How ice dams form
Three ingredients: snow on the roof, warm attic air, and cold outside air. Heat escapes from the living space into the attic. The roof deck warms above freezing where insulation is thin or ventilation is poor. Snow melts on the warmed portion. The meltwater flows down the roof until it hits the cold roof edge (where there's no living space below), refreezes, and builds up as ice — the dam.
Water keeps melting above the dam. With nowhere to drain, it backs up under the shingles, finds gaps in the underlayment, and drips into the attic, soffits, and exterior walls.
Damage ice dams cause
- Wet attic insulation (loses R-value, must be replaced)
- Stained ceiling drywall in upper rooms
- Wood rot on roof sheathing and rafters
- Mold growth in the attic from sustained moisture
- Wet exterior wall cavities (rare but possible)
- Frozen gutters torn off the fascia
Repairing significant ice-dam damage in Plymouth typically runs $2,000–$10,000+ depending on extent.
Why ice dams happen in your specific home
If your Plymouth home gets ice dams every winter, the root cause is almost always one of:
Inadequate attic insulation
Code requires R-49 in Minnesota attics (typically 16 inches of blown cellulose or fiberglass). Many 1980s–90s homes have R-30 or less. Heat escapes; roof warms; ice dams form.
Inadequate attic ventilation
Code calls for 1 sq ft of net free vent area per 150 sq ft of attic floor, balanced between intake (soffits) and exhaust (ridge or gable vents). Blocked soffit vents from blown insulation are the #1 culprit.
Air leaks from living space to attic
Recessed lights, bath fans, attic access hatches, and plumbing penetrations all let warm humid air into the attic. That air carries heat (warming the roof) and moisture (driving condensation).
How to actually fix ice dams
Heated cables on the eaves are a Band-Aid. The real solution is in the attic:
- Air-seal all penetrations from living space to attic
- Bring insulation up to R-49 with even coverage to the perimeter
- Install soffit vent baffles to keep the soffit pathway clear
- Verify balanced intake and exhaust ventilation
Done correctly, this eliminates ice dams permanently. Thermal imaging identifies exactly where insulation gaps and air leaks exist before you spend money.