What is Ice Damming and How Do You Prevent It?

For today’s post we wanted to talk about Ice Damming, as it is an issue that affects many home owners in cold regions like Calgary, and can be severely damaging for your home’s roof if left unchecked. Ice damming is basically snow that has melted from somewhere on your roof, and then frozen again before it has descended to the ground, which then plugs up the flow of water from your roof. There is a little more technicality to it, but that is the essence of an ice dam. When you see what you think are neat icicles, you might actually be seeing an ice dam. Unfortunately these beautiful structures may have a more dangerous reality. Depending on the cause, you may need a roofing company to help you put in a fix.

What is an Ice Dam?

As briefly mentioned, an ice dam is formed when the snow under a snowpack melts from your roof top, travels to an eave, and then freezes there. These may (especially over time) block the flow of meltwater down your eaves once they freeze them over. As more snow melts and then freezes as ice, the ice dam grows, and with it the danger to the structure of your home.

Why are ice dams dangerous for the home?

The concern with ice dams is relatively straight forward. If meltwater cannot find it’s why down the usual route through the eaves, it will find the next least path of resistance. Often times this path may be back up your roof under the shingles, and into the home and through the walls. Water that runs down the wall exterior will freeze, but water on the interior of walls will lead to water damage over time.

In some cases, the dams have gained such weight that the eaves have broken off the roof structure. However, these are much easier to deal with. A leak on the other hand can be very problematic, especially if this is something that has been happening over a number of seasons now. Water within the walls of the home or attic will lead to deterioration and often the growth of mold. If this gets bad enough, you’re going to have a very expensive remediation project on your hands.

How does it form?

While ice dams form because of below freezing temperatures, the real culprit Is poor attic insulation. You want your attic insulation to be sufficient enough so that heat from the living areas don’t stay in the attic. You want your attic to essentially be the same temperature as the outside.

Ironically, dry snow is a relatively good insulator; so when you have deep snow deposited on roofs, the layers closer to the roof will be insulated by the layers on the outside. When the bottom insulated layer is met with heat from a poorly insulated attic, it will melt. This meltwater then runs down and freezes once it heats the eave.

Mitigating ice dam formation and damage

The most effective way to prevent ice damming is by ensuring that your roof and attic have been built well and insulated properly. This will depend on whether you’re living in an older home, which was likely built to different building standards; or whether you’re building a new home or otherwise having your roof replaced.

Attic Insulation

Ironically, an uninsulated attic will not create ice dams, as the constant flow of heat through attics will typically melt whatever snow lands on the roof, leading to minimal accumulation. However with the Alberta climate, this would lead to some pretty serious heat loss over the winter months, and even so on cooler summer evenings. It would also lead to sweltering heat during the summer months as an uninsulated attic will do nothing to keep the cool air within the home. So either your home would be unbearably hot on certain days, or your AC unit would see extra strain on its function. Realistically, with Alberta building codes you would not see an uninsulated attic these days anyway. Therefore the culprit is typically poor insulation, and increasing the R value of your attic should be your first step. Generally this is something you should leave to the professionals, especially if you will be using spray foam. Natural Resources Canada has a good overview of attics and insulation to get you a little bit familiarized. For attic insulation, a value of R-31 is considered good, R-50 is better, and R-60 is best.

Ventilation and Air Sealing

Aside from attic insulation, the other major way to mitigate ice dam formation is by making sure that the attic ventilation is sufficient and that you do not have have any house heat leaking into the attic. Proper air sealing will minimize warm air entering from the house, and proper ventilation will ensure that warm and humid air is removed as efficiently as possible. This will minimize the chance of condensation forming on the inside of the attic, as well as melting any snow that is in contact with the roof surface on the outside.

1 square foot of ventilation (called Net Free Area) per 300 square feet of attic space is the is the minimum requirement. Ideally this is split between the intake (soffit) vents and outtake (roof) vents. Soffit vents are done by the length of the soffit, however the r