Ice Dam Prevention and Repair in Trenton: Fix the Heat, Not Just the Ice

What actually causes an ice dam?

Heat escaping from the house warms the roof deck, melts snow lying on it, and the water refreezes where the roof is cold, at the eave. The ice builds into a dam that holds back later meltwater, which is forced under shingles. Insulation, air leaks and ventilation decide whether the roof is warm or cold.

It takes three things together: snow on the roof, heat reaching the underside of the deck and a cold edge. Remove any one of them and the dam does not form. You cannot control the snow, but you can control the heat.

That is why replacing shingles alone rarely stops ice dams. A new roof on an unchanged attic will have the same melt pattern.

Can I knock the ice off the eaves myself?

No. Chipping ice with a hammer or shovel damages shingles and risks falls from a ladder or roof, and falling ice can injure people below. Rock salt can corrode metal and harm plants. Use a roof rake from the ground to clear snow, and call a roofer for the ice.

A roof rake, used while standing on the ground, can pull snow off the lower few feet of a slope before it melts and refreezes. That reduces the supply of water, and it is a safe measure if you can do it without a ladder.

For an active leak, a roofer can open channels with methods that do not tear the roofing.

Why are rowhouses and older attics more prone to ice dams?

Many have thin or settled insulation, gaps where wiring and chimneys pass through the attic floor, and little ventilation. Heat leaks upward and warms the deck. In an attached row the roof space may also be shared with warm neighbors, which adds heat along the shared wall.

Houses built before modern insulation practices usually lose more heat through the ceiling, and years of renovation can leave holes in the ceiling plane where lights, ducts and vents were added.

Mid-century houses in the Bucks County and Mercer suburbs often have shallow attics with limited space for deep insulation or airflow, so the fix may involve careful design and not just adding more material.

Who fixes an ice dam problem: a roofer or an insulation contractor?

Usually both. The roofer deals with the ice, the eave damage and the vents, and can add waterproofing under the shingles on a re-roof. Air sealing and insulation are typically done by an insulation or energy contractor. A good roofer will tell you which jobs are theirs and which are not.

Ask the roofer to write down what they found in the attic and what they recommend. That gives you something to hand to an insulation contractor and a way to compare quotes.

For the background on how a heavy snow and a thaw interact, read the guide on ice dams and nor'easters in the Trenton area.

What can I do before winter to cut the risk of ice dams?

Keep gutters and downspouts clear, look at the attic for thin or disturbed insulation and light leaking around the hatch and fixtures, make sure soffit vents are open and ask a roofer to check the eaves. These steps reduce heat reaching the roof and give meltwater a clear path out.

Autumn is the time to act. Once the first heavy snow is on the roof, the options narrow to clearing and waiting. Look in the attic on a bright day: if you can see light around the hatch or recessed lights from the attic side, warm air is leaking upward, and that air carries the heat that melts the snow.

Check that insulation has not been pushed over the soffit openings at the eaves. A common mistake is stuffing insulation into the corner and blocking the intake, which stops cold air flowing under the deck. Cardboard or plastic baffles hold the insulation back and keep the channel open.

On a rowhouse, remember that your neighbor's attic is on the other side of the wall. You cannot change theirs, but sealing your own side and keeping your roof edge in good order protects you from most of the damage. If you are planning a re-roof, ask the roofer about an eave membrane and ventilation while the roof is open.