· Michael Blair
Middle Tennessee gets a handful of freeze-thaw events each winter, enough to damage gutters and cause ice dams on poorly ventilated roofs. Because it is occasional, houses here are rarely detailed for it.
What an ice dam is
Heat escaping into the attic melts snow on the upper roof. The water runs down to the cold eave, refreezes, and builds a ridge. Water then backs up behind it and under the shingles.
It is a heat-loss problem before it is a gutter problem, which is why gutter modifications rarely solve it.
Why the fix is in the attic
Air sealing the ceiling plane and insulating adequately keeps the roof deck cold, so snow does not melt from below. Balanced ventilation carries away what heat does get through.
That is the durable fix. Heat cables manage the symptom and cost money to run every time they are on.
- Air seal ceiling penetrations, especially can lights and the attic hatch
- Insulate to an adequate depth, evenly
- Balanced soffit and ridge ventilation
- Keep gutters clear so meltwater can leave
- Heat cable as a last resort, not a first response
What ice does to the gutter itself
A gutter full of ice is extremely heavy and pulls hangers out of the fascia, particularly spike-and-ferrule fixings and thin-gauge gutter.
Blocked gutters make it worse, because standing water freezes where flowing water would have left.
Before the first freeze
Clear the gutters and confirm the downspouts run. That is the single most useful winter preparation, because a clear gutter drains rather than holding water to freeze.
And check the attic while you are at it: blocked soffit vents and insulation pushed into the eaves are what set up an ice dam in the first place.