What is causing icicles?

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Posted by: from Toronto
2/27/2015 at 9:08:00 PM

Hi pros,

I have enormous icicles being built outside my house. Any ideas what maybe causing it?

Thanks for your responses.


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Brian from Next Restoration in Rockwood
Date/Time2/27/2015 at 10:12:17 PM

You could have an insulation issue in your attic causing ice damming which results in icicles forming.

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Date/Time2/27/2015 at 10:22:42 PM

Hi Olivia,

For the most part, they are created by a lack of insulation in your attic. As the snow sits on your roof, the bottom layer begins to melt from the heat escaping through the attic. As the water begins running off, it freezes when it hits the "cold zone" at the eaves. You should see a large ice cube in your gutters and your downspout is filled with ice as well. Since there is no other place to travel, it drips off the roof and freezes before it has a chance to fall to the ground.

This ice at the eaves also presents a problem called an ice dam. The water that melts from the heat in the attic gets trapped between the already frozen ice at the eaves and has no place to go except into your house. This water backs up under the shingles and enters through gaps in the roof deck or other holes that might be present. That's why we get calls about water dripping inside the house and running in front of a window. If not caught in time, the damage can be extensive.

To help eliminate this in the future, your best to call an insulation company and have them inspect the attic insulation and also call a roofing company in the summer and have your roof inspected to make sure you have an ice and water shield membrane along the eaves.

Enjoy your winter.

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James from Odd Job James in Scarborough
Date/Time2/27/2015 at 10:33:41 PM

Hello Rizzo,

This is what we call ice-damming. Your attic is poorly insulated and the heat is escaping into the attic. The attic should be the same temperature as the outside air. As heat rises to the highest point (the peak) it melts the snow which runs down towards the eavestrough where it meets cooler air and refreezes. As this process continues, the icicles get longer and bigger. The ice also makes it way under the shingles and onto the sheathing where it can mold when it melts and also drip onto the ceiling below also causing mold and water damage. The weight of the ice can also damage eavestroughing and fascia. Proper venting and insulation will add years to the life of your roof.

This problem is usually accompanied by poor air flow through the attic. Unvented soffits and possibly insufficient roof venting. You should have these things checked out and remedied to avoid further damage and expense. You'll save money on energy bills too. Depending on the age of the home, you may only have single batt R12 insulation whereas R50 is the targeted range for attics.


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Date/Time3/4/2015 at 3:19:46 PM

The primary cause is hot air escaping into the attic and then lack if insulation. Look for ice on the inside of your roof then look around that area for holes down into the house that the warm air is coming up and plug those holes. Often problem areas are where pipes and wires are coming into the attic, bathroom fans, pot lights and the access hatch to the attic. Once you have stopped the warm air getting into the attic then put in more insulation.

Make sure the insulation does not block the air vents under the soffit. You need air flow from the soffit to the roof vents otherwise your roof gets too warm in the summer and it will shorten the life of your shingles.

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