Ice dams form when heat escaping from your house melts the snow on your roof and the water refreezes at the colder edge. The Minnesota Department of Commerce calls warm air leaking into the attic the primary cause. University of Minnesota Extension says to take the snow off for now, then seal the attic air leaks and consider adding insulation to stop ice dams coming back.
What to do about ice dams, from University of Minnesota Extension:
- Now: get the snow off the roof.
- If water is coming in: channel it off.
- Then: seal attic air leaks.
- After that: consider more insulation.
What Is an Ice Dam?
A ridge of ice at the edge of a roof that stops melting snow from draining off. University of Minnesota Extension says the water backed up behind it can leak into your home and damage walls, ceilings and insulation.
Extension also says moisture from ice dams can lead to mold and mildew, which can cause breathing problems, so dry out anything wet straight away.
The air leaks behind ice dams do harm too. The Minnesota Department of Commerce says water vapor in warm air escaping into the attic can condense and freeze in the insulation. Wet insulation has little insulating value, and the water can crack plaster and paint and lead to rot.
What Causes Ice Dams?
Mostly heat from your house reaching the roof, Extension says, and in rare cases the sun. An ice dam needs snow on the roof while the upper roof is above 32°F and the lower edge is below it, on average over a sustained period, with the outside air below freezing. Snow melts on the warm part, runs down and freezes at the cold edge. The dam grows, and water pools behind it and finds its way in.
Often the heat comes from air leaks. Extension says that in many homes, warm air leaking into the attic is the main way heat reaches the roof. The Minnesota Department of Commerce calls attic air leaks the primary cause of ice dams. Heat reaches the attic and roof through:
- Gaps around plumbing vents, electrical wires and chimneys (Minnesota Department of Commerce)
- Gaps around unsealed can lights, ceiling fans, drop soffits and chimney chases (Focus on Energy)
- Unsealed ceiling light fixtures below an unheated attic (Minnesota Department of Commerce)
- Kitchen and bath fans that vent just above the roof, which Extension says may add to the melting
- Chimneys, especially with frequent wood stove or fireplace use, leaky or poorly insulated ducts in the attic, and knee wall spaces (Extension)
- Thin insulation at the top of the outside wall (Minnesota Department of Commerce)
How Do You Deal With an Ice Dam Now?
Take the snow off, or let the water out. University of Minnesota Extension says:
- Rake the snow off: Removing the snow takes away one of the things an ice dam needs. A roof rake and push broom can be used, but may damage roofing.
- In an emergency, make channels: If water is getting into the house, hose channels through the ice with tap water on a warm day. Work up from the lower edge of the dam.
- Expect it to be temporary: Extension says a channel stops working within days.
Extension warns that anyone on a roof in winter, or working on it from below, risks injury and may damage the roof and house, and says to contact professionals for the job.
What Shouldn’t You Do About Ice Dams?
Don’t chip, heat or vent your way out. The Minnesota Department of Commerce says to avoid:
- Heating cables: They shorten your roof’s life and cost money to run.
- Chipping, chemicals or heat to remove the ice: These can damage shingles and gutters.
- Extra roof vents, including powered ones: They will not eliminate ice dams and often make them worse.
Know the limits, too. More insulation helps, but insulation alone isn’t enough. University of Minnesota Extension says mechanical attic ventilation is not a recommended fix in Minnesota, as it can cause other attic moisture problems and unwanted negative pressure in the home.
You still need some attic ventilation. Extension says natural roof ventilation can help keep roof temperatures even, though once leaks are sealed and insulation added only a little is needed, and natural attic ventilation is needed to dry the attic and clear summer heat. The Commerce Home Energy Guide says that even after sealing air leaks, minimum attic ventilation is still required.
Some valley roofers name ice dams on their own websites: see the ice dam removal roofers. Ask whether they remove them, and how: Commerce warns that chipping, chemicals or heat can damage shingles and gutters.
How Do You Stop Ice Dams Coming Back?
Stop the heat getting into the attic. University of Minnesota Extension says to make the ceiling airtight first, so no warm, moist air flows into the attic. Then think about adding ceiling or roof insulation.
- Seal the leaks: The Minnesota Department of Commerce says foam spray or caulking can seal attic air leaks, saving energy and preventing nearly all ice dams. It says to disconnect power to a circuit until foam around its fixture cures.
- Seal the lights: Commerce says light fixtures below an unheated attic must be sealed tight, with airtight recessed cans or boxes sealed over them. An airtight box over a recessed light also reduces the fire hazard from insulation lying against it.
- Insulate the edge: Commerce says the top of the outside wall has little room for insulation, right where ice dams form. Spray foam there helps.
- Top up insulation: The Commerce Home Energy Guide says R-60 in a Minnesota attic can give a good barrier to heat loss; the code minimum for new buildings is R-49. Focus on Energy typically recommends R-49 or higher for Wisconsin attics, about 18 inches of fiberglass.
Extension says weatherization contractors deal with this kind of heat loss. The one you hire should run a blower door test to see how airtight your ceiling is, and may use an infrared camera to find where heat escapes. When a house is tightened up, Extension says, fans, exhausts and anything that burns fuel still need enough air to run safely.
Commerce also warns that old knob and tube wiring, or worn or broken wires, must be protected or replaced before insulating and sealing. Commerce says an insulating contractor can often reach the hard-to-insulate edge of the attic from inside with a spray wand, or through the soffit. If you’re re-roofing, it says roof boards can be removed to reach the hard-to-insulate edge of the attic from outside.
Focus on Energy, writing for Wisconsin homes, says it offers incentives for insulation and air sealing, and suggests an energy assessment as a first step.
Can Your Roof Hold the Extra Snow?
Usually, if it’s built to current codes. Extension says stopping the melt means more snow stays on the roof, but a house built to current codes should not have a structural problem. In Minnesota, plans showing the snow load design are usually needed for a building permit, and yours may be on file at your local building inspection office. A professional engineer can check how strong your roof is.
What About Water Damage Inside?
Wait until it dries, then fix it with the cause. Extension says not to repair ceilings and walls until they’re dry, and to do the inside repairs together with fixing the heat loss. Otherwise the damage will happen again.