Icicles hanging off of roof edges are an iconic sign of winter. Unfortunately, they're also a sign of ice dam formation. Ice dams allow water to build up on your roof without properly running off, which can rapidly cause damage. Severe ice dams can also cause water to drip through your roof sheathing into your home, causing damage to your attic and ceiling.

Ice dams are also troublesome to remove — chipping away at them can rip off roofing shingles attached to the ice. Prevention is the preferable way to stop ice dams from causing water to leak into your home, and the best way to accomplish that is to upgrade your attic insulation. To learn more about what causes ice dams to appear on your roof and how attic insulation can stop them, read on.

How Do Ice Dams Form?

Ice dams form on a roof when the topmost part of the roof becomes hot enough to melt snow. All of the warm air inside your home will naturally rise through air gaps in your ceiling until it reaches the highest point of your attic. The warm air begins to warm up the roof sheathing, which in turn warms the roof shingles on top of it. Once the shingles become warm enough, they begin to melt the snow.

Once the snow starts melting, it begins traveling downwards off of your roof. However, the lower parts of your roof near the eaves are colder than your roof's ridge — they're not warmed as much by the air inside the attic. Once the water reaches the eaves, it dips below freezing temperatures again and forms an ice dam.

What Damage Can Ice Dams Cause to Your Home?

As their name implies, ice dams block the flow of water. Snow continues melting on the top of your roof and flowing downhill until it's stopped by the ice dam. Some of the water will re-freeze and rejoin the ice dam, but much of it will remain in liquid form.

Asphalt roofs aren't designed for large amounts of standing water. They're overlaid in runs, and there's a very tiny gap underneath of each shingle. Water is wicked up into the gap and back uphill towards the top of your roof. Severe ice dams can submerge shingles entirely.

Eventually, the water will find its way to your roof sheathing and damage it. Saturated roof sheathing will also leak water into your home, which can cause mold growth or water spots on your ceiling.

How Can Attic Insulation Help Prevent Ice Dams?

In order to prevent ice dams, you need to keep the entirety of your roof cold. You can't allow the ridge of your roof to warm up past the point where it starts melting snow. The best way to accomplish this is to improve your attic insulation.

When it comes to keeping a roof cold, the two forms of thermal transfer you can prevent are convection and conduction. Convection occurs when warm air is allowed to flow towards the roof and conduction occurs when the roof sheathing and the rafters begin to warm up and transfer heat to the shingles above.

Attic insulation can prevent thermal transfer from both convection and conduction. Every form of insulation acts as an air barrier — it significantly slows down the rate at which air can move through it. Insulation is also very porous, and the numerous gaps between solid particles slow down thermal transfer by conduction.

When you improve the insulation in your attic, whether by adding more insulation or changing the type of insulation you have to one that's more effective, you reduce the ability of warm air in the interior of your home to heat up your roof sheathing. When your entire roof is kept cold, snow won't melt and form ice dams.

If you've noticed ice dams forming on your roof, call an insulation contractor in your area to improve your attic insulation. All forms of attic insulation are effective at preventing ice dams, and an insulation contractor can help you find one that works best in conjunction with your attic's current form of insulation.