How Roof Ice Dams Form & How To Help Prevent Them

You’ve probably driven past homes with large icicles cascading over the edge of the roof. As beautiful as these ice formations may be, they are not a good thing. Known as ice dams, they can wreak havoc on your roof structure. The ice can work its way under shingles, prying them off the roof deck. Before long, you’ll have a leaky roof and a rotten roof deck.

Clearly, ice dams are a nuisance best avoided. So, if you live in a snowy area, ice dam prevention should be high on your list of priorities.

How Ice Dams Form

Once you understand how ice dams form, it’s easier to know how to prevent them. Picture a snow-covered roof. Now, imagine if some of the snow near the peak of the roof were to melt. The water from the melting snow would slowly trickle down towards the roof’s edge. Typically, the edges of the roof are cooler than the peak. So, when the melted snow reaches the roof’s edge, it re-freezes into ice.

This cycle of melting and refreezing can continue throughout winter. As the weeks pass, the ice formations grow larger and larger. All it takes is a little ice to work its way under a shingle. Then, as the ice dam melts, water seeps under the shingles. The water comes into contact with your roof deck — the structure your shingles are attached to. And since the roof deck is made from wood, this moisture can cause it to rot.

Once your roof deck has prolonged water exposure, roof damage accelerates. Your roof might start bowing, increasing the risk of collapse (but this could take years of damage and neglect). Left untouched, your roof will need an early replacement and your roofer will need to replace more of the roof deck in the process.

How to Prevent Ice Dams

It’s a lot easier to prevent ice dams than to deal with the damage they cause. The best way to protect against ice dams is via a four-pronged approach.

1. Insulation

A well-insulated attic goes a long way towards preventing ice dams. Attic insulation prevents heat from escaping from the living space into the attic. If the peak stays cold, the snow won’t melt and trickle down the roof.

The code minimum for attic insulation in Minnesota is R-49, but insulating your attic to R-60 is even better. If your attic is under-insulated, consider adding another layer. Or, if your insulation is old and damaged, you may need to replace it entirely.

2. Ventilation

Attics also need to be ventilated so heat can escape. If your attic is well-ventilated, it will be the same temperature as outside – which is what you want.

To tell whether your attic is adequately ventilated, just go up there. If the space feels overly warm and stuffy, you could probably use more vents. Talk to your roofer about adding some soffit vents or a ridge vent. This will also help your home’s energy efficiency!

3. Roof Underlayment

The underlayment is typically installed over the roof deck under the shingles. When you live in a snowy area, your roof should also have a good-quality ice and water barrier in addition to the underlayment.

An ice and water barrier won’t necessarily prevent ice dams from forming. However, it will limit water damage if ice dams do form. Imagine an ice dam forms on the edge of your roof and a little water seeps past your shingles. The ice and water barrier beneath the shingles will prevent the water from penetrating the roof deck. You may still need to have some shingles replaced if they’re damaged by the ice dam, but your roof deck should be okay.

4. Snow Shoveling

The final line of defense against ice dams is shoveling the snow off your roof. This is a great temporary solution if you need more insulation or ventilation but need to wait. If you shovel the snow away before it has a chance to melt, you won’t get ice dams. Even if your roof is well vented and well insulated, shoveling after a heavy snowfall is a good idea.

You can purchase long-handled roof shovels at most home improvement stores. These enable you to pull snow off the roof from the ground. For best results, start shoveling before the snow has a chance to get too heavy or thick. Please remember to not go on the roof to shovel snow off – leave that to professional snow removers.If you understand how they form and take a four-pronged preventative approach, you should be able to keep ice dams to a minimum. Contact Midwest Roofing Siding & Windows if you need help preparing your roof for winter to prevent ice dams from forming on your Twin Cities home. We can assess your insulation and ventilation needs, repair roof damage, and more.

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