Ice dams in gutters: is the gutter the cause or the victim?
Ice dams in gutters look like a gutter problem. Most of the time they are not.
When ice dams in gutters show up, the gutter is rarely the cause. It is where the ice collects. The cause is heat escaping into the attic and melting the snow above it.
Why the ice ends up in the gutter
Warm attic air melts snow on the upper roof. The water runs down to the eave, where the roof is cold, and freezes. The gutter sits right at that cold edge, so it fills first.
A full gutter then holds the ice up against the lowest shingles. That is the point where a gutter ice problem turns into a roof problem.
What the ice pattern tells you
Look from the yard. Ice that is thick over the whole length of the house points to heat loss across the attic floor. Ice in one patch usually sits below a bathroom fan duct, a recessed light or a chimney chase leaking warm air.
Icicles hanging from the gutter lip mean water is passing over the top of the ice. They are a sign, not a threat to the roof. Keep people and cars out from under them.
Do gutters cause ice dams?
Sometimes they make things worse. Gutters packed with leaves hold water that freezes into a solid block. Sagging runs trap meltwater in low spots. But clean, level gutters on a leaky attic still get ice.
Cleaning them in autumn is worth doing. It will not stop the dam by itself, so do not expect it to.
What we do not tell you to do
We do not publish steps for chipping ice out of a gutter, cutting channels or pouring anything on it. All of that means standing on an icy ladder or the roof edge, and a gutter bent by ice is a cheap repair next to a fall. If ice is pulling the gutter away from the house, keep clear and call a roofer.
The fix is in the attic
Seal the air leaks in the attic floor, add insulation and keep the roof deck cold with working ventilation. Start with what causes ice dams. For ice that is already there, see ice in gutters.
Frequently asked questions
Why do ice dams form in gutters?
Meltwater from the warm part of the roof refreezes at the cold eave, and the gutter is the first thing it reaches. Heat loss from the attic is the underlying cause.
Can clogged gutters cause ice dams?
They can make a dam bigger by holding water that freezes solid. They do not cause the melting. A leaky attic floor does.
Should I chip ice out of my gutters?
Not from a ladder or the roof edge. Hammering also bends and cracks gutters. If it is a problem, a professional crew can steam it off safely.
Do icicles on the gutter mean I have an ice dam?
Often, yes. Water is running over a ridge of ice at the eave. Check the ceilings along the outside walls for stains.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- NOAA / National Weather Service. Winter — National Weather Service safety hub
- NOAA / National Weather Service. What To Do If You're Caught in a Winter Storm