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What Causes Ice Dams & How To Prevent Them

February 11, 2022
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An ice dam will form at the bottom of your roof, which can allow water to penetrate your roof.  

When the snow melts on a roof, it will run down until it meets the unheated bottom edge of the roof, where it freezes.

This forms the ice dam, causing the water to back up beneath the shingles, or underneath the siding.

Because of the heavy snow in our area, we've seen an influx of calls with many people worried about a roof leak, likely caused by an ice dam.

Many homeowners fear the worst when they begin to see water stains or an active leak.  It's understandable. No one wants to see water coming into their home causing damage.

This often causes many people to think that their roof is in shambles, but this is not always the case.

The best way to remove ice dams is to set up a prevention plan that won't allow them to form in the first place.

In the article below, our roofing specialists will go over a few helpful details on how to prevent ice dams.

What Causes Ice Dams?

An ice dam forms when the snow on the upper, warmer part of your roof melts and flows down to a colder eave overhang and freezes.

As the ice accumulates, it blocks additional snowmelt from flowing off the roof.

This causes the ice and snow to back up under the roof shingles, where it melts again and soaks the roof sheathing and leaking into the attic.

From there, it can soak the attic insulation, making it much less effective.

After that, it can leak through the drywall in your ceiling, down into a light fixture, and into your living space, causing water damage.

Large ice dams can be very heavy and damage gutters, and present a safety hazard to anyone below. 

Ice dams can only be formed when the space inside an attic along the underside of the roof deck is above freezing.

Ice dams usually start or worsen after a heavy snow because of snow's insulating properties.

The snow traps warm air beneath the snow causing it to melt. 

Preventing an ice dam requires the air in the attic or against the bottom of the roof to remain cold.

If it does, it can never melt the snow lying on top of the roof, eliminating the water necessary for ice dams.

Some of the best ways to prevent an ice dam from occurring are replacing old insulation with better insulation (not more insulation, just better insulation than what you currently have), sealing air leaks, and better ventilation.

Roof ventilation under the roof deck keeps colder outside air circulating through the attic, preventing it from warming above the freezing point.

Proper insulation in the ceiling below the attic prevents warm air from rising into the attic space to melt snow on your roof.

Ice dams can cause significant damage

Should I Call A Roofing Contractor About Ice Dams?

Discussing your ice dams with a professional roofing company is never a bad idea. However, roofers are unable to help stop a roof leak if it is caused by an ice dam.  

A roof leak due to an ice dam is more about the structure of your home and what is going on inside than it is about the state of your roof.

The formation of ice dams and the corresponding leaks they cause can make it seem like you need a roofer to come out to your house immediately, but they will not be able to stop the leak.  

One of the reasons they won't be able to help is because ice dam protection starts on the inside of the home.  Doing things such as having proper ventilation systems set up, decreasing house humidity, sealing air leaks, and replacing insufficient insulation can help prevent ice dams from forming.

Another reason a local roofing company can't help you is that it's unsafe to be on a roof during the winter. Due to roof ice, we don't advise homeowners to get on the roof, even to use things like snow rakes, or roof rakes, as it can lead to injury or cause damage to shingles. 

When the area gets several feet of snow, like we've seen this winter, it's not a good idea for anyone to get on the roof. 

The best way to make sure that your home stays free from the types of damage an ice dam buildup can cause is to prevent them from happening in the first place. 


How To Prevent Ice Dams

Better or Newer Insulation

A properly insulated attic minimizes heat escape through the ceiling. To be clear, this doesn't mean additional insulation or more insulation, and this means better insulation.

This virtually eliminates the possibility of snow melting and refreezing at the base of the roof.

The amount and type of insulation you need will vary depending on your location, the style of your home, and other factors like your lifestyle.

If you have an open attic, you should insulate the attic floor as well.

If you have a finished second-story with a finished ceiling that is directly against the roof, you should insulate the rafter spaces in combination with ventilation baffles.

