If you get ice dams on the same section of roof every single winter, the weather isn't the problem. Vermont gets cold everywhere, but not every house grows a ridge of ice along the eave by February. The houses that do have something in common, and it has almost nothing to do with how much snow fell.
Ice dams in Vermont are a heat problem wearing a weather costume. Warm air escapes into the attic, melts the snow sitting on the roof above it, and that meltwater runs down until it hits the eave, where there's no warm attic underneath. It refreezes there. Do that for a few weeks and you get a wall of ice with nowhere for the next round of water to go, so it backs up under the shingles instead. That's when it stops being an outdoor problem and starts showing up on your ceiling. Here's what's actually happening up there, and what fixes it.
What an Ice Dam Actually Is
An ice dam is a ridge of ice that builds along the lower edge of a roof and blocks meltwater from draining off. Picture the roof in two zones. The upper section sits over a heated attic and runs a few degrees warmer than the air outside. The lower section past the exterior wall has nothing warm under it.
Snow on the warm zone melts, the water runs down, and when it crosses onto the cold zone it freezes again. Each cycle adds a little more ice. Give it a month of freeze and thaw and you've got a dam several inches thick, holding a pool of standing water behind it on a surface never designed to hold standing water.
Why Attic Heat Is the Real Cause
Every house leaks some heat into the attic. The question is how much. Recessed lights, bath fans venting into the attic instead of outside, gaps around the chimney chase, a hatch with no weatherstripping, thin or compressed insulation, all of it pushes warm air up. Then ventilation decides what happens next. A balanced attic pulls cold air in at the soffit and pushes it out at the ridge, keeping the roof deck close to outdoor temperature. When intake is blocked by insulation stuffed into the eaves, or when there's exhaust with no intake to feed it, that warm air sits against the deck and melts snow from below. The roof surface never gets a chance to stay cold, which is the whole point.
Ice dams in Vermont are a heat problem wearing a weather costume. A new roof over an unsealed attic will grow the same dam next winter.
The Damage You Don't See Right Away
Water backing up behind a dam gets under the shingles and soaks the deck. By the time a stain appears on a bedroom ceiling, the sheathing above it has usually been wet for weeks. Insulation gets saturated and stops insulating, which makes the next ice dam worse than the last one. Mold starts in the cavity where nobody looks. The gutters take a beating too, since a trough full of ice weighs enough to pull hangers out of the fascia and take the fascia board with them. Then there's the falling ice, which is a real hazard over a doorway or a walkway. Most of this is invisible from the driveway until the repair bill is already large.
Ice dam on your roof every winter?
Something under the roof is causing it. The inspection and estimate are free.
What Actually Fixes It
Air sealing and insulation come first, because they address the heat. Sealing the leaks between living space and attic, then bringing insulation up to depth, drops the attic temperature closer to outside. Next comes ventilation, with intake at the soffit and exhaust at the ridge, sized to work together instead of fighting each other. On the roof itself, ice and water barrier run wide at the eave gives you a waterproof layer under the shingles where the dam forms. Standing seam metal helps too, since snow slides off it before it has time to melt and refreeze. Raking snow off the lower roof is a stopgap, not a fix, and heat cable just melts a channel through a problem you still have. If the same section ices up every winter, our roof replacement service starts by reading the attic before quoting the roof.
