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What causes icicles on your roof?

Icicles which form on the edge of your roof in the winter time are caused when the snow which is sitting on your roof melts. The resulting water runs down to the edge of your roof where it refreezes, forming icicles. Although the ice forms at the edge of the roof, the snow can melt anywhere along the roof, from the bottom edge to the peak.

Multiple factors can cause the snow on your roof to melt: inadequate insulation, house air leakage into the attic through thermal bypasses, and improper ventilation being the major causes we find. However, icicle formation is also influenced by the structure of your house, weather conditions, and even by the color of your roof. Finally, your lifestyle can affect icicle formation.

Some of the biggest factors which cause roof ice can be corrected or reduced substantially by the insulation, air sealing and ventilation work we will be doing in your home. However, not all of the factors that may contribute to ice formation on your roof are correctable and ice cannot be completely eliminated.

What is the best solution to reduce ice on my roof?

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In most cases, a combination of proper air-sealing, high levels of insulation, and adequate ventilation are the best solutions to reducing problems with roof ice.

Does raking off the snow help?

Yes. If you don’t have snow on your roof, it can’t melt and form ice. This should generally be considered a short-term fix and shouldn’t replace addressing heat loss. In some heavy snow conditions, the snow acts as an effective insulator on top of your roof, and can warm the roof deck and increase snow melting.

Shoveling the snow off the first two or three feet of the roof won’t prevent the problem. Snow further up the roof can melt down and create dams.

If you do rake the snow off—do not climb on the roof and be careful on the ground—the weight of snow falling off the roof can be dangerous.

Does heat tape help?

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Heat tape can help. However it not only costs as much as $600 to buy, it must then be installed, adding penetrations to your roof. And it can be very expensive to run. You’re essentially paying to heat your roof. This should not be considered as an alternative to reducing heat loss into the attic, and only makes sense in more rare cases with certain poorly thought out architectural details such as roof valleys over an entryway.

Should I remove big icicles and ice dams from my roof?

Do not climb up on your roof and hack or chip away at ice. This is very dangerous. And there’s substantial risk of roof damage.

Generally, you do not want to hack away at ice unless there is the risk of injury from falling ice. Trying to remove ice often damages your roof and other parts of your home.

Is there anything I can do about an ice dam on the roof right now?

In the short-term, you can buy a special “melt sock” or fill a nylon stocking with calcium chloride. Place this over the ice dam, running it up the roof right where ice is forming. This can create a channel allowing melt water to run off rather than back up into your house.

Does raking off the snow help?

Yes. If you don’t have snow on your roof, it can’t melt and form ice. This should generally be considered a short-term fix and shouldn’t replace addressing heat loss. In some heavy snow conditions, the snow acts as an effective insulator on top of your roof, and can warm the roof deck and increase snow melting.

Shoveling the snow off the first two or three feet of the roof won’t prevent the problem. Snow further up the roof can melt down and create dams.

If you do rake the snow off—do not climb on the roof and be careful on the ground—the weight of snow falling off the roof can be dangerous.

Does heat tape help?

Heat tape can help. However it not only costs as much as $600 to buy, it must then be installed, adding penetrations to your roof. And it can be very expensive to run. You’re essentially paying to heat your roof. This should not be considered as an alternative to reducing heat loss into the attic, and only makes sense in more rare cases with certain poorly thought out architectural details such as roof valleys over an entryway.

My attic is insulated. Why do I still have ice?

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In most homes we see, proper attention has not been paid to air-sealing. This allows warm air to escape into the attic and decreases the effectiveness of insulation that is there. We often see homes that how a lot of attic insulation but no air-sealing.

Even if your attic is well sealed and insulated, there are additional factors that can contribute to warming your roof and melting snow.

  • Attic Ventilation. If it is appropriate and feasible, improving attic ventilation will help control ice formation and reduce the risk of moisture damage from condensation in the winter. Attic ventilation without proper air-sealing and insulation, however, rarely fixes the problem, and increasing ventilation in these cases may cause your heating bills to skyrocket.
  • Chimneys and Flues. A chimney traveling through an attic crawlspace will radiate heat into the attic. Even if the attic is properly ventilated, some of this heat will reach the roof and melt snow.
  • Kitchen and Bath Fans. A kitchen or bath fan which is vented through the roof will generate heat and melt the snow around the fan. Icicles will often form on the edge of the roof below the roof vents of these fans. Fans exhausting into the attic can warm the entire attic creating a problem (and leading to moisture and mold issues). Fans should be vented directly outside.
  • Roof Color. Darker roofs absorb more heat from the sun, and in certain conditions can accelerate snow melting.
  • Heavy Snow Fall. Snow acts as an insulator. Deep snow on your roof can warm up the roof deck and melt snow in contact with the roof—which then refreezes at the eaves. In very heavy snow fall, even well-insulated homes may experience ice as a result. The more insulation you have, the less likely this is to occur. With deep snow cover, roof raking may be helpful.
  • Outdoor Temperature. The outdoor temperature impacts ice formation. Each home responds differently to different temperatures, but temperatures in the low 20s seem to generate the most ice for most homes. At this temperature, it is warm enough so the roof can melt some snow, but cold enough so that it refreezes quickly at the eaves.
  • Indoor Temperature. The higher you set your thermostat, the more heat loss you will have, regardless of insulation levels.
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