An ice dam is a ridge of ice at the lower edge of a roof, usually with icicles hanging off it and sometimes with water backing up behind it. It forms when heat escaping from the house warms the roof deck, snow on that warmed surface melts, the water runs down toward the eaves, and there it reaches roofing that sits over unheated space outside the walls of the house, where it refreezes and builds.
That sequence is worth sitting with, because it explains why ice dams are an attic problem before they are a roof or gutter problem. The ice is not forming because your gutters are wrong. It is forming because part of your roof is warm and part of it is not, and that temperature difference is being created by heat leaving your living space and reaching the underside of the roof deck.
The first is conduction: heat moving through the ceiling material itself, which is what insulation slows down. Thin, settled, uneven, or missing coverage lets more heat through, and the pattern of dams on a roof often lines up with where the coverage is worst. The perimeter is a frequent offender, since the space where the roof meets the exterior wall is tight and gets shorted, and that happens to be the area closest to where dams form.
The second is air movement, and it is usually the bigger contributor. Warm air rising through unsealed openings in the ceiling plane, through the attic hatch, around can lights, up open wall cavities, and through chases carries far more heat into the attic than conduction does. This is why houses with a good depth of insulation still get dams. The material is doing its job and the air is going around it.
An attic that is properly vented moves outside air in low at the eaves and out high at the ridge, which keeps the attic near the outdoor temperature and keeps the roof deck cold and uniform. When that airflow is blocked or unbalanced, whatever heat does get into the attic lingers under the roof deck instead of being carried away, and the melting pattern that produces dams becomes far more likely.
The most common way this gets broken is insulation itself. Material blown or pushed out to the perimeter can bury the soffit vents that supply intake air. A homeowner adds depth, the attic gets warmer instead of colder, and the ice gets worse the following winter. This is why any competent attic job includes keeping intake airflow clear, and why insulation and ventilation get discussed together rather than as two separate purchases you can make in either order.
Gutters are where the ice becomes visible, so they get the blame. Cleaning them, heating them, or replacing them addresses the place the symptom appears without touching what causes it. Heat cables can keep a channel open through the ice and prevent some water damage, which is a legitimate mitigation, but the roof above is still warm and snow is still melting where it should not be, and the ice will keep forming as long as that is true.
The damage that matters usually is not the ice on the outside. It is water backing up behind the dam, working under the roofing, and finding its way into the roof deck, the attic, the insulation, and the ceiling below. That is why a house with recurring dams is worth having someone inspect from the inside. What is happening in the attic is the story, and the eaves are just where you can see the ending.
The best time to look is not during a storm. Have somebody go into the attic and check whether the ceiling plane is sealed, whether coverage reaches the perimeter, whether soffit vents are clear, whether bath fans are venting outside instead of into the attic, and whether there is staining on the sheathing that says water has already been in there. Those five checks explain most recurring ice dam situations.
It is also worth being honest about what insulation will not do. A roof with a genuine leak, a section of roofing installed without proper protection at the eaves, or a complex roofline that traps snow may need a roofer regardless of what happens in the attic. Insulation and sealing address the heat side of the equation. If a contractor tells you they can eliminate every dam forever, that is a promise nobody in this trade can honestly make.
No. Insulation reduces heat moving through the ceiling, which helps, but air leaking through unsealed openings and blocked attic ventilation are often the larger contributors. A roof shape that traps snow can also play a part. Insulation, sealing, and ventilation together give you the best case, and no honest contractor will promise you a guarantee.
It is worth a look. Icicles alone are common and are not proof of damage. Ice that builds into a solid ridge along the eaves, with water pooling behind it, is the version that gets under roofing. Checking the attic for staining on the sheathing and for damp insulation tells you whether water has already been getting in.
Chipping at ice risks damaging roofing and risks you falling. Removing snow from the lower part of the roof with a roof rake from the ground is the safer short-term step. Neither addresses the reason it formed, so treat it as getting through the winter rather than as a fix, and have the attic looked at once things thaw.
Cold rooms, drafts, ice at the eaves, or an attic you have never been in. Any of it is a place to start.