Published August 29, 2026
Every January the same call comes in: top-floor units in a Twin Cities building reporting ceiling stains along an exterior wall. That is an ice dam, and it is an attic problem wearing a roof costume.
What actually causes it
Heat escapes from the building into the attic. Snow on the warm part of the roof melts, runs down to the cold eave, and refreezes into a ridge of ice. Water backs up behind that ridge and moves under the shingles, which are designed to shed water, not hold it back.
Three drivers, in order of importance:
- Air leakage into the attic — top-plate gaps, can lights, bath fans venting into the attic, open chases
- Insufficient insulation — under R-49 in most older metro buildings
- Poor ventilation — blocked soffit vents, inadequate ridge venting
Roof material does not cause ice dams. Heat does.
Emergency response — what to do this week
- Steam, do not chip. Hire steam removal. Hammers, picks, and chisels destroy shingles and create next year's leak.
- Never use salt or ice melt on the roof. It corrodes flashing and fasteners and stains siding.
- Clear snow from the lower three to four feet of roof with a roof rake from the ground where safe.
- Inside: contain the ceiling drip, relieve a bulging ceiling into a bucket, protect contents, photograph everything.
- Document the date and unit — repeat units point to a specific attic defect.
Ending the cycle
| Fix | Typical cost | Effect |
|---|---|---|
| Air sealing attic penetrations | $1,200–$4,500 | Largest single effect |
| Insulation top-up to R-49/R-60 | $2,000–$8,000 | Big; do after air sealing |
| Soffit baffles / vent correction | $900–$3,500 | Restores cold roof |
| Bath fan venting corrected to exterior | $350–$900 per fan | Common hidden cause |
| Ice and water shield at eaves (during reroof) | Included in reroof | Protects when a dam forms anyway |
| Heat cable | $12–$25 / ft installed | Band-aid; use only where geometry makes dams unavoidable |
Air seal first. Insulating over unsealed penetrations traps the problem.
Multifamily specifics
- Common attics in older buildings let heat from one unit dam the roof above another. Fixing one unit does not fix the roof.
- Corridor and stair pressurization pushes warm air upward — check the top of stairwells.
- Long low-slope sections and valleys dam first; prioritize inspection there.
- Repeat-leak units should be tracked by unit number across seasons. Three winters of the same unit is a defect, not weather.
Insurance note
Ice dam damage is generally covered by Minnesota property policies as sudden water damage, while the underlying insulation and ventilation deficiency is maintenance and is not. Document the event and the interior damage carefully, and expect the carrier to pay for repair, not improvement.
Fix it before next winter
We do attic air sealing, insulation, ventilation correction, roofing, and interior ceiling repair for Twin Cities apartment buildings — and we take January emergency calls.
Licensed MN remodeler QC807391. Call 612-400-8036.
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Frequently asked questions
What causes ice dams on apartment buildings?
Heat escaping into the attic melts roof snow that refreezes at the cold eave. Air leakage is the biggest driver, followed by insufficient insulation and blocked ventilation.
How do you remove an ice dam safely?
Steam removal only. Chipping with hammers or picks destroys shingles, and salt or ice melt corrodes flashing and stains siding.
Does insurance cover ice dam damage in Minnesota?
Interior water damage from an ice dam is generally covered as sudden water damage, but the underlying insulation and ventilation deficiency is treated as maintenance and is not.