More Building Science
Ice dams are a common problem in many of the existing homes in my area of Grand Rapids, Minnesota, climate zone 7. In my neighborhood alone, the number of homes with this problem reaches into the double digits. I’ve noticed that the intensity of ice dams seems to change from year to year, and that this year seems to be a bad one.
最近，我与绝缘承包商和总承包商一起从事冰坝诊断工作。这座房子建于1990年代初期，有证据表明冰坝是一开始是一个问题。我们花了几个小时测试这个房子。我将分享我们在这里发现的东西。
Why ice dams form
It’s simple: In areas that receive snowfall, snow will accumulate on the roof. Some mechanism (I will get into this below) causes the roof sheathing to warm beneath the snow, which makes it melt. As the liquid water runs down the roof, it meets the roof eave, which is cold, thereby causing the liquid water freeze. The ice builds up over time until it eventually forms a “dam.” Often, this accumulation creates icicles that hang on the eave, which can be dangerous.
那么，是什么导致屋顶护套变暖呢？房屋朝南一侧的深色壁板会产生热量，从而向上移至屋顶甲板。机械通风和燃烧排气排出房屋附近的墙壁也可以产生足够的热量以融化雪，尽管根据我的经验，这些原因不太常见。更常见的是位于无条件的阁楼中的强制空气管道。
By far, the biggest culprits when it comes to ice dams are air leaks at the ceiling or upper wall, attics with inadequate insulation levels—especially near the…
3 Comments
Ice dams can be eliminated by working from the inside but it takes effort. I prefer a vented attic in our MN climate. A cathedral ceiling can be opened from the warm side and a ventilation channel beneath the roof deck can be established from the eave to the ridge. The remaining rafter space is filled with batt insulation. To bring the ceiling insulation to code level, strap polyiso sheets beneath the rafters with seams foil taped. The new ceiling can then be put in place. This method works and would be cost competitive to the alternate method of insulating the existing roof deck. Also the work can be done anytime during the year.
Good advice Doug! I see this done on occasion, and you are right, lots of work, but so is the alternative. I'd also add having a blower door test completed before adding the ceiling finish. Sometimes that wall to ceiling transition is tough to get a good seal unless you can remove enough wall finish to get to the wall air control layer.
The best thing we can do as builders is get the details right when building new. Some of these repairs are very expensive and disruptive to the homeowner when fixes are needed.
For our Minnesnowda house (6A) we created a 2 inch vent between rafters and then sprayed close cell foam to help air seal the attic. Then buried all of the A/C vent in 16 inches of fiberglass. That eliminated the ice dams on the south facing side.
登录或成为成员发表评论。
Sign up Log in