Ice dams can form on a metal roof, but a well-built standing seam roof usually copes with them better than shingles because it has no horizontal joints for backed-up water to enter. The ice still comes from the same source, heat leaking out of the house, so the lasting fix pairs a cold, well-insulated attic with roof details that keep meltwater out.
New Jersey’s energy code places Middlesex, Mercer, Monmouth, Union and Essex counties in climate zone 4A and Somerset, Morris and Hunterdon in the colder zone 5A, according to DCA Bulletin 22-1. This guide explains how ice dams form, how different metal roofs handle them, what the code requires and what actually prevents them.
Architectural Metal Panels fabricates standing seam roof panels and trim in New Jersey for roofers and owners. We do not install, so the installation points below are guidance to share with your roofer.
Why do ice dams form on a metal roof?
Ice dams form when heat escaping from the house warms the upper roof and melts the snow on it. The water runs down to the colder roof edge, freezes and builds a ridge of ice that traps more water behind it, as the University of Minnesota Extension explains. The roofing material does not change that physics.
What metal changes is how long snow stays put. A smooth metal surface often sheds snow sooner than shingles, which can leave less snow to melt and refreeze. Snow still hangs on at low pitches, behind snow guards, in valleys, above dormers and on north-facing slopes. Overhangs stay cold because no heated room sits below them, and that is where the ice builds.
The heat sources are the same as on any house: gaps around attic hatches, recessed lights, plumbing and wiring chases, bath fans vented into the attic, and thin insulation over cathedral ceilings.
Do metal roofs leak because of ice dams?
They can, depending on the panel type and the details. A standing seam roof resists backed-up water better than a lapped roof, but no roof stays watertight with water pooled above its seams for days.
| Roof type | How it handles backed-up water | Weak points |
|---|---|---|
| Mechanically seamed standing seam | Seams are folded tight and stand above the pan; panels often run eave to ridge without end laps | Eave and valley flashings, penetrations, sidewalls |
| Snap-lock standing seam | Seams stand above the pan but rely on a snapped joint | Seams can open under heavy snow and ice movement |
| Exposed-fastener panels | Water must get past end laps and many screw holes | End laps, screws, low slopes |
| Metal shingles and shakes | Interlocking pieces shed water but have many joints | Joints near the eave, valleys, underlayment |
Sheffield Metals warns that snap-lock seams are more prone to disengaging from the thermal movement of built-up snow and ice, and it suggests mechanically seamed panels in snowy regions. That is worth weighing on low-pitched roofs and shaded slopes. Our standing seam roof panels page compares the two seam types in more detail. Once your roofer settles on the seam, put it on the cut list you send us.
Does New Jersey code require ice and water shield under a metal roof?
Only in Sussex County. The state requires an ice barrier where the average daily January temperature is 25 degrees F or lower, and state guidance identifies that area as Sussex County, according to DCA Bulletin 07-3. Everywhere else in New Jersey, it is not a code requirement.
It is still standard good practice, so ask your roofer to plan on it at the eaves. Under metal, the membrane should be a high-temperature product, because a metal roof gets hot enough in summer to soften some ordinary membranes. Valleys, low-slope sections and the areas around chimneys and skylights benefit from the same protection.
What actually prevents ice dams?
Keep the whole roof deck cold and evenly cold, then back it up with roof details that tolerate some ice. The University of Minnesota Extension stresses cutting heat loss into the attic first, through air sealing and insulation, along with ventilation.
- Seal air leaks from the living space into the attic: hatches, top plates, chases, recessed lights and duct runs.
- Add insulation on the attic floor once the leaks are sealed.
- Vent the roof deck from soffit to ridge so outside air keeps the underside of the roof cold. Cathedral ceilings may need a vented air space above the insulation.
- Send exhaust fans outdoors. Bath and kitchen fans should never vent into the attic.
- Ask your roofer for a high-temperature ice barrier at the eaves and in valleys.
- Choose the right seam for the pitch and exposure, and keep penetrations out of valleys and eave zones.
- Give meltwater a path. Eave trim, valleys and any built-in box gutters must drain freely.
