1. When do the icicles or ice ridges form?
2. Where on the house?
3. Is snow melting off the roof while it stays on the ground?
4. What is the attic like?
5. What are you doing about it now?
Why Heat Loss Is the Cause
Heat escapes into the roof assembly
Through gaps around light fittings, the attic hatch, plumbing stacks, wiring penetrations and the top plates of interior walls — and through insulation that is thin, compressed or missing at the eaves. Air leakage carries far more heat than conduction through insulation does, which is why air sealing comes before adding depth.
That heat melts snow from underneath
The roof surface above the heated space rises above freezing while the outside air stays below it. Snow melts at the deck, not at the surface, which is why this happens on days when nothing else is melting.
The meltwater runs down to a cold eave
The overhang has unheated air beneath it, so it stays at outdoor temperature. The water reaches it and refreezes.
The ice ridge grows and water backs up behind it
And standing water finds its way under roofing that was designed to shed water downhill, not to hold it. That is when it appears inside, usually as a stain at the top of an exterior wall.
Notice what is absent from all four steps: the roofing material. Change the covering and every step still happens. That is why a metal roof reduces ice dams — by shedding the snow before it can melt — without fixing them.
Three Rules for the Meantime
Rake from the ground, with a roof rake. Clearing the first few feet above the eave after a heavy fall genuinely reduces dam formation. Do not get onto a snow-covered roof — people are seriously injured doing this every winter in this region, and a metal roof under snow is as slick as anything you will ever stand on.
Never chip at ice. Not with a hammer, not with a shovel, not with an axe. You will damage the roofing, the flashing or yourself, and the ice will be back within a week because the cause has not changed.
Heat cables are a stopgap, not a repair. They keep a channel open so water can escape, which prevents damage. They do nothing about the heat loss causing the dam, and they add running cost every winter. Reasonable while you plan the real fix; not the fix.