Roof Ice Damming

An ice dam is an accumulation of ice at the lower edge of a sloped roof, starting three or four feet up on the roof edge and ending at or in the gutter. When interior heat melts the snow on the roof, the water will run down and refreeze at the roof’s edge, where temperatures are much cooler.

Eventually, the ice builds up and blocks water from draining off the roof. This, in turn, forces the water under the roof covering and into your attic or down the inside walls of your house. Once an ice dam forms, the potential damage can be serious. Take these steps now to avoid trouble later:

1. Keep the attic well ventilated. The colder the attic, the less melting and refreezing on the roof.

2. Keep the attic floor well insulated to minimize the amount of heat rising through the attic from within the house.

This two-step approach decreases the likelihood that ice dams will form, or at least, reduces their size. As an extra precaution against roof leaks, in case ice dams do form, install a water-repellent membrane under your roof covering.

Unfortunately, ice dams may be unavoidable if your home has recessed lighting near the roof. Heat generated from these lights melts snow, which then contributes to ice dam buildup. The only sure way to avoid this problem is to eliminate recessed light fixtures near the roof.

If you already have an ice dam, do not get up on the roof and try to break it up with a hammer, ice chopper, or ax. You will damage your roofing by taking the grit off the shingles or even breaking them. If you have an ice dam, the only thing you can do is to take some old nylons and cut the legs off. Then, fill the legs with salt or a chemical ice-melter and tie the ends closed. Put them on the roof so they run up the roof, over the ice dam and to the lower edge of the roof. This will melt through the ice dam and make a path for the melting snow to run off the roof. Put several of these on the roof to make several channels for the water to run off. The salt or chemical will not hurt the roof. You have more of a chance of damage from the ice if it is left in place.

When preparing to work on the roof, make sure you clear the ground of snow and ice and have your ladder stable. You might consider putting deicing cables on the roof this spring or summer. It is too late to put them on now if you have ice dams. This cable creates just enough heat to keep an open channel for the water to run off. The proper way to place the deicing cable is to zig-zag it up and down on the over-hang so it goes just over the lower edge of the roof. Then you lay the deicing cable in the bottom of the gutter and down the downspout. That way, the melting snow has a path to follow out and down to the ground. This is also good in valleys that build up with ice.