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Ice dams form when heat escaping from your attic melts snow on the upper portion of your roof. That meltwater flows down to the colder eaves, refreezes, and creates a dam that traps water — which then backs up under your shingles and leaks into your home. It's one of the most common and destructive winter roofing problems in Maryland and Delaware.
How Ice Dams Form
The process is simple physics: warm air from your living space rises into an poorly insulated or ventilated attic, heating the roof deck from below. Snow melts on the warm upper sections, runs down to the unheated eaves (which overhang beyond the exterior walls), and refreezes. As this cycle repeats, the ice dam grows, trapping standing water that finds its way under shingles.
Prevention Strategy 1: Proper Attic Insulation
The goal is to keep your attic cold — the same temperature as the outside air. This means adequate insulation on the attic floor (R-49 is recommended for our climate zone). Check for gaps around light fixtures, plumbing vents, and HVAC ducts where warm air commonly leaks into the attic space.
Prevention Strategy 2: Adequate Ventilation
Even with perfect insulation, some heat enters the attic. Proper ventilation exhausts it before it can warm the roof. The standard formula is 1 square foot of ventilation for every 150 square feet of attic space — balanced between intake (soffit vents) and exhaust (ridge vent). Make sure soffit vents aren't blocked by insulation.
Prevention Strategy 3: Ice and Water Shield
For new roofs or replacements, ice and water shield membrane along the eaves provides a critical backup. This self-sealing membrane is installed beneath shingles along the first 3-6 feet of the roof edge. Even if water backs up past the shingles, the membrane prevents it from reaching the decking.
What NOT to Do
Don't hack at ice dams with an axe or hammer — you'll damage your shingles and potentially your roof deck. Don't use rock salt on your roof (it corrodes metal and damages shingles). Roof heat cables can help in emergencies but they're an expensive band-aid that doesn't address the root cause.
When to Call a Professional
If you see icicles forming along your eaves, water stains on interior ceilings or walls near exterior walls, or ice buildup more than a few inches thick, call a professional. PCR can safely remove ice dams and, more importantly, identify and fix the underlying insulation and ventilation issues that cause them.