What Ice Dams Are
When heat escapes into the attic, it melts snow on the upper roof. Water runs down to the colder eaves, refreezes, and builds up into a dam. Subsequent meltwater pools behind the dam and backs up under shingles.
Why They Happen Here
Southern Maryland gets freeze-thaw cycles — snow, then a warm day, then freezing night. That cycling is ideal for ice dam formation, especially on poorly insulated or ventilated roofs.
Prevention
- Adequate attic insulation (keeps heat in living space)
- Proper ventilation (keeps roof deck cold)
- Ice and water shield membrane along eaves (last line of defense)
- Sealed attic air leaks (recessed lights, plumbing chases)
If You Have Them
Don't chip at ice — you'll damage shingles. Use calcium chloride in a nylon stocking laid across the dam (not rock salt). For severe cases, call a professional with steam equipment.