Best Ice Dam Prevention Products, Ranked

It isn't a product you buy off a shelf, and that's why it gets skipped. The University of Minnesota Extension's first long-term step is to make the ceiling airtight so no warm, moist air flows from the house into the attic. The DOE's Building America Solution Center calls air sealing the most important step, and ENERGY STAR recommends air sealing the attic before adding insulation.

The leaks are the gaps you can't see from the attic hatch: around light fixtures, bath fans, chimneys, plumbing and wiring runs, and the hatch itself. Building Science Corporation's Joseph Lstiburek sums up the fix as "air tightness, air tightness, air tightness", and for existing attics suggests spray foam at the leaks before more insulation goes on.

Once the air leaks are sealed, insulation slows the heat that still conducts up through the ceiling. ENERGY STAR's retrofit guidance for climate zone 5, which covers Kent, Ottawa, Allegan, Ionia and Barry counties, is R-60 for an uninsulated attic and R-49 where there are already 3 to 4 inches.

ENERGY STAR lists ice dams as one of the signs a house needs more attic insulation. Building Science Corporation's ice dam digest gives R-30 as a bare minimum below a ventilated attic, so treat that as a floor, not a target.

Ventilation flushes the heat that gets past the air sealing and insulation, so the deck stays close to the outdoor temperature. GAF's technical bulletin on ice dams names proper ventilation as a key preventive measure because it lowers attic temperature and reduces snowmelt. The DOE says vented attics should keep at least a 2-inch air gap between the insulation and the roof deck, with baffles running from soffit to ridge.

Skip the powered attic fan. The University of Minnesota Extension says mechanical attic ventilation is not a recommended solution to ice dams, because it can create other attic moisture problems and pull the house into negative pressure. We correct the ventilation on every roof we replace.

Pulling snow off the lower roof takes away one ingredient an ice dam needs, and the University of Minnesota Extension lists it as a short-term measure. Travelers Insurance suggests clearing 3 to 4 feet up from the roof edge. Slide-style rakes such as the Avalanche! Original 500, which retailers list with a 16-foot handle and a plastic slide for asphalt shingles, are aimed at the first several feet of roof.

Two cautions. UMN warns that a roof rake can damage roofing materials, so use a light touch and never chip at ice. And CertainTeed's VYCOR data sheet notes that clearing the roof edge may not prevent an ice dam, only shift where it forms. If you can't reach the eave from the ground, don't climb. Our roof snow and ice removal service does it without damaging the shingles.

Self-regulating cable adjusts its own output to conditions. Raychem IceStop, now published by Chemelex, puts out about 12 watts per foot in snow or ice at 32°F and about 5 watts per foot in dry air, and Chemelex says the self-regulation keeps it from overheating even where the cable crosses itself. It's rated for shingle, metal and several other roof types, and for metal or plastic gutters and downspouts.

Know what it does. Chemelex says a heated path from the roof to a safe drain point keeps ice dams from forming along that path; it is built to carry away meltwater, not to melt accumulated snow, and it won't stop snow sliding off the roof. CertainTeed's VYCOR data sheet adds that heat cable may shift an ice dam rather than prevent it. HotEdge Rail is a variation that mounts a self-regulating cable in a metal rail on the fascia, under the drip edge, so nothing penetrates the roof.

The plug-in kits sold at hardware stores, such as Frost King's RC series and Warmup's WRGH kits, are constant wattage: the same output along the whole length regardless of conditions. Frost King's run 5 watts per foot at 120 volts in fixed lengths that can't be cut or altered. Without a temperature controller, WarmZone says constant-wattage cable will burn itself out, and Frost King calls its Roof Sentry control highly recommended.

Read the limits before you buy. Frost King says its kit is for shingle roofs only, never metal or flat roofs, and not for combustible materials. Warmup's manual says the heated cable must never touch, cross or overlap itself, must stay clear of leaves and pine needles, and must plug into a grounded, ground-fault protected outlet. The CPSC has warned for years against using pipe heat tapes on gutters.

Travelers Insurance describes the trick: fill a nylon stocking with calcium chloride ice melt and lay it across the dam, running up and down the roof, so it melts a channel for the trapped water. Travelers is specific that rock salt, sodium chloride, should not be used because it can damage the roof. Calcium chloride also works colder: the Minnesota Pollution Control Agency puts its practical limit at -20°F, against 15°F for rock salt.

It's still a chloride. MPCA rates both calcium chloride and rock salt high for corrosion of metals, and all chloride melts harm plants, so tarp the shrubs below, as Travelers suggests. The University of Minnesota Extension offers another temporary option: hosing a channel through the dam with tap water on a warm day. Our own advice is to keep salts off the roof when you can, and call.

Snow guards show up in ice dam searches, so here's where they fit. They hold snow on the roof so it melts or drops off in small amounts instead of avalanching onto people, gutters and anything below. That's a job heat cable can't do: Chemelex says its cable won't keep snow or ice from falling and points to snow fences or snow guards to stop snow movement.

They don't stop ice dams. On a metal roof they're essential, which is why we design snow retention into every metal roof we install.