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damn ice!
Monday, February 2 2009
As I went about my various tasks today, I happened to notice an unexpected puddle of water —less than a teaspoon, mind you— on the window sill of the the first floor half bathroom. Hmm, that was odd. Where had it come from? My eyes immediately went toward the ceiling and scanned downward. That was when I saw a leisurely drip coming past the moulding at the top of the window. There was water in the wall. But how had it gotten there? There were two possibilities: either there was a plumbing problem or there was finally too much fucking snow on the roof.
I went outside to look, but the roof was far above that window and there was a wide overhang to protect it. So then I went upstairs into the teevee room and looked around under a little shelf that protects a series of pipes coming from the adjacent bathroom. The pipes seemed to be fine, but there was a small amount of water near where the floor met the sloping ceiling. It seemed the water was coming from the roof valley overhead, a valley whose ice-choked nature had been concerning me for the past couple weeks. We were suffering the nasty effects of an ice dam.
In a normal winter, we don't suffer from ice dams. But this winter has been unusual in two respects. There has been a lot of precipitation but no good thaws. Consequently, the snow has built up and like volcanic ash, gradually compressing itself into a solid mineral. The snow does melt when the sun comes out, which allows it to melt from the roof and run down to the eaves, where it immediately refreezes into ice. The eave-based ice has accumulated for weeks without ever being melted back by a thaw. Today was sunny and temperatures reached into the 40s, but that just meant that some of the snow melt from higher on the roof had nowhere to go but into the house.
To confirm my suspicions, I went to the other side (the south side) of the west-facing gable and looked at the window just beneath the roof valley. Sure enough, there was water dripping from it too. Interestingly, there were no such problems under the east-facing gable, which is designed somewhat differently (the valley doesn't reach all the way to the edge of the roof line). Also, the house gets much more exposure on its east side (which also is oriented somewhat southeast), and any nascent ice dams are quickly destroyed by solar energy.
Usually when a house is plagued by ice dams, the problem is that the house has insufficient insulation and the roof itself is poorly ventilated. These aren't really factors in our house. There isn't an attic beneath the roof, but the joist bays are full of insulation and there is a ridge vent. But because there are two roof ridges meeting at right angles, there can be no ventilation from below for that part of the roof that forms the sides of the valleys. Still, I'm pretty sure that the melting of snow high on the roof is the result of sunlight from above, not leaking heat from below. The effect, though, at least this year, is the same. Evidently a lot of people are having snow-related problems with their roofs this year; yesterday Gretchen and I saw signs advertising the service of roof snow shoveling. The price: fifteen cents per square foot. (Our roof would cost us at least four hundred dollars, but I can't imagine trusting some random yahoo to take a shovel to it.)
I used a hammer and a cold chisel to open up the lowest foot or so of the valley, hoping that meltwater would open up ice caves through the blockage. It was a miserable job and I didn't make much progress. You can bet that in subsequent years I will be more vigilant for this particular problem.
For linking purposes this article's URL is:
http://asecular.com/blog.php?090202 feedback
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