The winter mechanics

Ice dams and metal roofs, explained honestly

An ice dam is house heat leaving through the roof and refreezing at the eave. A standing seam metal roof takes away the dam's raw material and its leak path, and it leaves the heat leak untouched. Both halves of that sentence matter, and roofing sales pitches tend to mention only the first. Here is the full mechanism.

How the dam gets built

Snow lands on the roof and stays: New Hampshire design values run from about 50 pounds per square foot in the southern tier to more than 120 in the mountains, per CRREL TR-02-6, and an asphalt roof carries much of the season's blanket for months. Heat escaping the living space warms the deck above it, melting the blanket from below even on below-freezing days. The meltwater runs down the roof plane until it crosses the eave overhang, the one part of the roof with no warm house under it, and refreezes there. Each cycle adds a layer, the ridge grows into a dam, and water ponds behind it, held against the roof surface uphill of the ice.

On shingles, ponded water is the endgame. Asphalt sheds falling water, not standing water: it wicks under laps, finds nail penetrations, and shows up as the classic February stain at the top of an exterior wall. The other winter tell, icicles the size of fence posts, is the same mechanism advertising itself.

What standing seam changes

The blanket mostly leaves. A smooth panel surface sheds snow instead of storing the winter, so the melt engine has far less fuel sitting over the heated house.
The leak path closes. Panels run eave to ridge with no horizontal laps and no exposed fasteners, so even where eave ice forms, ponded water has nothing to wick under. This is the structural difference, and it is why the ice dam war stories are an asphalt genre.
The failure mode moves to the ground. Shed snow arrives below all at once, which is why retention over doorways, decks, and equipment is part of the design, engineered on the snow guards page.

What standing seam does not change

The heat leak is a building problem, not a roofing problem. An attic that leaks warm air keeps leaking it under any roof material, and that costs money every month whether or not it ever stains a ceiling again. Air sealing the attic floor, insulation to a sane depth, and real ventilation (soffit intake, ridge exhaust, baffles keeping the path open) attack the cause. The reroof is the cheapest moment those details will ever have; a good installer rebuilds ridge and soffit venting as part of the project, which is one more line to look for in the written quote. What belongs in that quote, and how to check the person offering it in a state with no roofing license, is the hiring guide's territory.

The honest decision path

If ice dams are the reason you are reading about metal roofs, run the sequence in order: fix the attic if it is bad, price the conversion honestly (about 2x asphalt, ranges in the cost guide), and treat the roof swap as buying out the leak path and the February drama at the same time. The system details live at standing seam metal roofing, the project at metal roof replacement, and the statewide decision framework at the New Hampshire Metal Roofing Guide. Ice dam calls cluster where thaw cycles do: Manchester and Nashua and the Monadnock hills see the worst of the freeze-thaw seesaw.

Ice dam questions

Will a metal roof get rid of my ice dams?

It removes what ice dams need to do damage: the standing snow blanket mostly sheds, and there are no shingle laps for backed-up water to work under. It does not fix the attic heat loss that melts snow in the first place, so on a leaky attic some eave ice can still form; it just stops being a leak path.

What actually causes an ice dam?

Escaping house heat. The attic warms the roof deck, the underside of the snow blanket melts, meltwater runs down to the cold overhanging eave, and it refreezes into a growing ridge that ponds water behind it. On asphalt, that ponded water backs up under shingle laps and into the wall and ceiling below.

Are heat cables worth installing?

As a bandage, sometimes; as a plan, no. Heat cables spend electricity melting drain channels through a symptom while the heat leak that causes it keeps running. They earn their keep on stubborn problem eaves and valleys where insulation fixes are impractical, and they should embarrass any new-roof design that needs them from day one.

Should I fix insulation before or with the new roof?

With it, ideally. Air sealing and attic insulation are cheaper than roofing and cut the melt engine on any roof material; a reroof is also the one moment ventilation details (ridge vent, soffit intake, baffles) can be rebuilt at marginal cost. Do the roof alone and you have solved the leak path but still pay the heat bill.