What an ice dam is
The University of Minnesota Extension defines an ice dam as a ridge of ice that forms at the edge of a roof and keeps melting snow from draining off. The water that backs up behind it can leak under shingles and into walls, ceilings and insulation.
For an ice dam to form, three things have to happen at once: there has to be snow on the roof, the upper part of the roof surface has to be above freezing, and the lower edge has to be below freezing. Heat escaping from the house warms the upper roof, snow melts, the water runs down to the cold eave and refreezes. Day after day, the ridge grows.
Do gutters cause ice dams?
No. Ice dams form on roofs with and without gutters, because the cause is uneven roof temperature. That is why the University of Minnesota Extension’s long-term advice focuses on the attic:
- Air sealing first: make the ceiling airtight so warm, moist air cannot flow from the house into the attic.
- Then insulation: more ceiling or roof insulation reduces heat loss by conduction.
- And ventilation: cool outside air should enter at the soffits and leave near the ridge. Insulation alone will not prevent ice dams, but together with ventilation it keeps the roof surface cold and even.
Gutters are not the cause, but they are often where the damage shows. A gutter full of ice is extremely heavy. It bends, pulls its fasteners out of the fascia and can rip off entirely. Ice can also build up inside the gutter and add to the dam at the roof edge.
Should you take your gutters down?
Removing gutters does not stop ice dams, and it brings back the problems gutters solve the rest of the year: roof water dumping at the foundation, splashing on siding and eroding beds. The better approach is to fix the attic and make sure the gutters can handle ice.
How to make gutters survive ice
Hangers and fasteners
Old spike-and-ferrule gutters are the ones that fail first. Spikes work loose over years of expansion and contraction, especially in soft or rotted fascia. Modern hidden hangers are screwed into the fascia and rafter tails. Angi’s hanger-spacing guide recommends no more than 3 feet between hangers in general, and about 2 feet apart where heavy snow and rain are common.
Sound fascia
Hangers are only as strong as the wood behind them. Soft or rotted fascia boards should be replaced before new gutters go up. On old New England and Midwest homes, this is often a bigger part of the job than the gutters themselves.
Drainage that does not freeze shut
Downspouts that end in a low spot or on a walkway can freeze solid, backing water up into the gutter. Discharge onto a slope that drains away from the house, and keep extensions off paths where refrozen water becomes a hazard. The City of Chicago makes the same point when it encourages homeowners to disconnect downspouts from the sewer: consider where the water goes, and remember that cold weather causes icing.
Correct placement
Gutters hung too high, right against the roof edge, catch sliding snow and ice. Installers set the gutter so the roof edge overhangs it properly. On metal roofs, which shed snow all at once, snow guards on the roof can protect the gutters below.
Do gutter guards help or hurt in winter?
A good guard keeps leaves out in fall, so the gutter enters winter empty and drains freely. That is a real benefit, because a gutter half-full of wet leaves freezes into a solid block. But guards also need to handle snow load. Look for guards that are fastened securely, sit in line with the roof so snow can slide off, and are rated for snow country. Flimsy drop-in screens can collapse or hold a layer of ice on top.
Roof-edge details that help
Two roofing details make ice dams less damaging, and they are worth checking whenever the roof or gutters are replaced. First, the drip edge: a metal flashing along the eave that directs water into the gutter instead of behind it. Second, an ice barrier: a self-adhering membrane under the shingles along the eaves. The International Residential Code requires an ice barrier in areas where there has been a history of ice forming along the eaves, extending from the edge of the roof to a point inside the exterior wall line. Neither prevents ice dams, but both help keep backed-up water out of the house when one forms.
Heat cables
Electric heat cables in gutters and along the roof edge can keep a channel open for meltwater. They treat the symptom, not the cause, use electricity, and must be installed according to the manufacturer’s instructions. They can make sense on a problem section while the attic is being fixed.
When ice has already damaged your gutters
Look for gutters that lean forward, hangers that have pulled out, seams that have split, and fascia that is stained or soft. If the damage is limited to one run, re-hanging or replacing that run may be enough. If gutters are pulling loose all around the house, plan a full replacement with hidden hangers in spring, and fix the attic before next winter. Our guide to signs you need new gutters helps you decide.
What to ask an installer in snow country
- What hanger type do you use, how far apart, and what do they fasten into?
- Will you check the fascia and rafter tails, and how is repair priced?
- How will the gutter sit relative to the roof edge and drip edge?
- Where will each downspout discharge, and will it freeze on a walkway?
- Is the guard you offer designed for snow load, and how is it fastened?
- What does the workmanship warranty cover if ice pulls a gutter loose?
Snow country at a glance
- Boston: record 110.6 inches of snow in the winter of 2014–15; old wood gutters and box gutters common
- Chicago: 36.7 inches of snow in a normal year (1991–2020), plus frequent freeze-thaw cycles
- Minneapolis–St. Paul, Buffalo and Denver: heavy snow loads and long winters
- Philadelphia and North Jersey: less snow, but ice on old, patched gutters is a common reason they pull loose