What causes ice dams on an Ottawa roof?

Heat escaping into your attic. Natural Resources Canada puts it plainly: if the attic temperature is above freezing it warms the roof sheathing, which melts the layer of snow in direct contact with the roof. That meltwater runs down to the overhang, and if the air and the overhang are below freezing the water freezes there and starts the ice dam. Ottawa's winters supply the other half of the recipe — long stretches cold enough to keep the eaves frozen while the roof above stays warm.

Why does an ice dam cause a leak inside the house?

Because water backs up behind it. Natural Resources Canada describes the mechanism directly: as melting snow or rain runs down the roof it meets the ice mass and backs up, sometimes under the shingles and then leaking into the attic. The dam itself does no damage. The pond of standing water it holds above your shingle line is what finds its way inside, which is why a leak can appear during a thaw rather than during the storm.

Should I remove snow from my roof in Ottawa?

Sometimes, but it is a symptom fix and it is worth knowing that before you pay for it every winter. Clearing the snow removes the material an ice dam is built from, so it stops the immediate problem. It does not change why your roof was warm. If you are clearing the same roof every year, the money is better spent on the attic, and if you have an active leak, act now and fix the cause in the spring.

What actually stops ice dams for good?

Air sealing and insulation, in that order. Natural Resources Canada states that a well-sealed and insulated attic results in a cool roof and generally will also not have ice dams, and that the best prevention is to seal all attic air leaks and insulate thoroughly. Ventilation is the second line: for houses with peaked roofs and accessible attics it recommends a ratio of 1 to 300, meaning unobstructed vent area to insulated ceiling area. Note the order — venting a leaky, under-insulated attic moves warm air around rather than removing the heat.

Can I clear my own roof?

A roof rake used from the ground is the only part most homeowners should do themselves, and even that has limits — you are pulling weight downhill toward yourself, near the eaves, often onto an icy walkway. Getting onto a snow-covered pitched roof in an Ottawa winter, or attacking an ice dam with anything sharp, is where people get hurt and where shingles get destroyed. Chipping ice off a roof damages the exact surface that is supposed to keep water out, so a cheap fix in January becomes a roof repair in April.

Who does roof snow removal in Ottawa, a snow company or a roofer?

Usually a roofing company. Most residential snow removal companies in Ottawa sell seasonal driveway and walkway contracts, which is machinery on the ground and a different job from working at height on a shingled surface in winter. Roof snow and ice dam work sits closer to roofing, and the companies that offer it tend to be roofers filling their winter. Ask any company directly whether roof work is something they do rather than assuming a snow contract covers it.

Does a seasonal snow removal contract include the roof?

Almost never, and this is worth confirming rather than discovering during a thaw. A residential seasonal contract in Ottawa is normally the driveway, the walkway and the ridge the City plow leaves across your driveway entrance. Roof work is a separate service at a separate price. Read what the contract lists as included, and if the roof matters to you, ask before you sign.

Guide

Roof Snow Removal in Ottawa: Ice Dams, When It Is Worth Paying For, and the Fix That Lasts

Last reviewed September 2026.

If water is coming through your ceiling during a thaw, clear the roof and stop the leak. But the thing worth knowing before you pay for it a second winter is that the ice is a symptom and your attic is the cause. Natural Resources Canada is unambiguous about the fix, and it is not a person on your roof: “The best prevention for ice damming is to seal all attic air leaks and insulate thoroughly.”Every page in this market that stops at “call us” is published by someone selling the call.

How an ice dam actually forms

The mechanism is heat, not snow. Source for this section: Natural Resources Canada, Keeping the Heat In, Section 5: Roofs and attics, read 2026-09-01.

Warm air leaks out of your house into the attic. “If the attic temperature is above freezing, it warms the roof sheathing, which melts the layer of snow that is in direct contact with the roof.”
That meltwater runs down the slope, under the snow, to the overhang — the part of the roof with no heated room beneath it.
“If the air and the overhang are below freezing, the water freezes on the roof and starts the ice dam.” Each thaw feeds it and it grows uphill.
Then the damage. “As melting snow (or rain) runs down the roof, it meets this ice mass and backs up, sometimes under the shingles and then leaking into the attic.”

Two things follow from that sequence that are not obvious. The ice itself is not what leaks — the standing water held behind itis, which is why the ceiling stain often appears on a mild day rather than during the storm. And a roof that dams badly while the neighbour's does not is telling you something about your attic, not about the weather you both had.

The part the companies selling removal leave out

Clearing snow and steaming out a dam works. It removes the material the dam is built from and it stops an active leak, and if water is coming in right now that is exactly what you should buy. What it does not do is change why your roof was warm, which means the same roof dams again next winter and the winter after.

Natural Resources Canada puts the durable fix in one sentence: “A well-sealed and insulated attic results in a cool roof and generally will also not have ice dams.” Note which order the two halves come in. Sealing the air leaks comes first, insulation second, and ventilation is the third line rather than the first — venting a leaky, under-insulated attic mostly moves warm air around. Where venting does apply, the same source gives the rule of thumb: “Houses with peaked roofs and accessible attics are the easiest to vent by using the ratio of 1 to 300. This ratio refers to unobstructed vent area to the insulated ceiling area.”

So the honest advice for a recurring problem is: treat the emergency in January, and book the attic work for a month when nobody is on your roof in the dark.

