Ice Dams at the Cottage: What They Are and What To Do

What an ice dam actually is

An ice dam is a ridge of ice that builds up along the cold edge of a roof and traps water behind it. It looks like a solid band of ice — often with a curtain of icicles hanging off it — sitting right where the roof meets the eaves.

Here is how one forms, step by step:

• Heat escaping from the cottage into the attic warms the underside of the roof.
• Snow sitting against that warmer upper roof melts from below, even on a cold day.
• The meltwater trickles down the slope, under the blanket of snow.
• When it reaches the eaves and the overhang — which hang past the heated part of the cottage and stay at the outdoor temperature — it refreezes.
• Do that over and over, through a winter of thaws and cold snaps, and the refrozen water builds into a ridge of solid ice: the dam.

Once the dam is there, it does the real damage. Fresh meltwater running down the roof hits the ice and has nowhere to go, so it pools behind the dam. Shingles are built to shed water that runs off — they are not built to sit in a standing pool. Given a few days, that trapped water can work its way up under the shingles, through to the roof deck, and into the cottage below.

None of this needs a warm spell. A sunny afternoon a few degrees below freezing is enough to melt snow on a dark roof and start the cycle.

Why cottage roofs are prime candidates

We see ice dams every winter on the Bruce and around Georgian Bay, and cottages tend to get hit harder than the average year-round house. A few things stack up on cottages across the Ontario snowbelt:

• Uneven heating. A cottage warmed by one wood stove or a couple of space heaters ends up with warm patches and cold patches across the roof. Snow melts over the warm zones and refreezes over the cold ones — the exact recipe for a dam.
• Older, thinner insulation. A lot of cottages up here were built in another era, with attic insulation that is thin, patchy, or settled over the years. More heat reaches the roof deck, so more snow melts from below.
• Part-time heat cycling. This is the big one. A cottage that gets heated up for a weekend and then left to go cold runs through melt-then-freeze cycles all winter — and every cycle feeds the ice at the eaves.
• Deep lake-effect snowpack. The snowbelt piles it on. Lake-effect snow forms when cold air slides across the open, still-warmer water of Lake Huron and Georgian Bay, picks up moisture, and drops it on the downwind shore. That deep snow is both the raw material for a dam and a thick blanket that holds heat against the roof deck, melting the layer underneath faster.

Put those together and a quiet, part-time cottage in the snowbelt is close to a perfect ice-dam machine.

The warning signs to watch for

Ice dams announce themselves if you know where to look. On a winter visit, or from a photo a neighbour sends you, these are the tells:

• A thick curtain of icicles along the eaves and gutters. A few icicles are normal. A heavy, growing wall of them hanging off the roof edge means meltwater is refreezing there — and where there are icicles, there is often a dam behind them.
• Ice at the soffit vents or pushing out of the overhang. When you can see ice in or around the vents under the eaves, water is getting where it should not be.
• A solid band of ice along the roof edge. Not the icicles — the dam itself, a ledge of ice sitting on the eaves.
• Stains where the ceiling meets an outside wall. Inside, an ice dam usually shows up first as a damp patch or a brown stain along the top of an exterior wall or in a ceiling corner — the eaves side of the room. That is water that has already found its way in.

If you catch the outside signs early, there is time to get the snow off before water starts backing up. If the stain is already inside, the dam has been working for a while.

What not to try yourself

We understand the urge to grab a ladder and deal with it. Before you do, here is the honest risk in each of the do-it-yourself fixes people reach for:

• Raking or chipping from a ladder in winter. A ladder on frozen, uneven ground, with ice underfoot and sheets of snow ready to slide off the roof onto you, is one of the more dangerous places on a winter property. Falls from height are exactly the kind of accident this work is known for.
• Chipping the ice off with a tool. A hammer, hatchet, or chisel swung at a dam lands right where water is already sitting — and it is far too easy to drive the blade through a shingle or into the roof deck. You can turn a slow backup into an open hole.
• Throwing salt or ice-melt on the roof. Rock salt and cheap ice-melt pucks can pit and corrode shingles, flashing, and metal eavestroughs, and the salty runoff stains siding and can burn the plants underneath. It is a lot of damage for very little melt.

We are not telling you it is against the rules — it is your cottage. We are telling you what tends to go wrong, because we are the ones who get the call afterward.

If you do decide to knock some snow down, a roof rake used from the ground, on the low eaves only, is the safest tool there is. Never from a ladder, and never up on the roof itself.

What professional handling looks like

When you would rather not be on a ladder in January, that is our job. Clearing an ice dam is really two pieces of work:

• Taking the snow load off above the dam. The snow up-slope is what keeps feeding meltwater to the ice. We clear it back, so there is less snow sitting above the dam to melt down into it. Our technicians are trained for winter roof work and tie off in proper fall-arrest gear, and Cottage Hero is insured, so the risk of the job stays with us.
• Opening safe drainage through the ice. Rather than chipping at a dam and gouging the roof, the careful way to release the water trapped behind it is to melt a channel through the ice so the pool behind it can drain. It is slower than swinging an axe, and it is a great deal kinder to the roof.

We clear down to a safe margin above the roof surface rather than scraping it bare, to keep from chewing up the shingles. For the bigger picture on snow weight and when a roof needs clearing at all, we go deeper in our guide to how much snow a cottage roof can hold.

There is also a longer-term side to ice dams worth naming honestly. The reason snow melts from below in the first place is heat escaping into the attic — so the lasting fix most contractors point to is air-sealing and improving attic insulation, so less warmth reaches the underside of the roof. That is not work we do, and it is worth asking your contractor or an insulation company about if you are fighting dams year after year. What we handle is the winter side: getting the snow and ice off safely when it is already stacking up.

Getting the ice off, and eyes on the roof

Ice dams are a snowbelt fact of life from Sauble Beach and the South Bruce Peninsula down the Lake Huron shore and around Georgian Bay. On a cottage that sits cold and empty, the freeze-and-thaw cycles come and go all winter with no one there to see the ice building at the edge — which is why they so often turn into a ceiling stain nobody notices until spring.

Two of our services cover it. Our roof and deck snow removal takes the snow load off and opens drainage through a dam that has already formed, with a clear quote up front for your particular roof. And because an empty cottage can go weeks unseen, our winter checkups put someone at your place on a schedule, watching the eaves and the ceiling corners — so if a dam starts building, you hear about it fast, with photos and a plain explanation.

If you would rather talk it through, call us at 519-783-1575. The phone is answered 7 days a week. Tell us where your cottage is and how it is set up, and we will walk you through what the roof needs.