Ice Dams on Montana Homes: What Causes Them and What to Do

What an ice dam is

An ice dam is a ridge of ice that builds up along the lower edge of a roof. Snow on the upper roof melts, the water runs down to the overhang, and there it hits a colder roof surface and freezes. Each melt adds to the ridge. Eventually water pools behind the ice and works its way under shingles or through laps, into the roof deck, walls, and ceilings.

Why it happens: heat from the house

On a cold day the roof over a heated house should stay close to the outdoor temperature. When warm air from the house leaks into the attic, or the attic floor doesn't have enough insulation, the roof deck warms up and melts the snow from underneath. The overhang sits outside the walls with no heat under it, so the meltwater refreezes there. ENERGY STAR describes it the same way: snow melts off a roof over an attic that is too warm, then re-freezes at the gutters.

That's why ice dams are as much an attic problem as a roof problem. The usual causes are:

• Air leaks into the attic around light fixtures, plumbing and wiring holes, chimneys and flues, attic hatches, and the tops of interior walls. ENERGY STAR lists ice dams as a common symptom of a home that needs attic air sealing.
• Thin or uneven attic insulation, especially low spots near the eaves and over additions.
• Blocked or unbalanced ventilation. Soffit vents buried under insulation can't bring cold air in to keep the roof deck cold.
• Heat sources in the attic, such as ductwork, bath fans that dump into the attic, or recessed lights.

Heavy icicles and odd melt patterns are early clues. See our guide to what icicles and snow melt patterns say about heat loss.

Signs you have an ice dam (or had one)

• A thick band of ice along the eaves or in gutters, often with heavy icicles.
• Water stains or peeling paint on ceilings and walls near the outside walls, especially upstairs.
• Damp or frosty spots in the attic near the eaves.
• Stained soffits or fascia, or wet window trim after a thaw.

What to do right now

• Stay off the roof. Icy roofs are dangerous, and chopping at ice with a hatchet or shovel damages the roofing.
• Pull snow off the lower roof from the ground with a roof rake if you can do it safely and you're clear of power lines. Less snow means less meltwater feeding the dam.
• Catch any water inside, move valuables, and take photos for your records.
• Call or text us at 406-210-3168 if water is coming in. We take emergency calls and messages 24/7; see our emergency roof page.

How to stop ice dams for good

Removing ice treats the symptom. The lasting fix is to keep the roof deck cold and give backed-up water nowhere to go:

1. Seal air leaks in the attic floor. ENERGY STAR recommends air sealing before adding insulation.
2. Bring attic insulation up to a sensible level, evenly, all the way out to the eaves, using rafter baffles so the soffit vents stay open.
3. Balance the ventilation: intake at the soffits and exhaust at or near the ridge, so cold outside air keeps the underside of the roof cold.
4. Waterproof the eaves. Ice and water shield at the eaves and in valleys seals around nails so backed-up water can't get in. Where ice dams are common, building code calls for it at the eaves.

How Revive helps

Revive inspects both the roof and the attic. We look for the leaks and the reason behind them: air leaks, missing insulation, blocked soffits, and poor ventilation. Then we fix the roof damage and the roof and attic insulation and ventilation problems that caused it, so you're not paying for the same repair next winter. When the roof needs replacing, ice and water shield and balanced ventilation are part of every roof we install, not upgrades.

Sources

• ENERGY STAR: About Attic Ventilation (ice damming)
• ENERGY STAR: Attic Air Sealing Project
• ENERGY STAR: Attic Insulation Project
• U.S. Department of Energy: Air Sealing Existing Attics
• Mass.gov: Roof collapse and snow removal safety

Sources are public pages we checked on November 13, 2026. This guide is general information, not engineering, insurance, or legal advice.