I recently insulated a 3 story home with 9/12 pitch with 2 lb foam . We sprayed the foam over double tru vents the whole length of rafter down to the top of the knee walls. we then sprayed the knee walls and blew 12 to 14 inches of cellulose on the remaining part of the attic floor behind the knee wall . The soffits to not allow air into the area to push any warm air up the chutes and out the ridge vent. We have significant ice damming where i thought we would have no heat loss. cant figure out where the heat loss would be to melt this much snow. need help
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You're saying you blocked the soffit vents?
they were blocled, its an old house. I am thinking my customers should have perforated soffit and truvents put in to push cold air up the underside of roof to cool it
Were there ice dams before the insulation was installed?
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
that is the odd thing, they never had much at all for dams. Maybe because it wasnt heated before. They actually closed off the regiters the other day cause since we spray foamed it with 2 lb foam it is too hot. I nean there were dinasour type icicles on this house, it was and is unbelievable. I assumed that it being so well insulated that heat loss wouldnt be an issue and the need for ventilation wasnt there
Are you saying this is newly remodeled -- an attic conversion?'Splain yourself, Lucy!
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Yes it is a 100 year old house and we finished the attic, so if tou can picture the typical 2 roof slopes with 4 foot knee walls. Slopes are foamed at leat 6 inches and knee walls almost full ,they are 2x4. On the 4 foot of floor behind that I also foamed the heat duct laying inthere and then blew R- 50 of celluose over that and up against the knee wall. It is in this area that you can see the soffit that is solid wood. Somebody drilled a few holes in it before installing vinyl over but hardly any air to speak of. We finished the whole thing for bedroom and games room
Yeah, previously the attic was unheated, and heat from below could escape. Now it's being trapped in the kneewall area.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
that was my thoughts exactly
And you didn't see this coming?
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
I also have an old house, and I and all around me, from my observation, get ice dams, generally on the south side, of course, where the weak sun melts roof top snow but can't keep it from freezing in the gutters and backing up. I've avoided leaks by having 3 to 6 feet of membrane under the roof at the eaves. This has worked for many years and should be a part of any northern roofing. The attic can contribute to it, but I think it happens anyway, at least where I live.
I think you illustrate that there are two sources for the heat that causes the problem: The house and the sun. Simply insulating the attic ceiling well doesn't deal with the sun issue.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
I think that you understand the situation, as there are lots of contractors in our area who, I'm ashamed to say, do the attic insulation and ventilation scare tactic for business. Some years I have ice dams, others I don't. No change in my attic. I'm happy that I have the roof sealed underneath the shingles. Haven't had a leak in sixteen years of variable weather in my latest new old house. I also don't have snow slumps on my roof, so I think I'm okay.
I don't think heat is being trapped behind the kneewalls, in fact, I think it's exactly the opposite. The areas behind the kneewall, and hence the lower portion of the roof above the area behind the kneewalls are now much colder relative to the rest of the roof. I think you have simply increased the rate of melting in the upper roof area by heating that area. Six inches of foam is maybe R-30 at best. That doesn't qualify as a well insulated roof in my opinion.
Edited 2/9/2009 11:44 pm ET by RedfordHenry
Yeah, it's not clear how much insulation was installed, how much ventilation there is, etc. Nor can we tell from the posts where on the roof the bulk of the melting is occurring. It does seem clear that it was not well thought out -- foam isn't a magic bullet that will solve all problems.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
you describe what you did at the kneewall area, but what about further up towards the ridge?
What could likely be happening is that you have a nice cold eave but are losing heat up high. That melts the snow, which runs down until it hits the colder area of the roof and starts to freeze.
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