How an ice dam forms
- Snow covers the roof.
- Warm air from the living space leaks into the attic and warms the roof deck.
- Snow on the upper roof melts and runs down.
- At the eaves, which hang past the warm walls, the roof is cold, so the water refreezes.
- The ice builds into a ridge, and new meltwater pools behind it.
- The pooled water works its way under the shingles and leaks inside.
Signs you have an ice dam
- A thick ridge of ice along the roof edge or in the gutters
- Large icicles hanging from the gutters
- Water stains or peeling paint on ceilings near outside walls
- Damp insulation or frost in the attic
- Water running down inside walls or around window frames
Why they happen
Warm air leaks into the attic through gaps around light fixtures, attic hatches, plumbing stacks and bathroom fans.
Too little insulation lets heat from the house reach the roof deck.
Poor ventilation traps warm air in the attic instead of letting cold outside air keep the roof deck cold. Many older homes in Willingboro, Cherry Hill and Mount Laurel were built with little or no ridge venting.
Clogged gutters give ice a head start at the edge.
What to do if you have an ice dam now
- Don't chip the ice with a hammer or axe. You'll damage the shingles.
- Don't climb onto an icy roof.
- Use a roof rake from the ground to pull snow off the lower few feet of the roof, if you can do it safely.
- Put buckets and towels under active leaks and photograph the damage.
- Call a roofer if water is coming in. Our line is open 24/7 at (609) 516-1178. See emergency roof repair.
Sudden water damage from ice dams is sometimes covered by homeowners insurance. Check your policy and see our insurance claim help.
How to prevent ice dams for good
Leak barrier at the eaves. A self-adhering membrane like GAF StormGuard goes under the shingles along the roof edge and in the valleys. If water backs up, it hits a watertight layer instead of the wood. We install it on every roof replacement, as part of a complete GAF roofing system.
Balanced ventilation. Soffit intake vents along the bottom of the roof and a ridge vent at the top keep the roof deck cold and even. See attic ventilation.
Air sealing and insulation. Sealing gaps between the house and the attic and adding insulation stops heat from reaching the roof.
Clean gutters before winter. Add gutter guards on wooded lots.
Are heat cables worth it?
Heat cables can help on a problem spot, but they treat the symptom, not the cause, and they use electricity all winter. Fixing ventilation and adding leak barrier is the long-term solution.
Ice dams and older South Jersey homes
Older Cape Cods and bungalows in towns like Riverside, Palmyra, Collingswood and Haddon Township are especially prone to ice dams. Their finished upstairs rooms sit right under the roof, often with little insulation and no room for airflow, so heat goes straight into the roof deck. On these homes, the fix during a roof replacement often includes adding leak barrier higher up the roof than the code minimum, improving soffit and ridge venting where the framing allows, and sealing gaps at the attic knee walls. We look at all of this during the inspection and explain the options before you decide.
Get your roof checked before winter
The best time to prevent ice dams is in the fall. Our free roof inspection checks your attic ventilation, insulation, flashing and gutters, and shows you photos of what we find. Call (609) 516-1178.
By Stefano, Homcertin LLC · November 2026
Frequently asked questions
Are ice dams covered by insurance?
Sudden water damage caused by ice dams is often covered, but policies vary. Check yours and document the damage with photos.
Does a new roof stop ice dams?
A new roof with leak barrier at the eaves stops ice dams from causing leaks. Better ventilation and insulation stop them from forming.
Should I remove snow from my roof?
Only the lower few feet, from the ground with a roof rake. Never climb onto a snowy or icy roof.