What an ice dam is and why Calgary gets so many
An ice dam is a ridge of ice that builds along the lower edge of a roof and traps meltwater behind it. It starts inside the house: heat escapes into the attic, warms the roof deck, and melts the underside of the snow sitting on the upper roof. That water runs downhill until it reaches the overhang, which sits outside the heated walls and stays cold. There it refreezes, layer after layer, until the ice is thick enough to hold back a pool of water.
Calgary adds a twist that most cold cities do not have. Chinooks can push the city above freezing, sometimes past 10°C, for days in the middle of winter, then the cold returns overnight. Each swing melts a load of snow at once and then locks the runoff into ice at the eaves. A single winter can bring many of these melt-freeze cycles, so a dam that looked minor in December can be a solid wall of ice by March.
Some roofs are more prone than others:
- Older homes with shallow attics and little room for insulation at the roof edge.
- Complex roof lines, where valleys collect snow and funnel water into one spot.
- Low-slope sections, dormers and storey-and-a-half homes, where water moves slowly or living space sits under the roof slope.
Signs you have an ice dam
The clearest sign is a thick band of ice along the roof edge with water or slush sitting just above it. Other clues are easy to spot from the ground or inside the house:
- Large icicles hanging along long runs of the roof edge, not just the odd one by the front door.
- Ice building on the drip edge or oozing down the siding below the eaves.
- Water stains or drips on ceilings and exterior walls near the eaves, often in upstairs rooms or closets, appearing in winter rather than after rain.
- Peeling paint or damp drywall at the top of exterior walls.
- Frost, damp wood or wet insulation in the attic, especially near the lower edge of the roof.
- Bare stripes in the snow on the upper roof while the lower roof stays snow-covered, a sign of heat loss.
Is it an emergency?
If water is actively coming through a ceiling, running inside a wall or dripping from a light fixture, treat it as urgent and call. Meltwater behind an ice dam does not drain on its own, and every warm afternoon pushes more of it into the roof deck, insulation and wall cavities. Inside, catch drips with buckets, move valuables away and switch off power to any fixture with water around it.
If you only see ice and icicles with no water inside, it is still worth booking a look soon, before the next chinook starts the melt again.
How ice dams are removed safely
Safe ice dam removal uses low-pressure steam, not force. Steam melts through the ice slowly and lets a roofer cut drainage channels so the trapped water can run off the roof. It softens the ice without hitting the shingles hard enough to crack them, knock off granules or break the seal between courses.
A typical removal follows a practical order:
- Assess from the ground and the attic. Where is the water getting in, how thick is the ice, and how much snow is loading the roof?
- Clear snow from the lower roof. Taking weight and future meltwater off the eaves helps stop the dam from rebuilding. Larger snow loads are a job for roof snow removal.
- Steam channels through the dam. Channels are opened at intervals so pooled water drains first, easing the pressure on the shingles.
- Remove the ice in sections. The remaining ice is melted back from the roof edge, working with the shingles rather than against them.
- Check for damage. Lifted shingles, bent drip edge and wet decking are noted so they can be repaired.
Methods that damage roofs
High-pressure washers drive water under shingles and strip their granules. Chipping and hammering crack shingles and tear the underlayment. A roof “cleared” these ways often leaks worse the next winter.
Why removal alone doesn’t fix the problem
Removing the ice stops today’s leak, but if nothing changes in the attic the dam usually comes back with the next snowfall and chinook. The ice is a symptom; the cause is uneven roof temperature. The usual culprits are:
- Attic air leaks. Warm, moist air rises through gaps around attic hatches, plumbing stacks, wiring holes and top plates.
- Thin or uneven insulation, especially at the roof edge where there is little space above the walls.
- Blocked or unbalanced ventilation. Intake vents at the eaves covered by insulation, or too little exhaust at the ridge, trap warm air under the deck.
- Heat sources in the attic. Older pot lights, and bath or kitchen fans that dump warm air into the attic instead of outdoors.
- Complex roof shapes. Valleys, dormers and roof-to-wall joints gather snow and concentrate runoff.
Long-term ice dam prevention
The lasting fix is a roof deck that stays cold from ridge to eaves, backed up by membrane in the spots where ice forms. Most homes need a combination of these:
- Ice-and-water shield at the next re-roof. This self-adhering membrane goes down along the eaves and in the valleys and seals around nails, so water held by ice has a much harder time reaching the deck. On Calgary roofs, ice damming and freeze-thaw make it a basic part of any proper roof.
- Balanced ventilation. Cold air should enter through intake vents at the eaves and leave at the ridge, carrying away heat and moisture. See roof ventilation for how that balance is set up.
- Air sealing and insulation. Closing attic air leaks and topping up insulation keeps house heat where it belongs. An energy or insulation specialist can assess this part of the house.
- Roof snow management. Pulling heavy snow off the lower roof before a chinook limits how much water the eaves have to handle. Our roof snow removal page covers when that makes sense.
- Heat cables, used with care. They keep drainage paths open on a stubborn section, but they use power all winter, cover only a narrow strip and do nothing about heat loss. Think of them as a band-aid for a spot that cannot be fixed another way.
Ice dam damage we repair
Once the ice is gone, the roof edge often needs work. We repair the roofing damage that ice dams leave behind:
- Lifted, cracked or torn shingles along the eaves, where ice expanded under the laps.
- Bent or loose drip edge pulled away by the weight of ice.
- Wet or rotted sheathing at the lower edge of the roof, replaced so new shingles have solid backing.
- Leaks in valleys, where runoff from two slopes meets an ice dam.
- Leaks around chimneys, where ice and water sit against the flashing. Failing metal there is handled through chimney flashing repair.
- Leaks around skylights in the lower roof, where ice builds on the uphill side of the frame.
Calgary timing for ice dam work
Removal happens when the ice is there; repairs and prevention are best planned around the calendar.
What affects the cost of ice dam removal
The cost of ice dam removal depends on how much ice there is and how hard it is to reach safely. The main factors are:
- Roof height and pitch. Two-storey homes and steep roofs need more setup and fall protection.
- Length of eaves affected. A dam along one short overhang is a smaller job than ice wrapping the whole house.
- Ice thickness. Thick, layered ice from weeks of melt-freeze cycles takes longer to steam through.
- Access. Tight side yards, fences, decks and landscaping change how equipment reaches the roof.
- Snow load. Heavy snow on the lower roof may need to come off before the ice can be treated.
If ice is building on your roof or water is showing up inside, book a free inspection or contact us and we will help you deal with today’s ice and plan how to stop it next winter.