When roof snow is worth acting on

This page publishes no snow-load number, and that is deliberate rather than an omission. Ottawa's design snow load is an engineering figure that depends on your roof's shape, slope and exposure, and the sources a homeowner can reach disagree with each other and quote different quantities under the same words. A number that looks authoritative and describes the wrong thing is worse than no number. What is worth watching for instead:

A visible ridge of ice at the eaves, or icicles that keep coming back. Icicles are pleasant to look at and are the outward sign of exactly the process described above.
Water stains on a ceiling or at the top of an exterior wall, especially during a thaw rather than during rain. That is the backed-up water, and it means the dam is already past the shingle line.
Snow melting off one part of your roof and not another. An uneven melt pattern is a heat map of your attic, and the bare patches are where warmth is escaping.
Deep, dense accumulation after a thaw-freeze cycle or a rain-on-snow event. Wet, refrozen snow weighs a great deal more than the same depth of fresh powder, and drifting piles it unevenly rather than in a neat layer. Flat and low-slope roofs, and the valleys where two slopes meet, hold the most.
Any sagging, or doors and windows that suddenly stick. This one is not a maintenance question. Get people out and call a professional.

Why this is the wrong job to do yourself

A roof rake used from the ground is the one part most homeowners should handle, and it has real limits: you are pulling weight downhill toward yourself, near the eaves, usually onto the walkway you have just cleared. Do the ground-level first metre or two of roof and stop there.

Climbing onto a snow-covered pitched roof in an Ottawa winter is how people get badly hurt, and chipping at an ice dam with an axe, a hammer or a shovel destroys the surface that is supposed to keep water out. A shingle is not designed to be struck while frozen. The January saving becomes an April roof repair, and the leak you were trying to stop gets a permanent path.

What to ask before anyone climbs up

What method, and what does it do to the shingles? Removing ice with heat is a different proposition from removing it with a tool. Ask what they use and what they are prepared to say about the roof surface afterwards.
Are you insured for work at height, and can I see it? Winter roof work is the definition of a job where this matters. Ask for the certificate rather than the reassurance.
Is this snow removal, dam removal, or both? They are separate jobs at separate prices. Clearing the snow above a dam that stays put solves less than it sounds like.
What do you think is causing it?A company that answers “your attic” is telling you the truth. One that only quotes a return visit next winter is selling a subscription to your symptom.

Snow contractor or roofer?

Usually a roofer, and this catches people out. The Ottawa snow removal companies listed here overwhelmingly sell seasonal driveway and walkway contracts — machinery at ground level, routes booked before winter, priced per season or per visit. That is a different trade from working at height on a frozen shingled surface, and a seasonal contract almost never includes your roof.

Roof snow and ice dam work sits closer to roofing, so Ottawa roofing companies are the more likely answer, and several of them offer it as winter work. If the real fix turns out to be the attic, that is insulation and air sealing rather than either one. Whoever you call, ask plainly whether roof work is something they do — do not assume a snow contract covers it.

For what driveway and walkway clearing actually costs in this city, who owns the ridge the City plow leaves, and the contractor licence to ask for, see our Ottawa snow removal cost guide.

Common questions

What causes ice dams on an Ottawa roof?: Heat escaping into your attic. Natural Resources Canada puts it plainly: if the attic temperature is above freezing it warms the roof sheathing, which melts the layer of snow in direct contact with the roof. That meltwater runs down to the overhang, and if the air and the overhang are below freezing the water freezes there and starts the ice dam. Ottawa's winters supply the other half of the recipe — long stretches cold enough to keep the eaves frozen while the roof above stays warm.
Why does an ice dam cause a leak inside the house?: Because water backs up behind it. Natural Resources Canada describes the mechanism directly: as melting snow or rain runs down the roof it meets the ice mass and backs up, sometimes under the shingles and then leaking into the attic. The dam itself does no damage. The pond of standing water it holds above your shingle line is what finds its way inside, which is why a leak can appear during a thaw rather than during the storm.
Should I remove snow from my roof in Ottawa?: Sometimes, but it is a symptom fix and it is worth knowing that before you pay for it every winter. Clearing the snow removes the material an ice dam is built from, so it stops the immediate problem. It does not change why your roof was warm. If you are clearing the same roof every year, the money is better spent on the attic, and if you have an active leak, act now and fix the cause in the spring.
What actually stops ice dams for good?: Air sealing and insulation, in that order. Natural Resources Canada states that a well-sealed and insulated attic results in a cool roof and generally will also not have ice dams, and that the best prevention is to seal all attic air leaks and insulate thoroughly. Ventilation is the second line: for houses with peaked roofs and accessible attics it recommends a ratio of 1 to 300, meaning unobstructed vent area to insulated ceiling area. Note the order — venting a leaky, under-insulated attic moves warm air around rather than removing the heat.
Can I clear my own roof?: A roof rake used from the ground is the only part most homeowners should do themselves, and even that has limits — you are pulling weight downhill toward yourself, near the eaves, often onto an icy walkway. Getting onto a snow-covered pitched roof in an Ottawa winter, or attacking an ice dam with anything sharp, is where people get hurt and where shingles get destroyed. Chipping ice off a roof damages the exact surface that is supposed to keep water out, so a cheap fix in January becomes a roof repair in April.
Who does roof snow removal in Ottawa, a snow company or a roofer?: Usually a roofing company. Most residential snow removal companies in Ottawa sell seasonal driveway and walkway contracts, which is machinery on the ground and a different job from working at height on a shingled surface in winter. Roof snow and ice dam work sits closer to roofing, and the companies that offer it tend to be roofers filling their winter. Ask any company directly whether roof work is something they do rather than assuming a snow contract covers it.
Does a seasonal snow removal contract include the roof?: Almost never, and this is worth confirming rather than discovering during a thaw. A residential seasonal contract in Ottawa is normally the driveway, the walkway and the ridge the City plow leaves across your driveway entrance. Roof work is a separate service at a separate price. Read what the contract lists as included, and if the roof matters to you, ask before you sign.

Ottawa roofing companies, with sourced ratings and the date last checked.

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