Ice Dam Prevention

Every February a good share of Duluth is chipping ice off eaves and looking at a stain on a bedroom ceiling. There are signs stapled to telephone poles offering to take the ice off your roof, and in an emergency that is a service worth paying for.

But removal is not a fix. It is the same job again next winter, and the winter after that.

Ice dams are a heat problem. Once you see the mechanism, the permanent fix is obvious and it has nothing to do with your roof.

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What is actually happening

1. Warm air from your living space leaks into the attic. It goes through gaps around bath fans, recessed lights, plumbing stacks, wiring holes, the attic hatch, the chimney chase, and the top plates of every interior wall. In balloon framed houses it comes straight up the wall cavities from the basement.
2. That warm air heats the attic and the underside of the roof sheathing.
3. Snow on the roof melts from below, even at 10 degrees outside.
4. The meltwater runs down the roof until it passes the exterior wall line. From there out, over the soffit and the overhang, there is no heated house underneath. That section of roof is at outdoor temperature.
5. The water refreezes there. It builds. And the next round of meltwater ponds behind the ice, sits on the roof, and works its way back up under the shingles by capillary action.

Notice what is not in that list. Your gutters did not cause it. Your shingles did not cause it. A bad roof job did not cause it. Heat did.

That is also why the damage shows up where it does. The stain on the bedroom ceiling is usually a few feet in from the exterior wall, because that is where the water got back under the shingles and found a path.

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If you have an active leak right now

Deal with the water first. The ice can wait an hour.

• Move what is under it. Then get a bucket down.
• If the ceiling is bulging, poke a small hole at the low point. It feels wrong. It is right. Drywall holding a pocket of water will let go all at once, and a small hole you control drains it in one place.
• Get steam removal from someone who does it for a living. Steam is the only method that takes ice off asphalt shingles without taking granules with it.

What not to do, in order of how often we see the damage:

• Do not chip at it. Hatchets, hammers, and ice picks go through shingles. Now you have an ice dam and a roof leak in July.
• Do not use salt or standard ice melt. It damages shingles, kills whatever it drains onto, and corrodes gutters and flashing.
• Do not power wash it. Cold water on a cold roof makes more ice.
• Do not get on the roof. A pitched Duluth roof in February is how people get hurt.

Once the emergency is over, the actual question is why your house builds a dam and the one next door does not.

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Why the usual fixes disappoint

Heat cable melts a channel through the dam. It does not stop the dam forming and it runs on your electric bill all winter. It is a bandage on a roof you cannot fix any other way, and there are a few of those, but it is not a solution.

Raking the roof works and it is genuinely useful in a big snow year. It also means getting on a ladder in January, every time it snows.

Removal on a schedule is the one that quietly becomes permanent. If you are paying someone every winter, you are renting a fix at a price that would have bought the repair in about three years.

More insulation with no air sealing is the one that costs real money and disappoints people. Air moving through insulation carries far more heat than conduction through it does. Blowing another foot of cellulose over an unsealed attic floor slows the leak but does not stop it, and if the installer buries the soffit vents while they are at it, the attic gets warmer and the problem can get worse.

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What actually works

Seal every hole in the attic floor. Then insulate to depth. Then make sure cold outside air can move freely from the soffits, over the insulation, and out the ridge.

That sequence, done correctly, is the fix. It is not glamorous and it is mostly crawling around on your hands and knees with a foam gun finding leaks. That is the job.

The goal is a cold attic. An attic that is the same temperature as the air outside cannot melt the snow on your roof, and a roof that does not melt does not build a dam at the eave.

Where the leaks actually are, roughly in order of how much air they move:

• The attic hatch, if it is an uninsulated panel sitting in a frame
• Top plates of interior walls, which are open to the wall cavity below on most older houses
• The chimney chase and any plumbing stack penetration
• Bath fans, especially ones venting into the attic rather than through the roof
• Recessed lights, unless they are rated and gasketed
• Balloon framed wall cavities, which run uninterrupted from the basement to the attic and are the single biggest one when they are present

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What it costs

Air sealing the attic floor: $1,500 to $3,000 for a typical Duluth house. This is the part that stops ice dams.

Air sealing plus insulation to R-49: {{PRICE_ATTIC_R49}}. Minnesota code minimum for Climate Zone 7.

Air sealing plus insulation to R-60: {{PRICE_ATTIC_R60}}. The newer model energy code target, and the better number in this climate.

If your insulation is already at depth and the problem is purely leakage, the sealing alone may be the whole job. We will tell you that on the walkthrough rather than selling you insulation you do not need. See attic insulation for the full breakdown of assemblies and R-value targets.

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The roofs where this is harder

Not every ice dam is an attic floor problem, and it is worth saying so.

Cathedral ceilings and low slope sections over living space have no attic floor to seal. The fix there is usually foam against the underside of the roof deck, which is a different job with different economics.

Complicated roof geometry with valleys, dormers, and multiple planes gives meltwater more places to pool and refreeze. Sealing still helps, but the dam may not go away completely.

A roof at the end of its life should be replaced before or with the insulation work, not after. Ice and water shield along the eaves goes on during a reroof, and it is the belt to the air sealing suspenders.

If your house is one of these, you will hear that on the walkthrough. Sometimes the honest answer is that heat cable on one problem section plus sealing everywhere else is the right package.