Roofing alone cannot fix a warm attic. If ice dams formed on the old roof, plan the attic work alongside the new metal roof rather than after it.
Should a metal roof have snow guards, and do they make ice dams worse?
Snow guards stop snow from sliding off in one heavy sheet onto walkways, decks, cars, lower roofs and gutters. Because they hold snow on the roof longer, they work best on a house with a cold, well-vented attic.
Layout depends on the roof’s pitch and length and on the snow load at the address. New Jersey has designers pull ground snow values for the exact location from ASCE 7 hazard tools. Where a tool flags a site as a case study, DCA Bulletin 19-1 allows fallback ground snow loads of 35 psf in Hunterdon and Morris counties and 30 psf in Somerset County.
On standing seam, guards can clamp to the seams. S-5!, a maker of seam clamps, says its clamps attach equipment without penetrating the roof. Our guide to snow guards for metal roofs covers layout in more depth.
Are heat cables a good idea on a metal roof?
They can tame one stubborn trouble spot, but they treat the symptom rather than the warm attic. If you use them, choose cable and clips made for metal roofs that attach without drilling through the panels. Run the cable through the gutter and downspout so meltwater does not refreeze lower down. Have an electrician wire the circuit, and expect the running cost to show up on winter electric bills.
How should you remove an ice dam from a metal roof?
Carefully, from the ground, and never with a hammer, a chisel or rock salt.
- Use a roof rake with a plastic or rubber-edged blade to pull fresh snow off the lower roof from the ground.
- Do not chip ice. A blow hard enough to crack ice can dent a panel, scratch the finish or open a seam.
- Skip rock salt and calcium chloride, which can damage metal finishes and the plants below.
- Stand clear of the eaves. Snow on metal can let go all at once.
- If water is coming inside, protect floors and furniture and call for help before climbing anything.
What should you ask before buying a metal roof for snow country?
Ask your roofer how ice at the eaves will be handled, not just which color you want.
- Snap-lock or mechanical seam for my pitch and exposure?
- Which high-temperature ice barrier goes at the eaves and valleys?
- How will the attic be vented, and who will look at air sealing and insulation?
- Where will snow guards go, how many, and how are they attached?
- How are valleys, dormers, chimneys and box gutters detailed?
- Was the snow load checked for my address?
- Who sends the panel lengths and trim list to the fabricator, and who checks the order when it arrives?
The answers belong in your roofer’s written contract. Our metal roof panel prices page explains what drives the cost of panels and trim, and the metal roofing panels hub covers the panel types we make.
Ice dams and metal roofs: common questions
Do metal roofs get ice dams?
Yes. Ice dams come from heat escaping into the attic and melting snow that refreezes at the cold eave, and that happens under any roofing. Metal often sheds snow sooner, and a standing seam roof resists backed-up water better than shingles, but the attic still has to stay cold.
Is ice and water shield required in New Jersey?
Only in Sussex County, where the code’s ice-barrier rule applies because the average January temperature is 25 degrees F or lower. Elsewhere in the state it is not required, but it is standard good practice at eaves and valleys, so ask your roofer to include it.
Will snow guards make ice dams worse?
They keep snow on the roof longer, which gives a warm attic more time to melt it. On a house with good air sealing, insulation and ventilation, that matters little. Guards are often the safer choice anyway, because snow sliding off metal can damage gutters, decks and cars.
Can I use rock salt or ice melt on a metal roof?
Avoid it. Chloride salts can damage metal finishes, stain the roof and harm the plants below. Use a roof rake from the ground to clear snow from the lower roof, and leave ice removal to someone who will not damage the panels.
Is standing seam or exposed-fastener metal better for ice dams?
Standing seam. Its seams sit above the flat of the panel, and panels often run in one piece from eave to ridge. Exposed-fastener panels have end laps and many screw holes that backed-up water can reach, which makes them a poor fit over living space where ice dams are likely.
Does a metal roof need attic ventilation?
In most homes with an attic, yes. Venting from soffit to ridge keeps the roof deck cold in winter, which reduces ice dams, and helps the attic dry out. Cathedral ceilings and unvented assemblies need a design that handles both heat loss and moisture.
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Standing seam panels for New Jersey winters
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