Seasonal

Ice Dam Prevention: Why Ice Dams Form and What Stops Them

By Des Moines Roof Repair · October 28, 2026 · 8 min read

Ice dams in Des Moines show up the week after the first real snow, and the story is nearly always the same: three feet of icicles off the north eave, a wet spot on the ceiling by an exterior wall, and a homeowner on a ladder with a hammer. Des Moines averages about 35 inches of snow a season, most of it arriving in storms that sit on the roof for days at 20°F. That is exactly the recipe.

Here is what is happening up there, and why real ice dam prevention starts in the attic rather than on the roof.

Why ice dams in Des Moines start at the melt line

An ice dam is not a roof problem. It is a heat problem that shows up on the roof.

Warm air leaks out of your living space into the attic — around can lights, the attic hatch, the bath fan, the top plates of interior walls, the chimney chase. That warm air heats the underside of the roof deck. Snow on the heated part of the deck melts, even at 15°F outside. The water runs down under the snowpack until it crosses the eave, where there is no heated living space below — just soffit and outside air. There it refreezes.

Do that for three days and you have a ridge of ice an inch or two thick at the eave. The next melt water hits that ridge and ponds behind it. Standing water finds the seams between shingles, which are designed to shed running water, not hold back a pond. It runs backward under the shingles, through the nail holes, onto the deck, and down the wall.

That is why the stain is almost always on the ceiling right at the outside wall, and why it happens on the north and east slopes first — those get the least February sun to clear the snow.

Ice dam prevention: the three fixes that work, in order

Do them in that order. Insulation without air sealing is a screen door on a submarine — air moves through fiberglass freely, and blowing another foot of cellulose over unsealed can lights just hides the leaks. Ventilation without the first two moves a lot of cold air past a deck that is still being heated from below.

On a 1950s Urbandale ranch with an open attic, all three together run $2,500–$5,000 and end the problem permanently. On a 1920s Beaverdale bungalow with a finished half-story and knee walls, it is harder and costs more, because the heat is leaking into a cavity you can't crawl through.

What does not work

• Chopping the ice with a hammer or a hatchet. You will take the shingles and the drip edge with it, and the repair costs more than the removal.
• Salt pucks and pantyhose full of ice melt. They melt a channel through the dam that refreezes in a day, and calcium chloride running down the roof shortens the life of the shingles and stains the siding.
• Heat cable alone. A zigzag cable at the eave keeps a drainage channel open. It does nothing about the ice above it, it costs $150–$300 a winter to run, and plenty of houses with cables installed still get a dam above them. Treat it as a bandage on a house that is genuinely hard to fix.
• Tearing off the roof. New shingles over a hot attic dam up exactly like the old ones. Ice-and-water membrane at the eaves protects the deck when water backs up, which is why cold-climate building codes generally call for it (check with your city's building department for the local rule), but it does not stop ice from forming.

When there's already a dam on the roof

Ask for steam removal before you do anything else. A low-pressure steamer melts the ice off without touching the shingles. For ice dam roof repair, Des Moines quotes run roughly $400–$1,000 for a typical removal, more if the crew has to work a second story in the dark. Pressure washers and heat guns are not the same thing, and a company that shows up with either should be sent home.

Once the ice is off, the interior damage gets assessed: wet insulation has to come out, drywall that stayed wet more than 48 hours usually comes out too, and the deck gets checked from inside. The ice dam repair page walks through what that visit looks like, and the cost page has the removal and repair numbers side by side.

The one-hour check you can do this weekend

Before the snow flies, go into the attic on a cold morning with a flashlight:

1. Look at the underside of the deck for dark staining or frost — that's condensation from air leaking up.
2. Look for daylight or gray-stained insulation around can lights, the hatch and pipe penetrations. Gray means air is moving through.
3. Check that the insulation isn't stuffed into the soffit bays. It should stop at a baffle, with a clear air path from soffit to ridge.
4. Follow the bath fan duct. If it dumps into the attic instead of out the roof or wall, that's a shower's worth of moisture a day landing on your deck.

Anything you find on that list is cheaper to fix in November than in February. If you'd rather have someone else look, a roof inspection includes the attic, and our guide on when a roof leak is actually a condensation problem covers the cousin of this problem — the leak that has no hole above it at all.

Mistakes after the ice is gone

Once the dam melts and the drip stops, it is tempting to call it fixed. These are the common ways that goes wrong:

• Painting the ceiling first. If the attic is still leaking heat, the stain comes back next February. Fix the cause, let the drywall dry, then paint.
• Leaving wet insulation in place. Soaked insulation stops insulating and holds water against the drywall. It needs to come out and be replaced.
• Assuming a new roof solves it. New shingles over the same warm attic form the same dam. Membrane limits the damage; it doesn't stop the ice.
• Ignoring the bath fan. A fan that dumps into the attic adds moisture all winter. It is one of the cheapest fixes on the list.
• Doing one fix and stopping. Insulation without air sealing, or vents without either, usually leaves the problem in place.

Questions to ask before you hire help

• Will you remove the ice with steam, and what will you do if you find damage underneath?
• Will you go into the attic and show me where the warm air is getting out?
• Who does the air sealing and insulation, you or another trade?
• Is the price for the removal only, or does it include the interior and attic work?
• What should I check myself before the next snow?

A written answer to each one makes quotes easy to compare. If one company only offers to knock the ice off, and another explains the attic, you know which visit is worth more.

Common questions

Do heat cables stop ice dams?

Not on their own. A heat cable keeps a narrow drainage channel open along the eave, but the attic heat that melts the snow higher up is still there, so ice can still build above the cable. Cables make sense on a section that is genuinely hard to air-seal, such as a low-slope porch tie-in, not as the main fix.

Is ice dam damage covered by insurance in Iowa?

It depends on your policy, and the answer differs between carriers. Many homeowners policies treat sudden interior water damage from an ice dam differently from the cost of removing the ice or fixing the attic that caused it. Check with your insurer or agent before you file, and take photos of the ice and the interior damage first.

Why do ice dams form on some houses and not others?

The difference is almost always in the attic. Two houses on the same street get the same snow, but the one with leaky can lights, an unsealed attic hatch and insulation blocking the soffits heats its roof deck from below. North and east slopes, finished half-stories and knee-wall attics are the usual trouble spots.

When is the best time to fix the attic?

Fall, before the first real snow, when the attic is cool enough to work in and there's no ice on the roof yet. The work is the same in February, but by then the dam may already have pushed water into the walls and ceiling.