Ask an Old House Pro

Banishing Ice Dams

Partner Post: Maine Preservation

In a monthly column, the experts at Maine Preservation answer your questions about maintaining antique and vintage homes.

Q: “I’ve been having problems with ice dams on the roof of my 100-year-old house this winter. Is installing electrical heat tape a good idea?”

– Margaret Keyser, South Portland

A: It’s easy to understand why heat tape, a.k.a. heated cables, seems like a good idea. Attached with clips along the roof’s edge in a zigzag pattern, the cables help prevent a buildup of solid ice in gutters and along eaves — a.k.a. ice dams — that can lift shingles and cause leaks. The system is affordable and fairly easy to install, but don’t be fooled: this is a short-term, marginally effective solution and is not recommended as a permanent fix.

First of all, heated cables need to be monitored for safety. They are often plastic coated, so it’s essential to ensure the material remains pliable and sealed to function correctly; older cable systems can become hard, brittle, and riddled with cracks. Throw in the damage rodents can wreak and you have a potential fire hazard. If you want to go the heat tape route, we recommend one of the newer systems, which enclose the cables in protective metal standing-seam roof panels, known as ice belts, installed just above the gutters. The metal itself also helps prevent ice dams by allowing the snow melt from above to run off at a faster rate than it would on asphalt shingles.

Secondly, heated cables consume electricity — perhaps more than you would expect. If you must use them as a stopgap remedy, make certain they are either hardwired or plugged into a GFCI outlet, which automatically shuts off if water improperly comes into contact with an electrical product, preventing deadly shocks. GFCIs are required by national code in all kitchens, bathrooms, garages, and outdoor areas. Finally, make sure to disable the heating system in the warmer months so you’re not wasting energy.

The existence of ice dams on or near roof eaves is symptomatic of an improperly vented attic and roof. That’s your fundamental challenge. When interior heat is trapped and warms the underside of the roof, snow melts and drains away toward the eaves where it freezes, forming a dam. Instead, you want the entire roof to remain the same temperature as the eaves — i.e., ice cold. An experienced roofer or contractor can assess whether you have the necessary soffit and ridge ventilation and attic floor insulation to maintain a chilly surface of shingles.

To deal with existing dams, you can hire a snow removal expert to remove the blockages manually or with a heated pressure washer. We do not advocate raking asphalt roofs as it shortens the life of the shingles by removing the aggregate particles. Another option is to purchase one of the melting products (most use calcium chloride) available at hardware stores and online. Keep in mind that while these products are effective, the chemicals they contain can damage foundation plantings, so use caution when applying.

One last thought: If you’re still considering heat tape, please be safe! Do not ever crawl onto an icy roof to install or inspect the cables. Put them in place on a warm day when the roof is clear and dry — preferably well before temperatures are forecast to drop.

Have an old house question for the Maine Preservation pros? Leave a note in the comments and you may be featured in an upcoming column!

Christopher W. Closs is field service advisor for Maine Preservation, the only nonprofit historic preservation group working to preserve and protect treasured places across the state of Maine. Closs holds a Master’s Degree in Historic Preservation from the University of Vermont and is skilled in restoration carpentry and stone masonry. You can email additional questions to [email protected] and find more helpful information at

One Comment

  1. J.B.

    My lovely old Cape/Bungalow has rock cellar walls that need repointing. I want to do the job myself and don’t know what compound to use, the best approach, cautions, and what tools will make it easier.

    I’ve found conflicting information about what mortar to use, what mortar not to use, recommendations about above and below the frost line. A commercial product called “historic pointing mortar” sounded promising, but the minimum purchase of a pallet wasn’t feasible.

    There are various mortar recipes online, but they make a very large amount at a time and the ingredient descriptions, amounts, and directions are so ambiguous I don’t feel confident using any of them.

    I would like to mix up a pailful of mortar and work for an hour or two at a time. Could you provide a recipe that creates a small portion of appropriate mortar, and also some tips, e.g., where to start first, the need to insert backing before the mortar, how far the mortar should be pushed in between the rocks, the frost line and places where water seeps in?

    Really enjoy your column! Thank you.

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