Damn Ice Dams

This is picture of a small portion of my late 19th century house.  This is a bit of the unfinished portion of my attic.  The shot is taken between two of the rafters.


The half inch thick lumber that forms the roof is shown, along with a few roofing nails that have come thru from the other side.  Below you can see the floor of the attic and a small drift of insullation left behind from when it was blown into the side walls.  Somebody, probably the contractor, did the right thing and raked it away from the eves.  At the very bottom you can see into the box that forms the eves.  We had rebuilt some years ago, which is why the wood in there has that coat of white primer on it.

Each year this portion of the room forms a vicious ice dam.  It rains onto the entrance porch and leaves a glaze of ice.  It was the there one of the days the agent showed us the house decades ago.

Ice dams form because the snow on the roof melts. That happens because the roof is warm, it shouldn’t be warm.  The water then flows down till it gets to a cold spot, often the eves, where it freezes.  Maybe you get a dam maybe you just get icicles.  We mostly just get icicles.  That’s good, since if you get damns the water on the warm part sometimes forms pools that work their way thru the roof and damage the interior.  That’s bad because it implies that my eves are being warmed, presumably by warm air traveling up the wall cavities.

Click to Enlarge

Click to Enlarge

I tried to address this problem when we had the roof done and the eves repaired.  The textbooks prescribe that you need to get cold air to flow up the interior surface of the roof.  Entering thru vents in the eves, and exiting thru a vent along the top of the roof.  When we had the roof done a decade ago that’s what we bought.  The eve vents are little one inch holes filled with little aluminum widgets that let the air in and keep the bugs out.

I have another picture like the one above with the lights turned off.  The problem is, it’s entirely black.  No light, and so I presume, no air is getting in from outside.  There are five pairs of rafters in the portion I was inspecting today.  In only one of them is light leaking in.  I feel a slight cold draft in that one, just as I should.

My vacuum cleaner’s hose isn’t long enough to reach into these cavities.  What to do, what to do?

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