An icicle is a spike of ice hanging from the roof edge. An ice dam is a thick ridge of ice along the eave that holds meltwater back on the roof. Icicles on their own are not an ice dam, but large ones can be a sign that one is starting, and a dam can sit behind the edge with few icicles to show for it.
Ice dam vs icicles: what each one actually is
The two are linked, which is why they get confused. Snow on the roof melts, the water runs down toward the eave, and some of it freezes there. National Research Council Canada describes it this way: water that is held back at the edge freezes into a dam, and water that cannot be held drips off and forms icicles.
- Icicles are hanging spikes of ice. They show that water is dripping over the edge.
- An ice dam is a ridge of ice built up in layers along the lower edge of the roof, sometimes reaching into the eavestrough. It blocks meltwater from leaving the roof.
The ridge is what causes trouble. Water backed up behind it can find its way under shingles or roofing laps and into the ceiling and walls. A fringe of icicles alone does not do that, though heavy ones can fall and hurt someone or damage what is below.
Do ice dams always have icicles? Can you have a dam without them?
No to the first question, yes to the second. Icicles form where water spills over an edge. An ice dam can build with few or none when:
- the eavestrough has filled with ice. National Research Council Canada notes that a gutter can stop icicles forming at first, until the ice fills it and icicles start at its lip;
- the dam sits partly up the roof, and the water is backing up behind it and soaking in rather than dripping over the edge.
The reverse is also true. You can have a row of icicles and no dam. It happens when a sunny afternoon melts some snow and the water drips off a bare, clear eave without building a ridge. Treat icicles as a possible warning, not proof. The Insurance Bureau of Canada says large icicles may indicate an ice dam or at least the start of one.
How to tell if you have an ice dam: checks from the ground
Do all of this from the ground, with binoculars or the zoom on your phone if you like. Do not put a ladder against iced eaves or walk on the roof.
- Look for a ridge, not just spikes. A dam is a lumpy band of ice along the eave, often several layers thick, that may extend up the roof past the edge. Icicles usually hang from it.
- Check the snow. Dams form when snow covers the roof right down to the eave. National Research Council Canada notes that when the snow stops short of the eave, a dam does not usually form, and the water runs onto the bare roof or makes only a thin layer of ice.
- Look at valleys and lower roofs. Where two roof slopes meet, meltwater collects and large dams can form at the lower end.
- Look on the walls. Wet streaks or ice on the siding below the eave suggest water has been spilling over or backing up.
- Check inside. Stains, bubbling paint or drips on ceilings near exterior walls, or damp at the top of an exterior wall, point to water coming in at the eave.
- Check the attic hatch. The Insurance Bureau of Canada suggests looking in the attic for frost. Look from the hatch only, in daylight, and do not step off the joists or onto insulation.
If you tick several of these, treat it as an ice dam. Our post on how ice dams form on Ontario roofs explains the cycle behind them.
Ice dam vs frozen gutter
A frozen eavestrough is ice packed in the trough or downspout, with water spilling over the outer edge. Once the ice fills the gutter, icicles form at its lip. The roof above it may be clear. An ice dam is a ridge that rides up onto the roof above the gutter line.
The two feed each other. A gutter blocked with ice leaves water no place to go, and the ice can grow into a dam. A dam often takes in the gutter as well. If the ice is mainly in the trough and downspout, our post on eavestrough ice buildup on Ontario homes goes through the causes. If the ice reaches well up the shingles or panels, think dam.
Ice dam vs roof leak: which one is wetting my ceiling?
Both can leave a stain. The pattern is what helps you tell them apart. These are typical, not absolute.
| Check | Ice dam | Ordinary roof leak |
|---|---|---|
| When it appears | During a thaw after snow, with cold nights | Often during rain, or at any time of year |
| Where the stain is | Near the exterior wall, below the eave | Under a chimney, vent, valley or other roof feature, often well inside the house |
| What you see outside | A ridge of ice at the eave | No ice ridge is needed |
| When it stops | When the ice melts or the supply of meltwater ends | It returns with the next rain |
If you cannot tell, treat it as urgent anyway. Water in ceilings and walls can lead to damage and to mould and mildew, as the Insurance Bureau of Canada points out.
What to do once you know which you have
Icicles only: keep people and parked cars away from beneath them, and look again after the next thaw. Large or fast-growing icicles are worth watching.
A frozen gutter: do not work on it from a ladder on icy ground. Have it looked at, because ice that fills a gutter can build into a dam.
An ice dam: do not hack at it. Natural Resources Canada warns that attacking ice dams with an axe or ice pick will damage the roof surface. A roof rake used from the ground can lower the load of snow above the eave; see our post on when to use a roof rake.
Water inside: move belongings, take photos, and contact your insurer right away, as the Insurance Bureau of Canada advises. Then call someone to deal with the ice. D&D Snow Services does ice dam removal with low-pressure steam, which cuts channels in the ice without hammering or chipping.
The long-term fix is on the inside of the house. Natural Resources Canada says to prevent ice damming, seal all attic air leaks and insulate thoroughly.
Ice dam and icicle questions homeowners ask
Can you have ice dams without icicles?
Yes. An ice dam is a ridge at the eave, and icicles only appear where water spills over an edge. If the gutter is full of ice, or the water is backing up under the roof covering rather than dripping off, a dam can form with few icicles. Check for stains and ice on the siding.
Do icicles mean I have an ice dam?
Not necessarily. A sunny day can melt snow and drip water off a clear eave. But the Insurance Bureau of Canada says large icicles may indicate an ice dam or the start of one. Look for a thick ridge of ice along the eave, and for stains inside.
How do I know if I have ice dams?
Look from the ground for a thick, lumpy ridge of ice along the eave with snow above it, icicles hanging from it, and wet streaks on the siding. Inside, look for ceiling stains or drips near exterior walls. Several signs together mean an ice dam.
Is a frozen gutter the same as an ice dam?
No. A frozen gutter is ice packed in the eavestrough or downspout, with icicles at the gutter lip. An ice dam is a ridge that builds up onto the roof above the gutter. They often occur together, and a blocked gutter can help a dam to grow.
Is an ice dam the same as a roof leak?
No, though both can stain a ceiling. A dam leaks during a thaw after snow, near an exterior wall, with ice at the eave. An ordinary roof leak often shows up in rain and sits under a chimney, vent or valley. If you are unsure, treat it as urgent.
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Get a Free Snow QuoteKey Takeaways
- Icicles are spikes of ice where water drips off the edge. An ice dam is a ridge of ice that holds meltwater back on the roof.
- You can have icicles without a dam, and a dam with few icicles, so check for the ridge and for water inside.
- Make checks from the ground only. Look for a ridge, snow above it, wet siding, and stains near exterior walls.
- A frozen gutter has ice in the trough and downspout. A dam rides up onto the roof above the gutter.
- Do not chip or hammer an ice dam. Call your insurer if water is inside, and fix attic insulation and air leaks long term.
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