This will eliminate any heat source from reaching your entire roof deck and heating it to a point where it can melt snow on the roof. 

Sealing air channels from the living space below the attic is just as important as fixing poor insulation.

Gaps around plumbing pipes or chimneys can be a significant source of heat flow into the attic.

Sealing these gaps should be part of your overall insulation strategy. 

The benefit of a comprehensive insulation effort is that it helps prevent ice dams from forming on a snow-covered roof and reduces energy costs.

However, insulation alone rarely is enough to prevent ice dams.

It should be done in conjunction with improved ventilation. 

Sealing Air Leaks

Sealing air leaks can help prevent ice damming on your roof. Frost will get into your attic from air leaks and can cause damage to walls and soggy insulation.

Another condition to check is to make sure that any kind of exhaust fan is never exhausted into the attic and that it is exhausted directly to the exterior.

This means that even if the exhaust fan is pointed at a roof vent, that's not enough. Having it just pointed at a roof vent allows moist air to get back into the attic.

The number one way to prevent frost accumulation in an attic is to seal off attic air leaks.

Even if you notice a small air leak, these can add up to a lot of frost accumulation in the attic. Make sure that you are sealing all attic leaks.  It’s important to seal all attic air leaks, not just the big ones. If you don't seal these, you're going to have a harder time preventing ice dams.

Once you have the leaks sealed, you want to check the roof and soffit vents are properly vented. 


Roof and Soffit Vents

If your home has proper insulation, you probably won't have to worry about ice dams.

By circulating cool outside air in the attic space, the roof temperature remains below freezing, so it can't melt the snow on the roof.

A cold attic means you won't have to worry about ice dams, and a warm attic almost always leads to destructive dams.

The minimum ventilation area should be about one sq. ft. of vent per 300 square feet of ceiling area when half the vent area is low on the roof and half is high.

Figuring all of this out can be a bit complex.

You'll have to examine your existing vents to find the area of each, which is stamped on them.

A general rule of thumb is to put an 8-in. x 16-in. vent in the underside of the soffit in every other rafter space.

If you need to rebuild the soffit ventilation, install a continuous 2-1/2-in.-wide "strip" vent because it will look better.

You should also install a continuous ridge vent along the peak.

If the ridge on your roof is much shorter than the roof edge, add the standard square-shaped roof vents near the peak.

Make sure you add enough, so their ventilating area is almost equal to the size of soffit vents.


You should waterproof your underlayment

Waterproofing Underlayment

If you are building a new home or installing a new roof on your current home, ensure that waterproofing shingle underlayment is installed before your roof shingles are applied.

This underlayment is entirely resistant to water and is a critical last line of defense against leaks, preventing excess water from getting into your home.  

Shingle underlayment does not prevent ice dams, but it will prevent backed-up water from entering the house, leading to wet insulation and water stains.

Keep Gutters Clean

If your gutters are clogged or backed up, this can prevent the removal of water as the snow and ice begin to melt.  If there isn't a way for the water to be removed from the roof, it'll find other places to drain to, like siding. 

Keeping your gutters clean will help prevent this.

Trust Your Roof To The Roof Repair Experts 

Many roof types get ice dams during the winter, so you're not alone.

However, you can prevent them from forming on your roof with proper insulation and attic ventilation, and you won't have to break out your ice picks or snow rakes.

The best time to prevent ice dams is before the outdoor temperature drops. If you're dealing with ice dams, our roofers can help set up a prevention plan once the weather breaks. 

If this winter has made you worry that your roof is falling apart or that you have multiple leaks and are going to need to replace your entire roof, you can breathe a sigh of relief.  With the amount of snow our area has received this year, ice dams have had homeowners on edge. 

Our roof repair contractors can help you make sure your roof will hold to ice dams with a prevention plan, and we can repair or replace the problem areas and help make sure that your home and your family are protected from all that Ohio's snowy winters throw at you. 

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