Ice Dams in Warren County, NJ: Why They Form and What Actually Stops Them

What exactly is an ice dam?

An ice dam is a ridge of ice at the eave that blocks meltwater from draining. Snow melts higher up where the roof is warm, runs down and freezes at the cold overhang. The ridge grows, water pools behind it and finds a way under the shingles and into the house.

Icicles are the part you see. They are a sign that water is flowing and freezing at the edge, and they are not the same as a dam. The dam is the ice mass at the eave, and the damage happens behind it, where standing water presses up against the shingles and seeps through nail holes and laps.

It is easy to blame the gutters, because that is where the ice sits. But a roof with perfect gutters can still build a dam, and a roof with no gutters can too. The ice forms where the warm roof meets the cold overhang, and gutters only happen to be there.

Why do ice dams form in Warren County?

Because the county has the two ingredients: snow that stays on roofs and cold nights followed by milder days. About 30 to 40 inches of snow fall in a year, and the temperature cycles above and below freezing. A house that leaks heat into its attic supplies the third ingredient.

The numbers come from the Warren County statistics page, which cites the New Jersey State Climatologist for about 45 inches of precipitation and 30 to 40 inches of snow a year. Aggregator pages put Washington at roughly 51 inches of precipitation and 30 inches of snow, so treat any single figure as approximate.

What turns snow into ice dams is heat. Warm air from living spaces leaks into the attic through the ceiling plane: around the hatch, recessed lights, plumbing stacks and chimney chases. Thin insulation lets more heat through. That heat warms the roof deck from below, and the snow above it melts from the underside while the eaves, which hang past the warm wall, stay cold.

What does New Jersey's ice-barrier bulletin say?

NJ Bulletin 07-3 limits the ice-barrier membrane requirement to areas where the January mean temperature is 25 F or less, which the bulletin says is Sussex County only. It dates from 2007 and was revised in 2015, so confirm the current edition. It does not make the membrane required in Warren County.

An ice barrier is a waterproof membrane laid over the deck at the eaves, under the shingles. It does not stop ice from forming. It stops meltwater that is pushed up under the shingles from reaching the deck and the house.

Because the rule is limited, a roofer who recommends a membrane at your eaves is following good practice in a snowy county, not meeting a legal requirement. That is a legitimate choice, and you can weigh it against the cost. Do not let anyone tell you that the state requires it for Warren County without showing you the text.

Check the current version of the bulletin and ask your municipal construction office how it applies at your address. The page on asphalt shingle roofing explains where the membrane sits in the roof.

How do I stop ice dams for good?

Stop heat reaching the roof. Seal the air leaks from the house into the attic, add insulation to the right depth and make sure soffit and ridge vents move air under the roof deck. Those three steps keep the roof cold, so snow does not melt from below and ice has no reason to form.

Air sealing comes first, because insulation over a leaky ceiling does little. The usual leaks are the attic hatch, recessed lights, bath and kitchen fan ducts, plumbing stacks, wiring holes and the gap around the chimney. Sealing them is a specialist job, and it is sometimes done by an insulation or energy contractor rather than a roofer.

Insulation comes second. More of it slows the heat that does get through. Ventilation is third: air entering at the soffits and leaving at the ridge sweeps heat and moisture from beneath the deck. The roofer should check that insulation does not block the soffit vents, which is a common mistake.

The service pages on attic ventilation and ice dam removal and prevention set out what a visit involves.

How is ice removed safely?

By a roofer who cuts channels in the ice so meltwater can drain, or removes the dam in sections with proper tools and fall protection. Chipping with a hammer or shovel damages shingles and gutters and is dangerous. From the ground, a roof rake can remove snow from the lowest edge.

Removal treats the symptom. It buys time while you fix the attic, and it may be urgent if water is entering the house. A roofer decides what is safe on the day, and if conditions are too dangerous, they may suggest a tarp or interior protection first.

Salt and de-icing products are sold for the purpose. Some help a little, and some stain or damage roofing, so ask a roofer before you try one. Heating cables are a partial measure at best, because they open a channel but do not stop the cause.

Expect the roofer to explain what was done and what was not. Cutting channels leaves the dam in place but lets water out, so the problem can return after the next snowfall unless the attic is dealt with. A good visit ends with a short written plan: what was removed, what caused the ice and what should be done before next winter.

• Stay off an icy roof
• Rake only from the ground
• Do not chip at the ice
• Move belongings away from wet ceilings
• Photograph the damage for your insurer

Does my house's age make it more likely?

Often, because older houses tend to have leakier ceilings and thinner insulation. In ZIP 07882, 1,572 of 6,233 housing units date from 1939 or earlier, per a Census-based profile, so many local houses were built before modern air sealing. Age is a tendency, not a rule, and later work may have fixed it.

Balloon framing, plaster ceilings, chimney chases and old wiring penetrations can all give warm air a path into the attic. A house that has been re-roofed and re-insulated may have corrected some of that, but changes can also block vents.

A roofer who inspects the attic will tell you what your house is doing. The service page on roof inspection explains what that looks like.

What can I check in my own attic before winter?

On a dry day, look from the hatch with a flashlight for insulation that is thin, compressed or pushed against the eaves, daylight at the roof edges, bath fans venting into the attic, and gaps around the chimney and plumbing pipes. Step only on the joists, and stop if anything looks unsafe.

Autumn is the time to look, because winter is when the problem shows. A line of frost on the underside of the roof boards on a cold morning, melting as the day warms, is a clear sign that warm moist air is reaching the roof.

If you see these signs, tell the roofer when you call. It narrows the visit to the place that matters, and it can change the plan from ice removal to a fix that lasts.

Photographs help. Take them from the hatch, and note the date and the weather, so the roofer can compare conditions later.

Why do some slopes and some houses build more ice than others?

Shaded north-facing slopes stay colder and hold snow longer, while complex roofs with dormers, valleys and overhangs create more cold edges. A house next door with the same snow but a simpler roof or better attic can stay clear. Roof shape and attic condition decide it, more than the weather.

Wooded hills mean more shade. Roofs in tree-covered areas, including the hills around Long Valley and Schooleys Mountain in Washington Township, Morris County, can stay frozen longer than roofs on open ground.

Dormers and valleys also catch snow and shed it unevenly. A roofer reading your roof will look at where ice forms each year and match it to the attic below. The same spot, year after year, points at a specific leak of heat.