Freeze-thaw at the flashing in Bismarck
About 98 days a year cross freezing between night and day but only 0 cm of snow falls, so the damage lands on the chimney and gutter detailing rather than at the eave.
About 98 days a year cross freezing between night and day but only 0 cm of snow falls, so the damage lands on the chimney and gutter detailing rather than at the eave
Bismarck crosses freezing between night and day on about 98 days a year, and each of those cycles melts a little roof snow and refreezes it lower down.
How the damage actually happens
Heat leaking into the attic warms the middle of the roof deck while the eave, which overhangs unheated air, stays below freezing. Snow melts up high, runs down, and refreezes where the deck is cold. The ridge of ice that builds up holds the next lot of meltwater against the shingles, and shingles are designed to shed water downhill, not to hold it.
The median home in Bismarck dates from 1985, so most roofs here are on their second or third covering and the detailing underneath is of that era.
What actually fixes it
- Air-seal the attic floor so heat stops reaching the deck - this is the real fix
- Insulate to the depth the code calls for, after sealing, not instead of it
- Ventilate soffit to ridge so the deck stays close to outside temperature
- Only then consider membrane at the eave, which limits damage rather than preventing ice
Heated cables are the opposite of a fix: they melt a channel through the ice, use electricity every winter, and leave the cause untouched. They have a place on a roof that genuinely cannot be ventilated, and nowhere else.
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