Ice Dams on Tahoe Roofs: Repair, Removal and Prevention

What is an ice dam, and why do Tahoe roofs get them?

An ice dam is a ridge of ice that forms along the eave of a roof and traps meltwater behind it. It starts with heat. Warmth leaking from the house into the attic warms the roof deck, the bottom of the snowpack melts, and the water runs downhill under the snow. When it reaches the eave, which hangs past the heated walls and stays cold, it freezes. Every melt cycle adds another layer until a solid dam has formed. The water pooling behind it has nowhere to go except sideways and up, under the shingles, through nail holes and seams, and into the house.

South Lake Tahoe is close to ideal for building ice dams. We get 200 or more inches of snow in a normal winter, so the roof carries an insulating blanket for months. Daytime sun and nightly hard freezes cycle the melt over and over. Many homes are older cabins with thin insulation and no air sealing, and steep north-facing slopes and shaded roofs under big pines never warm enough to clear themselves. Add deep eaves and cathedral ceilings with no attic to vent, and a dam is almost guaranteed on the shaded side of the house.

What are the signs of ice dam damage?

The obvious sign is a thick band of ice at the eave with big icicles hanging from it, especially when neighboring roofs with better insulation are clear. Inside, look for water stains on ceilings near exterior walls, peeling paint at the top of walls, wet or sagging insulation in the attic, and a musty smell after a thaw. Outside in spring, look for lifted or cracked shingles along the eaves, rotten fascia boards, gutters pulled away from the house, and stained or soft eave decking. Damage that shows up only in the coldest weeks and disappears in summer is almost always ice dam related.

How do you remove an ice dam without wrecking the roof?

Start from the ground with a roof rake and pull the snow off the lower three to six feet of the roof after each storm. Less snow above the eave means less meltwater feeding the dam, and on many homes this alone keeps the problem manageable. For a dam that is already causing a leak, we use low-pressure steam to cut channels through the ice so the water behind it can drain, then clear the snow above it.

What not to do matters as much. Do not go onto a snow-covered roof; it is the most common way homeowners get hurt in winter. Do not chip at the ice with an axe, hatchet, hammer or shovel; every strike cracks shingles, and on a metal roof it dents panels and breaks seams. Do not spread rock salt or de-icer on the roof; it corrodes metal, stains shingles, kills plants below and rarely melts enough to matter. Pressure washing and blowtorches cause more damage than the dam. If you cannot do it safely from the ground, call us.

How do you repair the damage after an ice dam?

The repair depends on how long water has been getting in. A first-time leak usually means drying the interior, replacing the ice-and-water shield and underlayment along the affected eave, and re-laying the shingles or panels with new drip edge. Roofs that have dammed for years often have rotten eave decking and fascia under the shingles; we cut that out, replace the sheathing, and rebuild the eave with membrane running well up the slope before the roofing goes back on. Flashing at sidewalls and chimneys that ice has pushed apart is replaced, not caulked. Every repair we do at an eave includes the membrane the roof should have had in the first place, so the same dam cannot push water in again. Our roof repair page describes the inspection and estimate process.

What actually prevents ice dams?

Prevention is about keeping the roof deck cold, and there is an order to it:

1. Air sealing and insulation. Most of the heat that melts the snow gets into the attic through gaps: recessed lights, plumbing and wiring penetrations, the attic hatch, top plates of walls. Sealing those and bringing insulation up to a proper depth is the single most effective fix, and it lowers your heating bill.
2. Ventilation. Continuous intake at the soffits and exhaust at the ridge keeps air moving under the deck so any heat that does get in is carried away. Baffles keep the insulation from blocking the intake. Cathedral ceilings need a vented channel above the insulation or a different roof design.
3. Ice-and-water shield. Self-adhering membrane from the eave edge to at least 24 inches inside the warm wall, plus valleys and every penetration. It does not stop dams from forming, but it stops the water from getting into the house when they do. We install it on every roof we touch.
4. Metal roofing. Standing seam panels shed snow before it can melt and refreeze, and ice does not damage them. Combined with the steps above, it is the closest thing to a permanent solution for a problem roof.
5. Heat cable, as a last resort. On a section where the geometry guarantees ice, cable keeps a melt channel open. It treats the symptom, uses power all winter, and must be installed correctly to avoid damaging shingles. We recommend it only after the other steps.

Will insurance cover ice dam damage?

Frequently, but it depends on your policy and on the cause. Sudden, accidental damage, such as a leak that ruins a ceiling and insulation during one storm, is commonly covered. Damage from long-term neglect, for example a roof that has visibly leaked for several winters, usually is not. We are roofers, not insurance advisers or lawyers, so read your policy and talk to your agent. What we can do is make the claim easier: photograph the dam, the leak and the damaged materials, note the dates, provide a written repair estimate, and secure the roof so the damage does not get worse while the claim is reviewed.