warm air from the heated space below, thus hampering the equalization to outside temps.

    Ice damning is caused by snow/ice melt on the outer roof surface melting in the sun and refreezing at night & on warm to colder days. If the home is losing a good bit of heat through poorly sealed ceilings, then yes this contributes to ice damning also.Gutters frozen over also cause damning. This is where ice & water shield protest the eave edges if by chance the damning in the gutters backs up under the shingles.

    Bottom line is:
    Sealing that ceiling below is absolutely top priority.
    Soffit vent equaled with ridge/hip venting does its job if properly set up & installed.
    Insulating up against the bottom of a wood decking will rot that wood out. Seen it many, many times, and it sucks to replace. Especially true but not limited to cathedral ceilings that rely on air coming in the bottom and exiting extremely hot air through the ridge or hips. That is what they make baffles for, that keep the insulation a couple inches away from the underside of the deck. Wood needs to breath, if it doesn't it either dry rots, rots from mold, or both. Just like folks that paint cedar siding & roofing. It rots underneath the paint. Wood needs to breath.
    Not enough moisture=dry rot, too much = mold rot.
    Believe what you will, your in for a major disappointment down the road.

  19. jdemaris

    jdemaris New Member

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    I plead ignorance since I have no idea what CMHC is, nor have I ever heard of a "wisetale." Wivestales, yes. Regional terms perhaps?

    In regard to dealing with state, county, and city codes - I've dealt with residential building and electrical codes my entire working life, going back to the 60s when few codes were enforced, to present. Never had trouble passing the first time.

    In regard to your "simple physics??" If you have an open, uninsulated eave sticking out far from a heated building (24"-30" is common here), and the upper roof gets some warming (from heated rooms below or the sun above) - ice damming can occur. Especially if some of that roof is insulated, and some is not. In that situation, in some homes, opening the heated area so some heat can reach that eave - and insulating that eave to keep it warm - often eliminates the ice-dam problem. In all cases and in all homes - NO. That's why it is far from simple as you say.

    In regard to some other posts about the problems with insulated roof-rafter areas instead of unheated attics? Yeah, could be, we'll see. The jury is still out on that one. There have been many homes built with Cathedral ceilings and foam-filled structured panels - and they are completed filled with poly-iso insulation with zero ventilation. Will they rot over time? Haven't heard of it being a proven problem yet. There are two schools of thought on ventilation that are popular. One being no ventilation is needed if an area is completely insulated with no large voids (like poly-iso panels used in roofs and walls) - and the other being that of keeping insulation from touching sheathing and ventilating it.

    I've been around the building trade long enough to see many "new ideas" fail, and still see some old ideas work very well.

    I own three homes, all in lousy climates - central New York, New York Adirondack Mountains, and northern Michigan. I've eliminated my ice damming problems just fine. Two have unheated attics and one has insulated Cathedral ceilings.

    My wife's parents have a new home in northern Michigan - made entirely from fully insulated structured panels. Fully insulated eaves. No ice damming.
  20. oconnor

    oconnor Minister of Fire

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    jdemarris

    If you don't know what CMHC is, then you haven't read the source of the info in my post above, which I included a link to in a post above - hence, you are arguing with me without having read where I am taking my info from. Read the link. CMHC is the Canada Mortgage and Housing Corporation, a government entity that does research and testing concerning housing and building issues to allow for improvements to code over time. As well, they promote solutions to the problems that design flaws in older buildings, like most of the houses we are talking about with the ice problem.

    Please read the document, and then we can discuss the document. It isn't about who has built more houses, or who has fixed more roofs, this forum is about getting the right info out there, and challenging statements that seem incorrect. Your original statement about insulating eaves did not make any sense to me on its own, as it implies shoving insulation in the gap between the wall top and the roof deck, and extending it out to the roof edge. Perhaps that is not what you meant.

    Folks don't have to agree with me - the info is not mine, that is why I provide the source of the info, so that others can read it, and assess it on it's own merits - not on who can argue the best in text.
  21. jdemaris

    jdemaris New Member

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    I responded to comments that YOU made, not to something in a document, on-line, somewhere.
    Subequently, I'm not out of line for not scutinizing the CMHC documents.

    If I was building a new home in Canada, perhaps I'd have to. But, I'm not. When building new here? There is much to be sifted through - some good, and some rediculous.

    I'm not trying to discredit anything you've read - especially considering I haven't read it myself.
    I am also not going to discredit building practices that work in the environments I've lived and worked in, that I've witnessed, first-hand -over a period of 40 years.

    As I stated previously, home and home problems vary greatly. So do individual solutions.
    And I'll state one more time - sometimes insulating eaves, and allowing heat to enter them, elimates ice-damming issues depending on that particular problem. If that violates the laws of physics - seems there must be a flaw in those laws that are cited.

    I'll also add that . . . in the few stuctured panels homes I've seen in the northeast - with full poly-iso insulation, ridge to eave, with no air space . . . the eaves seem to heat very fast when the sun hits them - due to the insulation in them - and this too helps eliminate dams. This, I guess is a sort of converse situation - where the insulation does not let the sun's warmth pass through and instead, helps to heat the eaves. This is just an anecdotal observation on my part, nothing more.
  22. gpcollen1

    gpcollen1 Minister of Fire

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    Ill just add that ice damming can indeed be solely caused by the location of the portion of the roof. Only about 1/6 of my roof has an issue. The primary cause of the issue is the amount of sunlight this portion gets - just enough to melt it some up top and then that moisture freezes down near the roof line and in the gutters - slowly causing issues. I just stay on top of it these days with my broom, shovel and hoe. I said primary issue b/c I cannot guarantee that no heat escapes my house of course.
  23. oconnor

    oconnor Minister of Fire

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    I have also heard of ice damming starting up after the install of a new wood burner, as a result of the flue, now heated more than when the flue was less used, that passes thru the attic space. That is one I'm watching this winter, as my fireplace was rarely used until I installed an insert, and now we run it all the time.
  24. fabguy01

    fabguy01 New Member

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    thanks for everyones oppinions, By just listening I think I will use a little bit of everyones oppinions seal the heatout is #1. but I am sorry oconnor since I've started this thread I've asked numerous locals about ventilation, some builders some not and others who are stricktly roofers, ALL OF THEM" approx15 people" ALL agreed with Hozwild. So #2 will be adding a ridge vent, turbine or some other type. Just one more question Im thinking after i make sure all air leaks are repaired i would like to add more insulation bot i currently have a blown in insulation layer with fiberglass batts over top.I think im getting alot of heat loss in spaces bettwen the bats, can i add blown celluose over and inbetween the fiberglass? Thanks Nate
  25. oconnor

    oconnor Minister of Fire

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    You can add it over the fibreglass, but you will compress the batts and lose R value. I'd recommend you add wet blown cellulose - the adhesion of the fibres can assist in keeping air infiltration out. No need to remove the batts, but the R value will go down with any compression.
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