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I live in Michigan and just built a house. This is the first winter and I have ice build up on my eves (bad). I have a 6/12 pitched roof up and over nothing fancy standard truss heal, ridge vented, soffit vented every 3rd and blown fiberglass in attic. The insulator says he has plenty of insulation and it is packed tightly at the tails. He says that there is not enough air flow or ventilation in the attic. I don’t know what else I could do as for as venting goes? I’m looking for some input or a solution to the problem? Any advice would be greatly appreciated.
THANKS JEFF
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How much insulation do you have? You should have at least 12"(R-38) fiberglass batts or 14"-16" blown fiberglass that equals a (R-38) in zone 2 & 3, and a (R-30) in zone 1 in the State of Michigan. If you have at the proper amount of insulation, I would start looking for a air sealing problem. I wouldn't blame the venting right away, because the venting should be in place only as a back-up. The proper amount of insulation and air sealing are of much more of importance. Also when needing alot of insulation 10" or more, you should go with a 10" or higher heel height on the truss so you can get the proper amount of insulation at the most crucial part, where the roof & wall meet.
*"The insulator says he has plenty of insulation and it is i packed tightly at the tails. He says that there is not enough air flow or ventilation in the attic. "What do you mean: "packed tightly at the tails." Has be blocked off the air flow from the soffits?I'd have someone else check the insulation: another insulation contractor or a home inspector (check their practice for walking in attics, some are more conservative than others.
*Jim thanks for your reply. I measured the thickness of the insulation in some areas it is about 16"( blown fiberglass),there is some high and low spots. You mentioned air sealing problems could you explain?
*Jeff, simple things like holes for wiring, can lights, plumbing penetrations, any kind of chase from the basement/crawl to the attic. How bout where are the baths vented to?
*Thanks, CalvinThat pretty much covers what I was getting at.
*Now that it is cold look around in your attic to see where the frost is. Also any other signs of venting from the rest of the house into the attic: There should be NONE.Then you need to take another look at ventilation on top of the insulation. There should be a clear path from the eave to the ridge throughout the entire roof cavity. The idea is that the roof cavity(attic) is at ambient temperature and free of any leakage from the rest of the house. This can be done a variety of ways. Which is best for your house can best be determined by an on-site inspection by someone who knows what they are looking at. For sure you don't want any tightly packed insulation since it is the dead air space between the fibres/particles that gives a good chunk of the insulating ability.So, the ice tells you that you have either leakage problems, or ventilation problems, or a combination.
*Thanks to everyone for the responses. I don't think this going to be easy to figure out, I have some can lighting to seal off. any suggestions on the best way to do this?? All this is new to me. It is cold in the attic. And I do have frost on both eve ends of the house? I found some areas of the attic to have less insulation then it should have, it measures around 10"-14". I don't feel allot of air moving around is this normal? JEFF
*Jeff, you are using your observations about the condition inside the attic and can get misled by them."It is cold in the attic" "I don't feel alot of air moving around"Both are true to you because your body is almost 100F (body heat 98.6F). Remember that the ice is formed when the temperature reaches just above 32F, so a human body is a poor instrument to judge what is going on inside the attic space.Keep also in mind that the process we are concerned with here is occuring with great patience. A very small amount of warm air escaping from your warm ceiling at a very slow rate can reach the roof and still retain enough of its heat energy to get the roof temp above freezing if it is a steady enough flow. You may not be able to observe this by visiting the attic - frost may exist in one area but warm air could still be melting roof snow somewhere else.I think that the BEST way to catch sources is to look at your roof, from the outside, after a light snow or hard frost has put a nice even layer of white on to your dark colored shingles.You should now be able to see quite clearly where the warm air is in your attic because that's where the 'white' is missing! I suggest that you do this after you have sealed up all the obvious leak sources first, like getting rid of can lights and sealing existing holes in your attic floor - check the archives for techniques to seal up around can lights, but I think they are a BAD idea (in cold climates) in attic floors due to this ice daming problem!.If after you have sealed up everything you can find, including any open stud bays, wire chases, can lights and attic stairs you may STILL find some quickly melting spots on your roof (keep checking the roof throughout the heating season whenever there is a light dusting of snow so that you can see the effect of different types of weather (wind) or usage of the house (extra guests, fireplace use, etc). These melted areas could be caused by a small leak in your attic stair seal, or something like that. I have found that applying the foam vent channel stuff to the underside of the roof sheathing will then provide just a bit of insulation to prevent any more melting in these areas. Note that I suggest to add insulation/vent channel to the roof last. This is because I think it is a last resort. Close the leaks first, and only after you have gotten that as good as you can then mask the symptom last. You can use the frost on the roof method to find out the few places where insulation / vent channel will be helpful and just put it in those places.In your house you will have to be VERY meticulous sealing up every tiny hole in your membrane (the ceiling of every room below your attic) because fiberglass is quite willing to allow all warm air to flow thru it freely. One thing you may consider if just sealing up holes does not seem to help you much is to blow a layer of cellulouse on top of it to act as a barrier to this warm air flow.
*Snow melt and frost melt patterns can be very helpful. You are paying to melt the snow. 1000 btu's for every pound of ice, probably leak 2 or 3 times that into the attic but the venting masks the problem.Dare I suggest getting in touch with a building science type of person? Maybe someone with a blower door and infra red camera?-Rob
*Rob, you heathen. Those things are the tools of Satan. Too expensive too. And nobody does it that way around here. Too. Joe H
*Gotta support looking for leaks. My mother in law had us look into her ice prob. We were confused there was a ridge vent/ venting at sophets sufficient ceiling insul. blown in cellulose above 1st floor. Then we pulled the plywood wall panels off and found everything was wrapped up but when you crawled into the spaces all false interior walls were uninsulated. The bleed from her heating system was heating these spaces around the sophets and huge Icicles were forming. Plenty of insulation is not always the prob. She had tons it was just in the wrong places.
*Many good thoughts and suggestions. Look closely at venting making certain there is free flow between soffits and ridge and that ridge vent is not blocked by insulation fibers. Also be aware that some ridge vents work better than others and when covered with snow they lose venting ability. I'm in Marquette MI and see many problems with ridge venting - thus gable venting a good backup unless want to keep clearing ridge of snow during winter.
*I agree...that the forced air system must be flowing up into the attic bigtime... Interior walls can be sealed in the attic... blown fiberglass is a terrible air seal. I would never use the stuff. Recessed cans are another major no no in insulated ceilings.All can be fixed. Time to call Fred Lugano or Rob.near the stream,aj