Roof Rakes, Heat Cables, and the Cheap Tools That Actually Prevent Ice Dams (and the Ones That Do Not)

Every hardware store in Greater Boston puts out the same ice dam display in November. Some of it works, some of it makes things worse, and one thing on the shelf will void your roof warranty. Here is what we tell our own clients to buy.

Buy: a roof rake

A long-handled rake that pulls snow off the bottom three or four feet of the roof from the ground. If there is no snow on the eave, there is nothing to melt and refreeze into a dam. Use it after every storm that leaves more than four inches. Get one with wheels or bumpers on the blade so it rides above the shingles instead of scraping them. Cost: $40 to $80. This is the single most effective thing a homeowner can do.

Maybe: heat cables

Self-regulating heat cable zigzagged along the eave and down the gutters and downspouts keeps a channel melted so water has a path off the roof. It works, and it is a reasonable fix for one chronic spot, a north-facing valley or a section over an unheated porch. It is not a solution for a whole roof, it uses real electricity all winter, and it has to be installed on a GFCI circuit by someone who knows how. Cheap cable installed badly is a fire risk. If you go this route, our electrician can install it properly.

Do not: salt pucks and sock tubes

Calcium chloride tossed on the roof or packed in a nylon stocking across the dam. It melts a channel for a few hours, then the dam refreezes around it. Meanwhile the salt corrodes the gutters, kills the plants below the downspout, and stains the shingles. Rock salt is worse: most shingle manufacturers list it as a warranty exclusion.

Never: a hammer, a shovel, or a pressure washer

Chipping ice off a roof takes shingles with it. We have replaced plenty of roof sections in West Roxbury and Milton that were fine until someone went after the ice with a hatchet. If a dam is already causing water inside, the safe removal is low-pressure steam, which melts the ice without touching the shingles. That is what we do.

The real fix is upstairs

Ice dams form because the roof is warm. Heat leaks into the attic, melts the snow from underneath, and the meltwater refreezes at the cold eave. Air sealing and insulating the attic floor, plus making sure the soffit and ridge vents are clear, is the fix that makes the rake and the cables unnecessary. It is a one-time job and it also lowers the heating bill.